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Article

Gibberellins Target Shoot-Root Growth, Morpho-Physiological and Molecular Pathways to Induce Cadmium Tolerance in Vigna radiata L.

by
Haroon Rashid Hakla
1,
Shubham Sharma
1,
Mohammad Urfan
1,
Narendra Singh Yadav
2,
Prakriti Rajput
1,
Dinesh Kotwal
1,
Arafat Abdel Hamed Abdel Latef
3,* and
Sikander Pal
1,*
1
Plant Physiology Laboratory, Department of Botany, University of Jammu, Jammu 180006, India
2
Department of Biological Sciences, University of Lethbridge, Lethbridge, AB 403587, Canada
3
Department of Biology, Turabah University College, Turabah Branch, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia
*
Authors to whom correspondence should be addressed.
Agronomy 2021, 11(5), 896; https://doi.org/10.3390/agronomy11050896
Submission received: 3 April 2021 / Revised: 28 April 2021 / Accepted: 29 April 2021 / Published: 2 May 2021
(This article belongs to the Special Issue Hormone Signaling Underlying Defense Responses and environmental Stresses in Crop Plants)
Browse Figures
Versions Notes

Abstract

:
Cadmium (Cd) inhibits plant growth, perturbs nutrient uptake, and affects chloroplast ultrastructure. The role of Cd stress in affecting growth and physiology and ameliorative effects of gibberellins (GAs) in Cd-induced toxicity in mung bean are lesser-known. This study comprehensively investigated Cd stress (CdCl2, IC50—500 µM L−1) with or without GA3 on mung bean (Vigna radiata L. Var. SML-668). In our methodology, a total of 80 mung bean plants (15 days old of uniform height) were divided into four groups, and each group (n = 20) was subjected to four different treatments (Control, CdCl2, GA3, CdCl2+GA3) twice during the entire life cycle of mung bean plants (until harvest 85–90 days). Results revealed negative impacts of Cd stress on shoot morphometry (plant height, leaf surface area, stem diameter, shoot fresh weight, number of leaves, number of pods, length, and diameter of pods), root morphometry (root length, root surface area, root dry weight, nodule number and nodule diameter), photosynthetic pigments, and agronomic traits. GA3 application ameliorated Cd stress by modulating shoot and root growth, improving overall plant metabolism, photosynthetic pigments, and shoot and root morphometry and transcript abundance of VrPCS1, VrIRT1, VrIRT2 and VrCD29. Thus, we propose GA3 application for the effective management of Cd-induced phytotoxicity in mung bean plants.

1. Introduction

Heavy metal (HM) contamination of the biosphere has increased sharply for the last few years and poses major concerns for the environment and human health worldwide. Metals, such as cadmium (Cd), copper (Cu), lead (Pb), and chromium (Cr), could appear in natural and agricultural areas and water bodies. Latest modeling approaches showed mean bioaccumulation factors of heavy metals follow the order Cd > Zn > As > Cu > Ni > Hg > Cr > Pb in large number of crops [1]. Among HMs, Cd pollution poses a serious threat to soil quality and human health upon consuming Cd polluted edible crops [2,3]. Hazardously, Cd toxicity is much higher than other organic toxic compounds, due to its greater mobility [4,5]. Cd is hardly degraded in soil, leading to biomagnifications in soil and plants growing in Cd polluted soils. In general, Cd is not a necessary element for plant growth and its excess has a series of harmful effects, including inhibition of plant growth, perturbed nutrient uptake, and chloroplast ultrastructure [4,5,6,7].Cd generates oxidative stress in plants via inducing the production of reactive oxygen species (ROS), such as superoxide anion radicals (O2−), hydroxyl radicals, and hydrogen peroxide (H2O2) [8,9].
Vigna radiata L. (mung bean) is a widely grown pulse crop in Asia. It is an economical source of protein for direct human consumption [1]. Mung bean is affected by drought [10,11], salinity [12], and other abiotic [13] and biotic stresses [14]. Mung bean plants suffer significantly from HM pollution also in the agricultural soils polluted from effluents of adjoining industrial areas [4,5,6,7]. Reduction in plant growth and pod size occurs under HM stress in mung bean [15,16,17]. Several biotechnological strategies have been adopted towards improving the HM stress management in crop plants [18], such as HM tolerance assisted by microbes [19], transgenics [20,21], and use of phytohormones [22,23]. A strong criticism for transgenic approaches of improving yield and abiotic or biotic stress tolerances of crop plants have impeded the acceptance of transgenic crops by the population world over [24,25]. Eco-friendly approaches (phytohormonal and microbe assisted) of improving HM stress tolerances in crops offers an alternate way without fiddling the genetic make of crop plants and germplasm erosion [26,27]. Literature survey showed scant information about the holistic impact of Cd stress on morphometrical, reproductive, physiological, and agronomical attributes on mung bean plants. Gibberellins (GAs) are important plant hormones implicated in several developmental and physiological processes in plants. GAs role in heavy metal stress management in plants is widely accepted. However, GAs role in reducing Cd-associated stress in mung bean plants is least explored and mostly confined to photosynthesis [28] and seedlings stages [29]. Thus, this study comprehensively investigated the effects of Cd stress on the mung bean plants and the role of gibberellic acid (GA3− a type of gibberellins) in mitigating Cd-induced stress markers. Keeping the current understanding of Cd stress in mung bean plants, this study was carried out to observe the impact of Cd stress on growth, as well as biochemical parameters of plants of V. radiata from seedling to fruiting stage in the presence of 500 µM/L GA3 concentration and to provide a theoretical basis for the risk assessment of heavy metal pollution and the maintenance of sustainable agricultural production.

2. Materials and Methods

  • Experiment 1: Growth of Young Plants in Hydroponics
Certified seeds of Vigna radiata L. (var. SML-668) were procured from the Agriculture station, Jammu, India. To determine the impact of Cd stress on establishing root and shoot system in young plants, uniform seedlings raised for five days by paper roll method on plain water (control), were subjected to four different treatment regimes viz. Control, CdCl2, GA3 and CdCl2+GA3 for 10 days. Young plants were harvested separately into shoot, root, and emerging leaves to measure root and shoot length, and number of emerging leaves and cotyledonary leaves.
  • Experiment 2: Growth of Plants in Soil
Experiments were conducted in the poly house (32.72° N 74.85° E) of the Department of Botany, University of Jammu, India. Certified seeds of Vigna radiata L. (var. SML-668) were sown in the field beds, at a uniform distance during September 2018 and 2019. At 10 days after sowing (DAS), uniform healthy seedlings were selected and transplanted to pots (26 cm height and 25 cm diameter) filled with 5 kg garden soil mixed with farmyard manure in the ratio of 3:1. A total of 80 mung bean plants (15 days old of uniform height) were divided into four groups, with each group (n = 20) subjected to four different treatments (Control, CdCl2, GA3, CdCl2+GA3), for the next 45 days with and without treatment of GA3 (500 µM/L) by soil drench method. Water was applied through surface irrigation at the three days interval based on the calculated evapotranspiration demand following the FAO-Penman Monteith model as described elsewhere [30]. Plants were then thoroughly investigated for changes in morphometrical, physiological parameters, and molecular pathways. Prior to CdCl2 application, IC50 was calculated for mung bean seedlings grown in Petri dishes over five days.

2.1. Shoot and Root Morphometry and Biomass

The number of cotyledonary and emerging leaves, seedling shoot length (SSL), seedling shoot biomass (SSB), seedling root biomass (SRB), and total root length (TRL), lateral root number (LRN), and TRL/R was measured for young plants grown in hydroponics system using paper roll method. Young root images were analyzed by freely available Image J software Version 1.52v.
For mature plants grown in soil, shoot height (cm), stem thickness (cm), leaf number (N), and leaf surface area (cm2) were measured on a weekly basis. Fresh and dry weights of leaves, stem, and roots were measured at the time of harvest [31]. Root length, root surface area, nodule number, and nodule diameter was measured at the harvesting stage. Root growth was imaged using a high-resolution camera (Nikon B500 Camera, New Delhi, India).

2.2. Histological Localization and Estimation of Cd Accumulation by Atomic Absorption Spectrometry

Histological localization of Cd2+ ions was performed with 0.5 M oxalic acid and visualized as white crystalline precipitates. Thin transverse sections of the stem were dipped for 10 min in a solution of 0.5 M Oxalic acid at room temperature. The sections were imaged using a high-resolution camera (Nikon B500 Camera, New Delhi, India). For the measurement of Cd content in mature plants, atomic absorption spectrometry (AAS, Shimazdu, Tokyo, Japan) was used [32].

2.3. Biochemical Estimations and Stress Indices

About 500 mg of fresh leaves were homogenized with ethanol (95%) (5 mL) to make a slurry, samples were centrifuged at 13,000 rpm for 10 min, and estimation of Chla, Chlb, and carotenoids (CAR) [33], sucrose content (a major photosynthate) [34] were carried. Protein estimation, ascorbic acid (ASA), and total phenols (TP) were performed as described [35]. Nodule leg hemoglobin content and Urease enzyme (EC 3.5.1.5) activity was measured by the Berthelot method [36] in the root nodules. Estimation of stress indices such as proline (PL) and malondialdehyde (MDA) was performed as described in Choudhary et al. [37].

2.4. Agronomic Traits

Economically important traits of mung bean plants such as pod diameter, pod length, pod fresh weight, pod dry weight, seed number/ten pods, 100 seeds weight, seeds weight/pod, seed SA, seed diameter, seed protein, and seed sugar content were measured at the harvesting stage using appropriate standard procedures as described elsewhere [38]. Seed attributes particularly, width, length, thickness, surface area, Ew, Ev, geometric mean (Dg), seed shape (Φ%), volume of the grain (V), percent seed germination (%G), and seed protein content (SPr) and seed total phenol content (STPC), were measured.

2.5. Quantitative PCR Analysis

Total RNA was extracted from frozen root samples using TriZol (Thermofisher, Waltham, MA, USA) with DNase treatment according to the manufacturer’s instruction. One microgram of RNA was reverse transcribed using cDNA Synthesis Kit (Thermofisher, Waltham, MA, USA) with oligodT as primers. Quantitative polymerase chain reaction (qPCR) analysis was conducted on QuantStudio™ 3 Real-Time PCR System (Applied Biosystems, Foster City, CA, USA), and the amplification curve was checked with software provided. The reaction included a SYBR green PCR master mix (Thermofisher, Waltham, MA, USA) with 4-folds diluted cDNA in the total volume of 20μL [35]. A comparative delta Ct (2−ΔCt) method was used to quantify the relative expression of Vigna radiata phytochelatin synthase 1 (VrPCS1), VrIron transporter 1 (VrIRT1), VrIron transporter 2 (VrIRT2) and Vr cadmium response (VrCDR29) with actin as endogenous control. Primer sequences are provided in [39].

2.6. Pearson Correlation Analyses

A pair-wise correlation between Cd stress with or without GA3 on plant fitness and agronomic attributes was carried out. Pearson’s correlation coefficient (r) was calculated using IBM SPSS 20.0 for ten traits (shoot height, stem thickness, leaf number, leaf surface area, root length) of plant fitness and agronomic importance (seed number, seed weight, seed weight/pod and seed surface area). A linear correlation coefficient (r) was calculated to understand the interaction of two factors at a time at p < 0.05 and p < 0.01 with a number of biological replicates (n = 20) for the following combination of treatments CN versus Cd, Cd versus Cd+GA3 and CN versus Cd+GA3. The r values fall in the range of +1 to −1, with positive values indicating a positive linear relationship among two treatments and –ve value indicating the negative relationship among treatments.

2.7. Statistical Analysis

Experiments were arranged in a randomized factorial design (2018 and 2019). Data obtained were analyzed by ANOVA and all means were separated at the p < 0.05 level using the Duncan test. All calculations and data analyses were performed using the IBM SPSS 20.0 for Windows software package, and the values were expressed by means and standard error (SE).

3. Results

3.1. Growth of Young Shoot-Root System under Cd Stress and after GA3 Application

The establishment of the young root system, cotyledonary leaves, and emergence of young leaves were affected under Cd stress. The development of cotyledonary leaves is a prerequisite for establishing a healthy young plant. Cd stressed plants showed 13% and 74% reductions in establishment of cotyledonary leaves and the emergence of young leaves compared to control plants (Figure 1a). GA3 applied to Cd stressed plants showed improvement in establishment and emergence of cotyledonary leaves and young leaves by 15% and 17%, respectively, compared to Cd alone treated plants. GA3 alone showed no signficant reduction in the emergence of young leaves over control (Figure 1a). Seedling shoot length (SSL) reduced by 13% in Cd stressed plants over control. While GA3 could improve SSL by 20% in Cd stressed plants compared to only Cd-treated plants. About 17% increase in SSL was noted in GA3 alone treated plants compared to control (Figure 1b). Seedling shoot biomass (SSB) and seedling root biomass (SRB) were reduced by 15% and 29% in Cd stressed plants over control. GA3 improved SSB and SRB by 22% and 21%, respectively, in Cd stressed plants compared to only Cd-treated plants. No significant change in SSB and SRB occurred in GA3 alone treated plants over control plants (Figure 1c).
For root growth, Cd stressed plants showed significant impact on establishing the young root system, such that 41%, 26%, and 54% reductions in total root length (TRL), lateral roots number (LRN), and total root length/ roots (TL/R) were recorded in Cd stressed plants over control. GA3 in Cd stressed plants showed improvements in TRL and TL/R over Cd alone treated plants. GA3 alone brought reductions in TRL, LRN, and TL/R by 16%, 22%, and 17% compared to control plants (Figure 1d,e).

3.2. Shoot Morphometery under Cd Stress and after GA3 Application in Pot Experiments

A consistent decrease in stem height and stem diameter was noted in Cd-treated plants (Figure 2a,b), with maximum reductions at 80 DAS. GA3 steadily improved stem height and stem diameter in Cd-treated plants, with a maximum increase recorded at 70 DAS over Cd-treated plants (Figure 2a,b). GA3 alone improved stem height significantly at 50–80 DAS and while stem diameter in a non significant manner over control plants. A constant decrease in leaf number was noted in Cd-treated plants; with a maximum reduction at 70 and 80 DAS compared to controls (Figure 2c). GA3 application to Cd-treated plants could ameliorate negative Cd impact on leaf number, with most significant increases at 70 and 80 DAS over Cd alone treated plants. No significant change in leaf number was recorded for.
GA3 alone except at 80 DAS (Figure 2c). At all observation points, leaf surface area (LSA) was reduced in Cd-treated plants, with maximum reduction recorded at 60, 70 and 80 DAS over control plants. GA3 improved LSA in Cd-treated plants non significantly at over Cd-treated plants at all observation points (Figure 2d). Similarly, increased LSA was recorded in GA3 alone treated plants over control plants (Figure 2d).

3.3. Effect of GA3 on Root Surface Area and Root Nodules Attributes under Cd Stress in Pot Experiments

Root length (RL) and root surface area (RSA) play an important role in the absorption of water and uptake of minerals from the soil solution. In the current study, Cd stressed plants showed significant reductions in RL and RSA over control plants. Furthermore, GA3 applied to Cd stressed plants increased RSA significantly over Cd stressed plants (Figure 2e,f). No significant change in RSA under GA3 alone was observed compared to control plants (Figure 2e,f).
Root nodule number (RNN) in Cd stressed plants decreased at all the observation points (30, 45, 60, and 75 DAS) over control. GA3 improved RNN in Cd-treated plants at 30, 45 and 75 DAS, while declined it at 60 DAS compared to Cd stressed plants (Figure 2g). GA3 alone enhanced RNN at 30 DAS, while reduced RNN at 45, 60 and 75 DAS over control (Figure 2g). Root nodule diameter (RND) showed a consistent decline in Cd stressed plants, with a maximum reduction (43%) noted at 75 DAS over control (Figure 2h). GA3 improved RND in Cd stressed plants significantly at 30, 45 and 75 DAS over Cd stressed plants. RND also improved in GA3 alone treated plants, with a increase observed at 45, 60 and 75 DAS over control plants (Figure 2h).
Urease activity in root nodules decreased under Cd stress at 30, 45, and 60 DAS, while a nonsignificant increase in activity at 75 DAS occurred compared to control. GA3 could improve urease activity consistently in Cd stressed plants over Cd-treated plants (Table 1). GA3 alone could improve urease activity at 45 and 60 DAS compared to control. A consistent reduction in legHb content was recorded in nodules of Cd stressed plants at all observation points (30, 60, and 75 DAS), with a maximum decline 57% noted at 60 DAS over control. GA3 could improve legHb contents in Cd-treated plants at all the observation points, with a maximum increase of 253% recorded for 60 DAS over Cd stressed plants (Table 1). Furthermore, GA3 alone reduced legHb content at 30 and 40 DAS, while increased it at 60 and 75 DAS compared to control (Table 1).

3.4. Effect of GA3 on Plant Biomass under Cd Stress

Plant biomass is a good indicator of plant fitness under abiotic stress. In the present study, Cd stressed plants showed 49% reduction in fresh leaf biomass (FLB) and 29% in dry leaf biomass (DLB) compared to control (Figure 3a,b). GA3 could improve FLB and DLB by 24% and 63% in Cd stressed plants over Cd-treated plants alone (Figure 3a,b). GA3 alone improved FLB and DLB compared to control plants. Stem fresh (SFB) and stem dry biomass (SDB) showed a reduction by 12% and 11% in Cd stressed plants over control. GA3 supplementation to Cd stressed plants witnessed increased SFB (8%) and SDB (9%) compared to Cd alone treated plants (Figure 3c,d). GA3 alone could improve SFB (11%) and SDB (12%) over untreated control plants. Root biomass is a key determinant for the successful survival of a plant under abiotic stresses (Figure 3e,f). Under Cd stress, 14% and 50% reduction in root fresh biomass (RFB) and root dry biomass (RDB) was noted over control. GA3 could improve both RFB and RDB by 6% and 35% in Cd stressed plants over Cd-treated plants. GA3 alone reduced RFB and RDB over control plants (Figure 3e,f).

3.5. Effect of GA3 on Photosynthetic Pigments and Soluble Sugar under Cd Stress

Photosynthetic pigments suffered damage under Cd stress such that a consistent decrease in Chla content at all the observation points (30, 45, 60, and 75 DAS), with maximum reduction (55%) occurred at 30 DAS compared to control (Table 1). GA3 could improve Chla content consistently, with a maximum increase (75%) recorded at 30 DAS over Cd alone treated plants. GA3 alone improved Chla content at all observation points, with maximum enhancement (20%) noted at 75 DAS compared to control plants (Table 1). Contrary to Chla, under Cd stress, Chlb content showed a consistent increase at all observation points, with a maximum increase 225% recorded at 60 DAS compared to control plants. Furthermore, GA3 could increase Chlb content throughout the experiment, with maximum improvement (52%) noted at 30 DAS over Cd alone treated plants (Table 1). GA3 alone could improve Chlb content at all the observation points, with a maximum increase (157%) being recorded at 30 DAS compared to control plants. For carotenoids (CARs), under Cd stress, content showed an upward trend, with a maximum increase (59%) noted at 30 DAS over control plants. GA3 improved CAR content maximally (66%) at 75 DAS compared to only Cd-treated plants. GA3 alone could improve CAR content at all the observation points, with a maximum increase (232%) recorded at 30 DAS compared to control plants (Table 1). Total soluble sugars (TSS) amount was significantly reduced at 30, 45, 60, and 75 DAS in Cd stressed plants compared to control. GA3 supplied to Cd stressed plants significantly enhanced TSS by 81% and 100% at 60 and 75 DAS than Cd alone treated plants. GA3 alone could improve TSS significantly at 75 DAS over control plants (Table 1).

3.6. Effect of GA3 on Stress Indices and Antioxidant System in Pot Experiments

Stress indices such as malondialedhye (MDA, membrane damage indicator) and proline (PL) play a significant role in evaluating the physiological status of a plant under abiotic stress. In the present study, Cd stress was shown to increase MDA content at all the observation points, with the most significant membrane damage (87%) recorded at 60 DAS compared to control plants (Table 1). GA3 could bring a decline in MDA content in Cd stressed plants maximally at 75 DAS over Cd-treated plants. GA3 alone significantly increased MDA (34%) at 45 DAS compared to control plants. Under Cd stress, PL content increased sharply, with a maximum increase (270%) at 60 DAS compared to control plants. GA3 supplementation to Cd stressed plants further improved PL content at all the observation points, with a maximum increase (86%) recorded at 45 DAS over Cd alone treated plants. A consistent increase in PL occurred under GA3 alone, with a maximum increase (170%) noted at 60 DAS over control plants (Table 1).
Among antioxidants, total phenol content (TPC) increased maximally (25%) at 60 DAS in Cd stressed plants compared to control plants (Table 1). GA3 applied to Cd stressed plants showed a decline in TPC content at all the observation points, with maximum reduction (24%) noted at 75 DAS over Cd alone treated plants. In comparison, GA3 alone treated plants showed a maximum increase in TPC (30%) at 30 DAS (Table 1).

3.7. Effect of GA3 on Accumulation, Translocation, and Localization of Cd Ions

Compared to control plants, Cd stressed plants showed 61%, 126%, and 88% higher accumulation of Cd in leaf, shoot, and root tissue (Figure 4a). GA3 application to Cd stressed plants reduced accumulation of Cd by 35%, 34%, and 46% in leaf, shoot, and root tissues compared to Cd alone treated plants (Figure 4a). Bioaccumulation factor (BAF) from soil to root transfer of Cd showed a marked increase by 14.5 fold-over soil concentration of Cd alone (Figure 4b). GA3 application to Cd stressed plants showed a significant reduction of BAF of roots from the soil by 7.8-fold compared to BAF in Cd alone (by 14.5-fold) (Figure 4b). Translocation factor (TF) from shoot-leaf showed no major change in Cd alone, and Cd stressed plants supplemented with GA3 (Figure 4c). About 75% and 65% accumulation of Cd has been noted in pods and seeds of Cd stressed plants compared to control plants grown in soil in pots. GA3 application reduced Cd accumulation by 67% and 89% in pods and seeds compared to Cd alone treated plants. Compared to Cd stressed plants, significant reductions in Cd ions accumulation were recorded in pods and seeds applied with GA3 plus Cd (Figure 4d). For histological localization of Cd2+ ions, white crystalline precipitates of Cd oxalate were observed in the transverse sections (T.S.) of the stem of plants under Cd stress. Localization was more pronounced in the cortex areas of Cd stressed plants, while Cd oxalate crystals were few in GA3 applied Cd plants (Figure 4e–h).

3.8. Effect of GA3 on Genes Regulating Cd Uptake and Transport

Expression of genes inducing Cd2+ ions sequestration was enhanced under Cd stress compared to the control. Such that 1.7, 2.5, 1.6-fold increase in expression of VrPCS1, VrIRT1, and VrIRT2 was noted in Cd stressed seedlings compared to control. GA3 application further elevated expressions of VrPCS1, VrIRT1 and VrIRT2 over Cd treatment (Figure 5a–c). GA3 alone could not modulate expressions of these genes significantly compared to control. Increase in uptake of Cd ions under Cd stressed plants over control was linked with elevated expression of VrIRT1 and VrIRT2 over control plants. GA3 application lowered Cd accumulation in young plants; this reduction in Cd ions accumulation could be attributed to a decline in expression of VrIRT1 and VrIRT2 compared to only Cd-treated seedlings (Figure 5b,c). GA3 alone also improved VrIRT1 expression over control though insignificantly compared to control. Elevated expression, 2.2-fold of VrCDR29 noted in Cd stress alone compared to control. GA3 application to Cd stress further improved VrCDR29 expression by 1.7-fold compared to only Cd treatment (Figure 5d).

3.9. GA3 Improves Agronomic Traits Affected by Cd Stress

A visible reduction in pod length and seed size was observed under Cd stress, while GA3 application could mitigate negative impacts of Cd stress on pod length and seed size (Figure 6). For pod length, Cd-treated plants showed 21% reduction, while GA3 improved pod length by 11% in Cd stressed plants over Cd alone (Figure 7a). Cd-treated plants showed an 8% reduction in pod diameter compared to control plants. GA3 could improve pod diameter by 17% in Cd stressed plants (Figure 7b). GA3 applied alone increased pod diameter by 58% over control plants (Figure 7b). Approximately 34% reduction in pod number/plant was recorded in Cd stressed plants over control plants.
About 25% increase in pod number/plant was recorded for GA3 applied Cd stressed plants over Cd alone treated plants. No significant change in pod number/plant was recorded for alone GA3 treated plants over control plants (Figure 7c). About 49% and 52% reduction in pod fresh and pod dry weight was noted in Cd stressed plants compared to control plants. GA3 in Cd stressed plants showed significant improvement in pod fresh (57%) and pod dry weight (107%) over Cd alone treated plants (Figure 7d,e). Interestingly, a 108% and 237% increase in pod fresh and pod dry weight was recorded for alone GA3 treated plants compared to control plants (Figure 7d,e).
For seed, Cd stress was able to influence several important seed attributes viz. seed number/ten pods for normal and aborted seeds, 100 seeds weight, seeds weight/pod, seed width (W), seed length (L), seed thickness (T), seed surface area (SA), mean geometric diameter (Dg), sphericity (Φ%), seed volume (V) and seed germination percentage (%G). Such that 19%, 40%, and 47% reduction in seed number/ten pods, 100 seeds weight and seed weight/pod was recorded in Cd stressed plants over control plants. However, GA3 application in Cd stressed plants showed 32%, 35%, and 67% improvement in these seed attributes over alone Cd-treated plants (Figure 7f–h). GA3 alone improved seed number/ten pods by 9.5% and reduced 100 seeds weight and seed weight/pod by 20% and 10%, respectively, compared to control plants (Figure 7f–h). For seed geometric attributes, about 13%, 15%, 14%, and 16% reduction in W, L, T, and seed surface area (SA) was recorded in Cd stressed plants compared to control plants (Figure 7i, Table 2). GA3 application to Cd stressed plants improved W, L, T, and SA by 8.47%, 15.29%, 8.23%, and 13.27%, respectively, over Cd alone treated plants. Similarly, 13.77% and 35.89% reduction in Dg, and V was recorded in Cd stressed plants over control plants. GA3 application in Cd stressed plants showed 10.46% and 34.79% improvement in Dg, and V over Cd alone treated plants. Contrary, GA3 application alone reduced Dg by 8.31% and V by 22.91%compared to control plants alone. While no significant change in Φ%was recorded in Cd stressed plants, though an insignificant decrease of 4% was recorded for GA3 applied Cd stressed plants compared to alone Cd-treated plants (Table 2). Seed protein content under Cd stress declined 36% compared to control seeds. Application of GA3 in Cd stressed plants further declined seed protein content by 20% over Cd-treated plants. Interestingly, seed protein content declined by 35% in GA3 alone treated plants over control plants (Table 2). Seed sugar content decreased significantly in Cd stressed plants over control (Figure 7j). GA3 alone or with Cd stress improved seed sugar content significantly (Figure 7j). Seed TPC in Cd stressed plants showed a significant increase (241%) over control plants. GA3 applied Cd stressed plants showed a 92% reduction in seed TPC over TPC of seeds of Cd alone treated plants. About 43.46% reduction in seed TPC was noted in alone GA treated plants compared to control (Table 2).

3.10. Pearson Correlation Analysis

A significant linear correlation (r) for stem height, stem diameter, and leaf number were noted for Cd stress alone (Table 3). Pearson’s correlation coefficient (r) for shoot traits under Cd stress showed linear correlation; however, a significant positive correlation was noted for stem diameter (Table 3). A negative correlation was noted for root length under Cd stress (Table 3). GA3 applied to Cd stressed plants showed a positive correlation for stem diameter, leaf number, and root length, while a negative correlation noted for stem height and leaf surface area (Table 3). For agronomic traits, seed number, seed weight, seed weight/pod showed a positive correlation with Cd stress, while a negative correlation was found for seed surface area (Table 3). While all agronomic traits except seed number showed a negative correlation between GA3 applied Cd stressed plants and Cd alone treated plants (Table 3).

4. Discussion

Cadmium (Cd) is a nonessentialheavy metal known to affect human health and plant growth and metabolism [2,40]. Being highly active Cd, its excess in soil often accounts for perturbed metabolism and growth defects leading to reduced yield in crops of commercial importance [4]. The decrease in shoot and root lengths and fresh and dry biomass, due to heavy-metal stress has been reported in mungbean [8], Arachis hypogea [41], and sunflower [42]. The reduction in plant height under Cd stress can be supported with similar observations recorded in Vigna radiata (L.) Wilzeck cultivars PDM-139 and K-851 subjected to 0.2 mg/L of Cd exposure showed a significant reduction in plant height [43]. However, improved plant height recorded in Cd stressed plants upon application of GA3 compared to Cd stressed plants could be attributed to the positive impact of GA3 on inducing plant growth (Figure 1). Our observations are supported by similar findings, wherein application of GA (50 µM) to Brassica napus L. grown in Cd (0, 50, and 100 μM) hydroponics could increase plant height compared to only Cd hydroponics [44]. Similar to our observations of reduced leaf number and leaf SA in mung bean plants under Cd stress, reduction in leaf number and leaf SA have been reported in V. radiata (L.) Wilczekwas subjected to increased levels of Cd in the soil medium [45]. Improved leaf SA of Cd stressed plants applied with GA3 could be linked with the established impact of GAs on the leaf elongation rate (LER)viaactivating expression of genes of cell elongation, i.e., α-expansins, one β-expansin, and xyloglucanendotransglycosylase [46]. Reductions in both fresh and dry biomasses of Cd stressed plants could be attributed to Cd interference in the normal functioning of enzymes of the Calvin cycle, CO2 fixation, phosphorus, and carbohydrate metabolism leading to stunted plant growth and inhibition of photosynthesis [19,47].
Plants often respond to soil HM stress by reducing root length and root surface area, to minimize the root area exposition to HM pollution [48]. The decrease in root length, root surface area, and root biomass both in young plants (Experiment 1) and mature plants (Experiment 2). The role of Cd in decreasing nodulation and activity of nitrogen metabolizing enzymes has been established [49]. Higher concentrations of Cd have been observed to induce nodule senescence and decrease in legHb content in leguminous plants [49]. Contrary to earlier reports, Cd stress was observed to increase nodule number/plant over control plants; interestingly, this increase in nodule number/plant was found to be associated with a significant reduction in nodule diameter and nodule surface area. However, the application of GA3 was able to improve nodule diameter at all observation points with a maximum increase recorded at 75 DAS compared to only Cd stressed plants. Similar to observations reported earlier, Cd stress loweredthe nodule legHb content significantly over control plants; however, supplementation of GA3 to Cd stressed plants showed improvement in nodule legHb content. This reduction in legHb content under Cd stress could be attributed to the production of a higher number of reactive oxygen species with a detrimental impact on nodules [50].
A positive correlation existed between the accumulation of Cd in shoot tissue and its localization. Significantly accumulated Cd in Cd stressed plants followed shoot > root > leaf, while GA3 application could reduce Cd accumulation and root-shoot and shoot to leaf translocation significantly. Similarly, the accumulation of Cd was higher in pods than seeds, while GA3 application reduced this accumulation by a significant factor. This significant reduction in Cd accumulation in GA3 treated plant tissues and its translocations from root to shoot and shoot to leaf could be linked with elevated expressions of genes regulating Cd uptake (VgCDR), phytochelatin synthesis (VgPCS1 and VgPCS2), and VgIRT1 compared to Cd stressed plants.
Reductions in photosynthetic pigments (Chla, Chlb and CAR) in Cd stressed plants may be linked to the inhibitory impact of Cd-induced generation of ROS and lipid peroxidation and inhibiting Chl biosynthesis by competing with Mg ions, consequently leading to damage of PS II [51]. Application of GA3 ameliorated the negative impact of Cd on photosynthetic pigmentsviareducing the production of ROS and damage to the cell membrane by improving antioxidant activity of Cd stressed plants compared to Cd alone treated plants. Exogenous applications of GA3 have been shown to improve the contents of photosynthetic pigments by stabilizing and inhibiting the dissociation of the light-harvesting complex from PS II core, under Cu stress in Helianthus annuus L. [52].
Cd stressed plants showed an increase in membrane damage as indicated by enhanced levels of MDA throughout the plant’s life cycle after the imposition of Cd stress. Application of GA3 was observed to reduce membrane damage in Cd stressed plants, probably via reducing the production of ROS compared to Cd stressed plants (Table 1). Findings agree with Cd-induced membrane damage and higher production of superoxide radicals and membrane lipid peroxidation products recorded in seedlings of Vigna aconitifolia L. [53]. Enhanced levels of PL in Cd stressed plants could be linked with effective HM stress management; moreover, GA3 induced further increase in PL content in Cd stressed plants can be associated with reducing ROS production. GA3 induced increase in PL production and its implication in bud outbreak has been recorded in Prunus avium (sweet cherry) [54].
Phenolic acids play pivotal roles in abiotic stress management, particularly by neutralizing or scavenging ROS. TPC is a good indicator of total phenolics content in a plant system under abiotic stresses in plants. In the present work, enhanced TPC in Cd stressed plants could be linked with the plant’s inbuilt response towards enhanced ROS production and their management. While GA3 induced a small decrease in TPC of Cd stressed plants could be attributed to the reduction of ROS levels and returning of normal growth conditions compared to Cd stressed plants. Enhanced levels of total phenolics in GA-treated Vitis vinifera L. cv. Muscat has been recorded to play important roles in the development of grapevine tissues [55]. Soil HM pollution has been shown to affect the activity of nitrogen metabolism enzymes such as urease and nitrification dynamics in the soil-rhizosphere zone [56]. At low concentrations (0.5 mg/kg soil), Cd2+ cations were able to up-regulate the urease activity; though at higher concentration activity got declined considerably [56]. Similar observations were also recorded for Cd stressed plants and elevated activity of urease activity in GA3 applied plants.
Cd stress has been observed to reduce agronomic traits of V. radiata L. [15], such that plants subjected to 3, 6, 9, and 12 mg/kg soil Cd toxicity showed a reduction in the number of pod/plant, pod length, pod fresh weight, pod dry weight, number of seeds/pod and number of seeds/plant [15]. This investigation also witnessed a reduction in pod size, pod length, pod diameter, pod fresh and dry weights, seed number/pod and plant, seed weight under Cd stress (Figure 6 and Figure 7). Besides, reduced seed surface area, sugar content, protein content, and geometric attributes were also noted under Cd stress. GA3 supplementation was able to significantly mitigate the negative impact of Cd stress on all the prementioned agronomic attributes.
A Pearson correlation analysis also revealed the negative impact of Cd stress on agronomic and growth parameters of vigna plants. Moreover, GA3 application improvedthe negative impact of Cd stress on the growth and agronomic traits considerably. Due to these findings, we propose the application of GA3 for significantly reducing the Cd stress-associated damages in mung plants.

5. Conclusions

Thisstudy demonstrated the negative impact of Cd toxicity on mung bean plants at the morphological, physiological, and agronomical level. GA3 application was observed to reduce Cd-induced stress through several morphological and physiological adaptations without compromising economic attributes. Wepropose GA3 application for the management of Cd-induced stress in mung bean plants.

Author Contributions

Conceptualization: S.P., N.S.Y. and A.A.H.A.L.; methodology; H.R.H., M.U., S.S., P.R. and D.K.; software: S.P.; validation: S.P., H.R.H., M.U., S.S., P.R. and D.K.; formal analysis: H.R.H., M.U., S.S. and D.K.; investigation: H.R.H., M.U., S.S. and D.K.; writing—original draft preparation: S.P., N.S.Y. and A.A.H.A.L.; writing—review and editing: S.P., N.S.Y. and A.A.H.A.L.; visualization: S.P.; supervision: S.P. and A.A.H.A.L.; project administration: S.P.; funding acquisition: S.P. and A.A.H.A.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by UGC-SAP-DRS, and Taif University Researchers Supporting Project number (TURSP-2020/72), Taif University, Taif, Saudi Arabia.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

Authors would like to thank Department of Botany, University of Jammu for extending laboratory facilities and technical support. The research work was supported by CSIR-Junior Research Fellowship, Government of India to Urfan Mohammad.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Effect of GA3 on the growth of young mung bean plants under cadmium (Cd) stress in hydroponics.Effect of GA3 with or without cadmium (Cd) stress on the number of cotyledonary and young emerging leaves (a), seedling shoot length (b), seedling shoot biomass (SSB) and seedling root biomass (SRB) (c), length of the root system (d), total root length (TRL), lateral root number (LRN), and total lateral roots (TLR)/R (e) in paper roll method grown under control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions hydroponically. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Figure 1. Effect of GA3 on the growth of young mung bean plants under cadmium (Cd) stress in hydroponics.Effect of GA3 with or without cadmium (Cd) stress on the number of cotyledonary and young emerging leaves (a), seedling shoot length (b), seedling shoot biomass (SSB) and seedling root biomass (SRB) (c), length of the root system (d), total root length (TRL), lateral root number (LRN), and total lateral roots (TLR)/R (e) in paper roll method grown under control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions hydroponically. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
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Figure 2. Effect of GA3 on the growth parameters of mung bean plants under cadmium (Cd) stress in soil. Effect of GA3 with or without cadmium (Cd) stress on stem height (cm) (a), stem diameter (cm) (b), leaf number (N) (c), leaf surface area (cm2) (d), root length (cm) (e), root surface area (cm2) (f), nodule number (g), nodule diameter (cm) (h) of mung bean plants grown in soil in pots at 20 days after sowing (DAS), 30 DAS, 40 DAS, 50 DAS, 60 DAS, 70 DAS, and 80 DAS for (a–d) and 30 DAS, 45 DAS, 60 DAS, and 75 DAS for (e–h) grown under control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Figure 2. Effect of GA3 on the growth parameters of mung bean plants under cadmium (Cd) stress in soil. Effect of GA3 with or without cadmium (Cd) stress on stem height (cm) (a), stem diameter (cm) (b), leaf number (N) (c), leaf surface area (cm2) (d), root length (cm) (e), root surface area (cm2) (f), nodule number (g), nodule diameter (cm) (h) of mung bean plants grown in soil in pots at 20 days after sowing (DAS), 30 DAS, 40 DAS, 50 DAS, 60 DAS, 70 DAS, and 80 DAS for (a–d) and 30 DAS, 45 DAS, 60 DAS, and 75 DAS for (e–h) grown under control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
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Figure 3. Effect of GA3 on the biomass of mung bean plants under cadmium (Cd) stress in soil.Effect of GA3 with or without cadmium (Cd) stress on fresh leaf biomass (a), dry leaf biomass (b), stem fresh biomass (c), stem dry biomass (d), root fresh biomass (e) and root dry biomass (f) of mung bean plants grown in soil in pots at time of harvest. Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Figure 3. Effect of GA3 on the biomass of mung bean plants under cadmium (Cd) stress in soil.Effect of GA3 with or without cadmium (Cd) stress on fresh leaf biomass (a), dry leaf biomass (b), stem fresh biomass (c), stem dry biomass (d), root fresh biomass (e) and root dry biomass (f) of mung bean plants grown in soil in pots at time of harvest. Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
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Figure 4. Effect of GA3 on accumulation, translocation, and localization of cadmium (Cd) in mung bean plants. Effect of GA3 on cadmium (Cd) accumulation (ppm/g dry weight) in leaf, shoot, and root tissue (a), bioaccumulation factor (BAF, Cd accumulation root/soil) (b), translocation factor (shoot/root and leaf/shoot) (c), Cd accumulation (ppm/g dry weight) in pods and seeds (d), and histological localization of Cd ions as Cd-oxalate white crystals in stem tissue transverse sections, Cd alone (f,g) and GA3 pus Cd (e,h) of mung bean plants grown in soil in pots at time of harvest. Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates) for (a–c). Scale bars: 1000 µm for (e,f) and 100 µm for (g,h). Red circles and red arrows represent the localization of Cd oxalate crystals. Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Figure 4. Effect of GA3 on accumulation, translocation, and localization of cadmium (Cd) in mung bean plants. Effect of GA3 on cadmium (Cd) accumulation (ppm/g dry weight) in leaf, shoot, and root tissue (a), bioaccumulation factor (BAF, Cd accumulation root/soil) (b), translocation factor (shoot/root and leaf/shoot) (c), Cd accumulation (ppm/g dry weight) in pods and seeds (d), and histological localization of Cd ions as Cd-oxalate white crystals in stem tissue transverse sections, Cd alone (f,g) and GA3 pus Cd (e,h) of mung bean plants grown in soil in pots at time of harvest. Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates) for (a–c). Scale bars: 1000 µm for (e,f) and 100 µm for (g,h). Red circles and red arrows represent the localization of Cd oxalate crystals. Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
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Figure 5. Effect of GA3 on the relative gene expression of Vigna radiata phytochelatin synthase 1 (VrPCS1), (a), VrIron transporter 1 (VrIRT1) (b), VrIron transporter 2 (VrIRT2) (c) and Vr cadmium response (VrCDR29) (d) in young seedlings subjected to Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions in paper roll method. Data presented are means ± standard errors (n = 3, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Figure 5. Effect of GA3 on the relative gene expression of Vigna radiata phytochelatin synthase 1 (VrPCS1), (a), VrIron transporter 1 (VrIRT1) (b), VrIron transporter 2 (VrIRT2) (c) and Vr cadmium response (VrCDR29) (d) in young seedlings subjected to Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions in paper roll method. Data presented are means ± standard errors (n = 3, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
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Figure 6. Effect of GA3 on pod and seed size attributes under Cd stress. Control (CN, (a,b)), Cd stress (Cd, (c,d)), GA3 (e,f) and Cd+ GA3 (g,h) conditions.
Figure 6. Effect of GA3 on pod and seed size attributes under Cd stress. Control (CN, (a,b)), Cd stress (Cd, (c,d)), GA3 (e,f) and Cd+ GA3 (g,h) conditions.
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Figure 7. Effect of GA3 with or without cadmium (Cd) stress on pod length (a), pod diameter (b), pod number/plant (c), pod fresh weight/plant (Pod FW, d), pod dry weight (Pod DW, e), normal and aborted seed number/ten pods (f), hundred seeds weight (g), seed weight/pod (h), seed surface area(SA) (i) and seed sugar (j) of mung bean plants grown in soil in pots at time of harvest. Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Figure 7. Effect of GA3 with or without cadmium (Cd) stress on pod length (a), pod diameter (b), pod number/plant (c), pod fresh weight/plant (Pod FW, d), pod dry weight (Pod DW, e), normal and aborted seed number/ten pods (f), hundred seeds weight (g), seed weight/pod (h), seed surface area(SA) (i) and seed sugar (j) of mung bean plants grown in soil in pots at time of harvest. Control (CN), cadmium (Cd) stress, Cd+ gibberellins (GA3), and GA3 alone conditions. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
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Table
Table 1. Effect of cadmium (Cd) stress with or without gibberellins (GA3) on the physiological attributes of Vigna radiata L. on chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (CAR), total soluble sugars (TSS) in mg g−1 fresh weight, malondialdehyde (MDA, µmol g−1 fresh weight), proline (PL), total phenol content (TPC), protein (Prot) content in mg g−1 fresh weight, urease activity (UA, µg NH3 g−1 15 min−1) and nodule leg hemoglobin content (Leg Hb, mg g−1 fresh weight) in leaf tissues subjected to control (CN), cadmium stress (Cd), gibberellins (GA3), Cd+GA3 at 30 days after sowing (DAS), 45 DAS, 60 DAS, and 75 DAS.
Table 1. Effect of cadmium (Cd) stress with or without gibberellins (GA3) on the physiological attributes of Vigna radiata L. on chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (CAR), total soluble sugars (TSS) in mg g−1 fresh weight, malondialdehyde (MDA, µmol g−1 fresh weight), proline (PL), total phenol content (TPC), protein (Prot) content in mg g−1 fresh weight, urease activity (UA, µg NH3 g−1 15 min−1) and nodule leg hemoglobin content (Leg Hb, mg g−1 fresh weight) in leaf tissues subjected to control (CN), cadmium stress (Cd), gibberellins (GA3), Cd+GA3 at 30 days after sowing (DAS), 45 DAS, 60 DAS, and 75 DAS.
ChlaChlbCARTSSMDAPLTPCProtUrease ActivityLeg Hb
CN30DAS4.98 ± 0.29 a1.03 ± 0.06 a1.02 ± 0.06 a9.2 ± 0.55 a0.63 ± 0.03 a2.83 ± 0.14 a1.65 ± 0.08 a1.36 ± 0.06 a7.22 ± 0.36 a1.26 ± 0.29 a
45DAS6.21 ± 0.37 a1.38 ± 0.08 a1.96 ± 0.11 a12.51 ± 0.751.23 ± 0.06 a3.56 ± 0.17 a2.56 ± 0.12 a1.59 ± 0.07 a8.60 ± 0.43 a2.54 ± 0.08 a
60DAS6.77 ± 0.40 a1.40 ± 0.08 a2.03 ± 0.12 a20.02 ± 1.201.54 ± 0.07 a4.65 ± 0.23 a3.66 ± 0.18 a2.34 ± 0.11 a7.02 ± 0.35 a4.93 ± 0.07 b
75DAS6.42 ± 0.38 a3.41 ± 0.20 a1.75 ± 0.10 a20.36 ± 1.221.88 ± 0.09 a6.56 ± 0.32 a4.56 ± 0.22 a3.20 ± 0.16 a4.02 ± 0.20 a6.09 ± 0.19 b
Cd30DAS2.25 ± 0.13 b2.63 ± 0.15 b1.62 ± 0.09 b5.2 ± 0.310.85 ± 0.04 b8.56 ± 0.42 b1.99 ± 0.09 a3.58 ± 0.17 b6.74 ± 0.33 a0.79 ± 0.03 a
45DAS3.55 ± 0.21 b2.28 ± 0.13 b2.02 ± 0.12 a7.26 ± 0.431.65 ± 0.08 b10.56 ± 0.52 b2.56 ± 0.12 a2.15 ± 0.10 b5.47 ± 0.27 b2.69 ± 0.17 b
60DAS3.42 ± 0.20 b4.58 ± 0.27 b2.59 ± 0.15 b9.42 ± 0.562.88 ± 0.14 b17.23 ± 0.86 b4.56 ± 0.22 b3.22 ± 0.16 b4.91 ± 0.24 b2.14 ± 0.04 b
75DAS3.81 ± 0.22 b3.58 ± 0.21 a1.75 ± 0.10 a11.96 ± 0.713.01 ± 0.15 b19.36 ± 0.96 b5.66 ± 0.28 a3.06 ± 0.15 a4.52 ± 0.22 a2.77 ± 0.29 b
Cd+GA330DAS3.94 ± 0.23 c4.00 ± 0.24 c1.63 ± 0.095.6 ± 0.33 b0.72 ± 0.03 a15.23 ± 0.76 d1.89 ± 0.09 b1.42 ± 0.07 a10.01 ± 0.5 b0.91 ± 0.03 a
45DAS3.97 ± 0.23 b3.41 ± 0.20 c2.84 ± 0.17 b8.50 ± 0.511.35 ± 0.06 a19.65 ± 0.98 d2.44 ± 0.12 a2.45 ± 0.12 b9.54 ± 0.47 a2.68 ± 0.08 b
60DAS4.25 ± 0.25 b3.51 ± 0.21 c3.17 ± 0.19 c18.93 ± 1.132.14 ± 0.10 c20.12 ± 1.00 b3.66 ± 0.18 a3.77 ± 0.18 c9.35 ± 0.46 c6.04 ± 0.58 c
75DAS4.26 ± 0.25 d4.09 ± 0.24 c2.90 ± 0.17 b21.67 ± 1.32.04 ± 0.10 a21.36 ± 1.06 b4.33 ± 0.21 a2.70 ± 0.13 b5.12 ± 0.25 c8.16 ± 0.42 d
GA330DAS5.90 ± 0.35 a2.67 ± 0.16 b3.39 ± 0.208.7 ± 0.52 c0.84 ± 0.04 b4.56 ± 0.22 c2.15 ± 0.10 b1.78 ± 0.08 a7.97 ± 0.39 a1.02 ± 0.04 a
45DAS6.44 ± 0.38 a3.30 ± 0.19 b2.49 ± 0.14 b11.55 ± 0.691.65 ± 0.08 b5.60 ± 0.28 c2.66 ± 0.13 a2.19 ± 0.10 b7.52 ± 0.37 a4.02 ± 0.29 b
60DAS7.25 ± 0.43 a2.62 ± 0.15 c2.37 ± 0.14 a26.6 ± 1.592.00 ± 0.10 a12.56 ± 0.62 c3.36 ± 0.16 a3.63 ± 0.18 b7.66 ± 0.38 a5.42 ± 0.15 c
75DAS7.72 ± 0.46 c5.73 ± 0.34 b1.88 ± 0.11 b31.24 ± 1.872.15 ± 0.10 a16.23 ± 0.81 b4.56 ± 0.22 a3.56 ± 0.17 a7.85 ± 0.39 b4.58 ± 0.16 b
Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations with respective days after sowing (Tukey’s test, p ≤ 0.05).
Table
Table 2. Effect of cadmium (Cd) stress with or without gibberellins (GA3) on seed geometric attributes viz. width (W), length (L), thickness (T), Sphericity (S), Ew, Ev, geometric mean (Dg), seed shape (Φ%), volume of the grain (V), gravity (%G), seed protein content (SPr, mg g−1 dry weight) and seed total phenol content (STPC, mg g−1 dry weight) of seeds of mung bean plants subjected to control (CN), cadmium stress (Cd), gibberellins (GA3), Cd+GA3 at 30 days after sowing (DAS), 45 DAS, 60 DAS, and 75 DAS. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
Table 2. Effect of cadmium (Cd) stress with or without gibberellins (GA3) on seed geometric attributes viz. width (W), length (L), thickness (T), Sphericity (S), Ew, Ev, geometric mean (Dg), seed shape (Φ%), volume of the grain (V), gravity (%G), seed protein content (SPr, mg g−1 dry weight) and seed total phenol content (STPC, mg g−1 dry weight) of seeds of mung bean plants subjected to control (CN), cadmium stress (Cd), gibberellins (GA3), Cd+GA3 at 30 days after sowing (DAS), 45 DAS, 60 DAS, and 75 DAS. Data presented are means ± standard errors (n = 10, biological replicates). Different letters (a, b, c) indicate significant differences from control in all combinations (Tukey’s test, p ≤ 0.05).
TreatmentWLTSEwEvDgΦ%V%GSPrSTPC
CN3.94 ± 0.13 a4.85 ± 0.20 a3.95 ± 0.27 a17.27 a1.23 a0.99 a4.21 ± 0.25 a86.76 a39.7695 a1.08 a ± 0.010.63 ± 0.002
Cd3.42 ± 0.24 b4.12 ± 0.66 b3.40 ± 0.26 b14.46 b1.20 a1.00 a3.63 ± 0.21 b87.97 a25.4952 b0.69 b ± 0.0022.17 ± 0.025
Cd+GA33.71 ± 0.24 a4.75 ± 0.48 a3.68 ± 0.23 a16.38 a1.28 b1.00 a4.01 ± 0.24 a84.39 a34.3678 c0.55 b ± 0.0010.17 ± 0.001
GA33.60 ± 0.24 a4.51 ± 0.33 a3.55 ± 0.17 b15.65 a1.25 a1.01 a3.86 ± 0.23 a85.57 a30.6597 a0.70 a ± 0.0010.36 ± 0.001
Table
Table 3. Pearson correlation coefficient (r) for ten traits of plant fitness (stem height, stem diameter, leaf number, leaf surface area, and root length) and of agronomical attributes (seed number, seed weight, seed weight/pod, seed surface area) for Control versus Cd, Control versus Cd+GA3 and Control versus GA3.
Table 3. Pearson correlation coefficient (r) for ten traits of plant fitness (stem height, stem diameter, leaf number, leaf surface area, and root length) and of agronomical attributes (seed number, seed weight, seed weight/pod, seed surface area) for Control versus Cd, Control versus Cd+GA3 and Control versus GA3.
Pearson Correlation for Morphometeric Traits
Stem HeightStem DiameterLeaf NumberLeaf Surface AreaRoot Length
CN11111
Cd0.3640.593 *0.0140.447−0.289
Cd+GA3−0.0500.8750.582 *−0.0610.473
Pearson Correlation for Agronomic Traits
Seed NumberSeed WeightSeed Weight/PodSeed Surface Area
CN1111
Cd0.1270.0750.295−0.156
Cd+GA30.088−0.413−0.400−0.032
Number of biological replicates (n = 13) across treatments. Asterisk * represents whether the correlation is significant at the 0.05 level (2-tailed).
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Hakla, H.R.; Sharma, S.; Urfan, M.; Yadav, N.S.; Rajput, P.; Kotwal, D.; Abdel Latef, A.A.H.; Pal, S. Gibberellins Target Shoot-Root Growth, Morpho-Physiological and Molecular Pathways to Induce Cadmium Tolerance in Vigna radiata L. Agronomy 2021, 11, 896. https://doi.org/10.3390/agronomy11050896

AMA Style

Hakla HR, Sharma S, Urfan M, Yadav NS, Rajput P, Kotwal D, Abdel Latef AAH, Pal S. Gibberellins Target Shoot-Root Growth, Morpho-Physiological and Molecular Pathways to Induce Cadmium Tolerance in Vigna radiata L. Agronomy. 2021; 11(5):896. https://doi.org/10.3390/agronomy11050896

Chicago/Turabian Style

Hakla, Haroon Rashid, Shubham Sharma, Mohammad Urfan, Narendra Singh Yadav, Prakriti Rajput, Dinesh Kotwal, Arafat Abdel Hamed Abdel Latef, and Sikander Pal. 2021. "Gibberellins Target Shoot-Root Growth, Morpho-Physiological and Molecular Pathways to Induce Cadmium Tolerance in Vigna radiata L." Agronomy 11, no. 5: 896. https://doi.org/10.3390/agronomy11050896

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