Search Results (13)

Zinc (Zn) deficiency poses a major global health challenge, and wheat grains generally contain low Zn concentrations. In this study, the wheat cultivar ‘Zhongmai 175’ was identified as zinc-efficient. Hydroponic experiments demonstrated that Zn deficiency induced the secretion of oxalic acid and malic acid in root exudates and significantly increased total root length in ‘Zhongmai 175’. To elucidate the underlying regulatory mechanisms, transcriptome profiling via RNA sequencing was conducted under Zn-deficient conditions. A total of 2287 and 1935 differentially expressed genes (DEGs) were identified in roots and shoots, respectively. Gene Ontology enrichment analysis revealed that these DEGs were primarily associated with Zn ion transport, homeostasis, transmembrane transport, and hormone signaling. Key DEGs belonged to gene families including VIT, NAS, DMAS, ZIP, tDT, HMA, and NAAT. KEGG pathway analysis indicated that phenylpropanoid biosynthesis, particularly lignin synthesis genes, was significantly downregulated in Zn-deficient roots. In shoots, cysteine and methionine metabolism, along with plant hormone signal transduction, were the most enriched pathways. Notably, most DEGs in shoots were associated with the biosynthesis of phytosiderophores (MAs, NA) and ethylene. Overall, genes involved in Zn ion transport, phytosiderophore biosynthesis, dicarboxylate transport, and ethylene biosynthesis appear to play central roles in wheat’s adaptive response to Zn deficiency. These findings provide a valuable foundation for understanding the molecular basis of Zn efficiency in wheat and for breeding Zn-enriched varieties. Full article

Low-molecular-weight organic acids (LMWOAs) are essential O-containing metal-binding ligands involved in maintaining metal homeostasis, various metabolic processes, and plant responses to biotic and abiotic stress. Malate, citrate, and oxalate play a crucial role in metal detoxification and transport throughout the plant. This review provides a comparative analysis of the accumulation of LMWOAs in excluders, which store metals mainly in roots, and hyperaccumulators, which accumulate metals mainly in shoots. Modern concepts of the mechanisms of LMWOA secretion by the roots of excluders and hyperaccumulators are summarized, and the formation of various metal complexes with LMWOAs in the vacuole and conducting tissues, playing an important role in the mechanisms of metal detoxification and transport, is discussed. Molecular mechanisms of transport of LMWOAs and their complexes with metals across cell membranes are reviewed. It is discussed whether different endogenous levels of LMWOAs in plants determine their metal tolerance. While playing an important role in maintaining metal homeostasis, LMWOAs apparently make a minor contribution to the mechanisms of metal hyperaccumulation, which is associated mainly with root exudates increasing metal bioavailability and enhanced xylem loading of LMWOAs. The studies of metal-binding compounds may also contribute to the development of approaches used in biofortification, phytoremediation, and phytomining. Full article

Magnesium (Mg) plays a crucial role in crop growth, but how Mg supply level affects root growth and nutrient absorption in vegetable crops with different genotypes has not been sufficiently investigated. In this study, the responses of tomato (Solanum lycopersicum L.) and cucumber (Cucumis sativus L.) crops to different levels of Mg supply were explored. Four levels of Mg treatment (i.e., 0.2, 1.0, 2.0, 3.0 mmol/L) were applied under hydroponic conditions, denoted as Mg0.2, Mg1, Mg2, and Mg3, respectively. The results showed that with increasing Mg levels, the plant biomass, root growth, and nutrient accumulation in both vegetable crops all increased until reaching their maximum values under the Mg2 treatment and then decreased. The total biomass per tomato plant of Mg2 treatment was 30.9%, 14.0%, and 14.0% higher than that of Mg0.2, Mg1, and Mg3 treatments, respectively, and greater increases were observed in cucumber plant biomass (by 54.3%, 17.4%, and 19.9%, respectively). Compared with the Mg0.2 treatment, the potassium (K) and calcium (Ca) contents in various plant parts of both crops remarkably decreased under the Mg3 treatment. This change was accompanied by prominently increased Mg contents in various plant parts and para-hydroxybenzoic acid and oxalic acid contents in root exudates. Irrespective of Mg level, plant biomass, root growth, nutrient accumulation, and root exudation of organic acids were all higher in tomato plants than in cucumber plants. Our findings indicate that excessive Mg supply promotes the roots to exude phenolic acids and hinders the plants from absorbing K and Ca in different genotypes of vegetable crops despite no effect on Mg absorption. A nutritional deficiency of Mg stimulates root exudation of organic acids and increases the types of exuded organic acids, which could facilitate plant adaption to Mg stress. In terms of root growth and nutrient absorption, tomato plants outperform cucumber plants under low and medium Mg levels, but the latter crop is more tolerant to Mg excess. Full article

Root exudates are tightly linked with cadmium (Cd) uptake by the root and thus affect plant Cd accumulation. A hydroponic experiment was carried out to explore the role of root exudates in Cd accumulation of a low-Cd-accumulating tobacco line (RG11) compared with a high-Cd- accumulating tobacco line (Yuyan5). Greater secretion of organic acids and amino acids by the roots was induced by an exogenous Cd addition in the two tobacco lines. The concentration of organic acid secreted by RG11 was only 51.1~61.0% of that secreted by Yuyan5. RG11 roots secreted more oxalic acid and acetic acid and less tartaric acid, formic acid, malic acid, lactic acid, and succinic acid than Yuyan5 under Cd stress. Oxalic acid accounted for 26.8~28.8% of the total organic acids, being the most common component among the detected organic acids, and was significantly negatively correlated with Cd accumulation in RG11. Propionic acid was only detected in the root exudates of RG11 under Cd stress. Lactic acid was positively linked with Cd accumulation in Yuyan5, being less accumulated in RG11. Similarly, RG11 secreted more amino acids than Yuyan5 under Cd stress. Aspartic acid, serine, and cysteine appeared in RG11 when it was exposed to Cd. Lysine was the most secreted amino acid in RG11 under Cd stress. RG11 roots secreted less lysine, histidine, and valine, but more phenylalanine and methionine than Yuyan5 under Cd stress. The results show that organic acids and amino acids in root exudates play a key role in Cd uptake by the root, and this contribution varied with cultivar/genotype. However, further research is still needed to explore the mechanisms underlying low Cd translocation to the leaf, which may be the key contribution of low Cd accumulation in RG11 to the security of tobacco leaf. Full article

Alfalfa (Medicago sativa L.) is an important legume forage, and phosphorus is a significant nutrient element of alfalfa with high quality and high yield. However, the effect mechanism of different phosphorus application rates on soil bacteria, and the phosphorus efficiency of alfalfa are still unclear. Therefore, we present the results of a study in which alfalfa was inoculated with Funneliformis mosseae, Bacillus megaterium, double inoculated with Funneliformis mosseae and Bacillus megaterium, and given no inoculation bacteria. P₂O₅ was applied under the condition of bacterial inoculation, and the contents were 0, 50, 100, and 150 mg kg⁻¹, respectively, to explore the effect of bacterial inoculation on alkaline phosphatase, organic acid, pH, organic matter, and the relationship between the indicators in alfalfa soil, under different phosphorus application rates. The effect of mixed inoculation was significantly higher than that of the non-inoculated control group (p < 0.05). The organic matter content of rhizosphere soil was higher than that of non-rhizosphere soil. When the phosphorus application rate was 100 mg kg⁻¹, the content of alkaline phosphatase in the soil inoculated with Funneliformis mosseae and Bacillus megaterium was better than that in the single inoculation, and no inoculation. Principal component analysis showed that the top three treatments were: double inoculation bacteria and treatment group with phosphorus application rate of 100 mg kg⁻¹ >; double inoculation bacteria and treatment group with phosphorus application rate of 50 mg kg⁻¹ >; double inoculation bacteria and treatment group with phosphorus application rate of 150 mg kg⁻¹. In addition, when P₂O₅ was 100 mg kg⁻¹, the addition of Funneliformis mosseae and Bacillus megaterium to alfalfa soil could increase the content of organic matter in the soil, promote the metabolism of alfalfa root exudates, and increase the organic acid of the rhizosphere soil, compared with the control without inoculation, and without phosphorus application. At the same time, the phosphatase activity in the soil had a significant positive correlation with malic acid, oxalic acid, acetic acid, total organic acid, and soil pH, thereby improving soil fertility and promoting phosphorus absorption by plants. These findings provide new insights into alfalfa root soils and the effects of Funneliformis mosseae and Bacillus megaterium additions on soil nutrients. Full article

A significant proportion of the carbon fixed by plants is transported to the roots and exuded to the rhizosphere. Exudates may have important roles in the rhizosphere, such as desorbing labile phosphorus (P) or mobilizing manganese (Mn) and other metal cations. This study evaluated the root exudation profiles of seedlings of 15 eucalypt species in response to a P shortage and if the ability to exude organic compounds was related to P and Mn accumulation in the shoots. The plants were grown on sand and were irrigated with nutrient solutions containing either sufficient P (500 µM) or low P (25 µM). Organic acids (OA), amino acids/polyamines, and phenolics were analyzed in the root exudates by UPLC-MS/MS. Plants with a low P level had low leaf P contents and growth reduction. A P shortage induced the exudation of the three groups of metabolites analyzed at higher levels than sufficient P availability. Despite that, the composition pattern of root exudates was similar among species under low or sufficient P concentrations. Citric and isocitric acids were the major OAs found in the exudates, followed by oxalic, malic, and succinic acids. Among the amino acids/polyamines identified, putrescine was the most abundant in all species, followed by glycine. Cinnamic acid was the predominant phenolic in the root exudates. Our results indicate that P limitation induces a conserved response genetic mechanism in eucalypts. Such results can be further investigated to adapt commercial clones to soils with low P availability. Full article

Ethnobotanical studies have reported the traditional medicinal uses of Acacia senegal (L.) Willd. and Argania spinosa (L.) Skeels against kidney stone formation and other chronic kidney diseases. The present work is undertaken to study the litholytic activity and the inhibiting activity of calcium oxalate crystallization by bioactive compounds identified in Argania spinosa (L.) Skeels press-cake (residue of Argan oil) and in Acacia senegal (L.) Willd. The litholytic activity was studied in vitro on cystine and uric acid stones using a porous bag and an Erlenmeyer glass. The study of the inhibiting activity of calcium oxalate crystallization, was based on temporal measurements of the optical density, registered at a 620 nm wavelength for 30 min using an ultraviolet–visible spectrophotometer. The silylation method was performed to identify phytochemicals, followed by gas chromatography coupled with mass spectrophotometry (GC/MS) analysis. The results show significant litholytic activity of Argania Spinosa press-cake hydro-ethanolic extract on uric acid and cystine stones, respectively, with dissolution rates (DR) of 86.38% and 60.42% versus 3.23% and 9.48% for the hydro-ethanolic extract of Acacia senegal exudate. Furthermore, the percentages of nucleation inhibition are 83.78% and 43.77% (p ˂ 0.05) for Argania spinosa and Acacia senegal, respectively. The results point to the detection of 17 phytochemicals in Argania spinosa press-cake extract, the majority of which are phenolic acids and have potent anti-urolithiatic action. Full article

In rhizospheric soil, arsenic can be activated by both biological and abiotic reactions with plant exudates or phosphates, but little is known about the relative contributions of these two pathways. The effects of microorganisms, low-molecular-weight organic acid salts (LMWOASs), and phosphates on the migration of As in unrestored and nano zero-valent iron (nZVI)-restored soil were studied in batch experiments. The results show that As released by microbial action accounted for 17.73%, 7.04%, 92.40%, 92.55%, and 96.68% of the total As released in unrestored soil with citrate, phytate, malate, lactate, and acetate, respectively. It was only suppressed in unrestored soil with oxalate. In restored soil, As was still released in the presence of oxalate, citrate, and phytate, but the magnitude of As release was inhibited by microorganisms. The application of excess nZVI can completely inhibited As release processes induced by phosphate in the presence of microorganisms. Microbial iron reduction is a possible mechanism of arsenic release induced by microorganisms. Microorganisms and most environmental factors promoted As release in unrestored soil, but the phenomenon was suppressed in restored soil. This study helps to provide an effective strategy for reducing the secondary release of As from soils due to replanting after restoration. Full article

Potassium (K) reduces the deleterious effects of drought stress on plants. However, this mitigation has been studied mainly in the aboveground plant pathways, while the effect of K on root-soil interactions in the underground part is still underexplored. Here, we conducted the experiments to investigate how K enhances plant resistance and tolerance to drought by controlling rhizosphere processes. Three culture methods (sand, water, and soil) evaluated two rapeseed cultivars’ root morphology, root exudates, soil nutrients, and microbial community structure under different K supply levels and water conditions to construct a defensive network of the underground part. We found that K supply increased the root length and density and the organic acids secretion. The organic acids were significantly associated with the available potassium decomposition, in order of formic acid > malonic acid > lactic acid > oxalic acid > citric acid. However, the mitigation had the hormesis effect, as the appropriate range of K facilitated the morphological characteristic and physiological function of the root system with increases of supply levels, while the excessive input of K could hinder the plant growth. The positive effect of K-fertilizer on soil pH, available phosphorus and available potassium content, and microbial diversity index was more significant under the water stress. The rhizosphere nutrients and pH further promoted the microbial community development by the structural equation modeling, while the non-rhizosphere nutrients had an indirect negative effect on microbes. In short, K application could alleviate drought stress on the growth and development of plants by regulating the morphology and secretion of roots and soil ecosystems. Full article

Optimisation of potassium (K) use efficiency in pastures on sandy soil is challenging. We characterised growth response, root carboxylate exudation and mycorrhizal colonisation in three perennial pasture grasses: tall fescue (Festuca arundinacea L.), veldt grass (Ehrharta calycina Sm.) and tall wheatgrass (Thinopyrum ponticum L.) in two glasshouse experiments with: (1) four K rates (0, 40, 80 and 120 mg K kg^-1 soil), and (2) four N and K treatments (no N and K (–N–K), 81 mg N kg^-1 soil but no K, 80 mg K kg^-1 soil but no N, and N at 81 and K at 80 mg kg^-1 soil (+N+K)) in low-K sandy soil. Veldt grass had the highest shoot dry weight and shoot P content, but the lowest mycorrhizal colonisation. Potassium fertilisation had no significant impact on exudation of citrate and oxalate. The K0 plants had significantly lower exudation of acetate and total carboxylates than K40 plants. The +N+K plants had maximum shoot growth at both harvests (30 and 60 days after sowing (DAS)) and highest N and K shoot contents at 60 DAS. The –N–K plants exuded maximum amounts of citrate and malate at 30 DAS, but at 60 DAS tall fescue had the highest rhizosphere concentrations of citrate and malate in the +N+K treatment. At 60 DAS, mycorrhizal colonisation was significantly lower with than without N and K fertilisation. We concluded that pasture grasses could yield well even in inherently low-K soil without external K fertilisation and mycorrhizal symbiosis. However, the +N+K plants had the highest yield and root carboxylate exudation. Full article

The rhizosphere is an essential pathway for the uptake of metal-based nanoparticles (MNPs) by plant roots. However, the interaction between root exudates and MNPs is still unclear. In this study, we initially identified the major low-molecular-weight organic acids (LMWOAs) in the rice root exudates using hydroponics. Then, the individual LMWOAs were added to CuO nanoparticle suspensions to investigate their effects on the environmental behavior of the MNPs. The results showed that both the variety and the concentration of LMWOAs impacted the aggregation, sedimentation, and dissolution of CuO nanoparticles (NPs). Almost all LMWOAs except succinic acid inhibited the aggregation of CuO NPs by enhancing the electrostatic repulsive force between NPs. The presence of citric and oxalic acids rather than lactic acid greatly improved the stability of CuO NP suspensions, but other acids showed a low promoting and high inhibiting effect on NP sedimentation. Moreover, all the LMWOAs from root exudates facilitated the dissolution of CuO NPs with a positive dose-dependent correlation, especially formic acid. Notably, citric acid, as the most abundant LMWOAs in rice root exudates, largely determined the aggregation, sedimentation, and dissolution of CuO NPs. This study provides a better understanding on NP–plant interactions in the rhizosphere. Full article

Carboxylate efflux from roots is a crucial and differential response of soybean genotypes to low phosphorus (P) stress. Exudation of carboxylic acids including oxalate, citrate, succinate and fumarate was induced under low P stress, particularly in P-efficient soybean genotypes. Enhancement of root length, surface area and volume further improved P acquisition under low P stress. To understand the molecular basis of carboxylate efflux under low P stress, the root proteome of contrasting genotypes (P-efficient: EC-232019 and P-inefficient: EC-113396) was compared. Among a total of 325 spots, 105 (32%) were differentially abundant proteins (DAPs) between sufficient (250 µM) and low P (4 µM) levels. Abundance of 44 (14%) proteins decreased by more than two-fold under low P stress, while 61 (19%) proteins increased by more than two-fold. Protein identification and annotation revealed that the DAPs were involved in a myriad of functions including carboxylic acid synthesis, carbohydrate, protein and lipid metabolism. Proteins with significant abundance included malate dehydrogenase, isocitrate dehydrogenase, phosphoglucomutase, phosphoglycerate mutase, fructokinase, enolase, phosphoglycerate kinase, triosephosphate isomerase, alcohol dehydrogenase, glucan water dikinase, glutamine synthetase and argininosuccinate lyase. Inferences from proteomic analysis suggests the crosstalk between various metabolic pathways implicated in conferring superior P acquisition efficiency under stress. Full article

Aluminium (Al) toxicity is a major factor reducing crop productivity worldwide. There is a broad variation in intra- and inter-specific Al resistance. Whereas the Al resistance mechanisms have generally been well explored in Al-excluding plant species, Al resistance through Al accumulation and Al tolerance is not yet well understood. Therefore, a set of 94 genotypes from three Fagopyrum species with special emphasis on F. esculentum Moench were screened, with the objective of identifying genotypes with greatly differing Al accumulation capacity. The genotypes were grown in Al-enriched peat-based substrate for 21 days. Based on the Al concentration of the xylem sap, which varied by a factor of five, only quantitative but not qualitative genotypic differences in Al accumulation could be identified. Aluminium and citrate and Al and Fe concentrations in the xylem sap were positively correlated suggesting that Fe and Al are loaded into and transported in the xylem through related mechanisms. In a nutrient solution experiment using six selected F. esculentum genotypes differing in Al and citrate concentrations in the xylem sap the significant correlation between Al and iron transport in the xylem could be confirmed. Inhibition of root elongation by Al was highly significantly correlated with root oxalate-exudation and leaf Al accumulation. This suggests that Al-activated oxalate exudation and rapid transport of Al to the shoot are prerequisites for the protection of the root apoplast from Al injury and thus overall Al resistance and Al accumulation in buckwheat. Full article