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Article

Physiological Mechanisms of Drought-Induced Creasing in Citrus unshiu Marc: Roles of Antioxidant Dysregulation, Hormonal Imbalance, Cell Wall Degradation, and Mineral Redistribution

by
Wei Hu
,
Woxing Fu
,
Dechun Liu
,
Zhonghua Xiong
,
Li Yang
,
Liuqing Kuang
,
Jie Song
,
Jingheng Xie
and
Yong Liu
*
College of Agronomy, Jiangxi Agricultural University, Nanchang 330045, China
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(10), 1197; https://doi.org/10.3390/horticulturae11101197
Submission received: 21 August 2025 / Revised: 16 September 2025 / Accepted: 30 September 2025 / Published: 3 October 2025
(This article belongs to the Special Issue New Insights into Breeding and Genetic Improvement of Fruit Crops)
Browse Figures
Versions Notes

Abstract

Citrus creasing is a physiological rind disorder. Satsuma mandarin (Citrus unshiu Marc.) is the most widely cultivated mandarin variety worldwide and exhibits a high susceptibility to creasing. To investigate the physiological mechanisms underlying creasing, satsuma mandarin trees were treated with different drought stress during fruit expansion, then the relationship between the soil water content and creasing incidence was analyzed, while also examining the rind morphology, oil gland distribution in the flavedo, antioxidant enzyme activities, hormone concentrations, cell wall components, mineral content of creasing fruit, and the impact of creasing on fruit quality. Results showed that severe water stress (35% SRWC) increased the creasing incidence rate by 28% compared to well-irrigated treatments (80% SRWC). The creasing fruit oil gland diameter reduced by 35.7% and the density increased by 149.7% compared to healthy fruits. Simultaneously, the content of H2O2 and proline elevated by 47.1% and 8.3% respectively, and the activities of SOD, POD, and CAT of the creasing rind were enhanced significantly. Additionally, the content of IAA, ZR, and MeJA decreased by 17.2%, 7.8%, and 50.2%, respectively. Cell wall components such as cellulose, hemicellulose, and protopectin content reduced by 44.6%, 31.7%, and 33.1%, while soluble pectin increased by 36.3%. Significant alterations were observed in several minerals (Al, Fe, Na, Ni, V, Ga, Zn, Ba, Sn, Hg, Sc, Y, and La). However, fruit quality remained unaffected by creasing. These results demonstrate that drought is a key factor inducing creasing. Increased oil gland density, the degradation of cell wall components, elevated oxidative stress, reductions in phytohormones, and altered mineral element content work together to contribute to rind cells’ structural instability and lead to creasing in the satsuma mandarin.

1. Introduction

The genus citrus is an economically significant fruit crop, valued for its nutritional richness and as a primary source of vitamin C [1]. Cultivated extensively worldwide, China is one of the largest citrus-producing countries [2]. Citrus creasing, a physiological disorder characterized by the breakdown of the albedo and uneven fruit surface, compromises the external quality and reduces postharvest storage and transport potential [3]. This disorder occurs across citrus varieties including the sweet orange (Citrus sinensis (L.) Osbeck), Shatangju mandarin (Citrus reticulata Blanco cv. Shatangju), Clementine (Citrus clementina hort. ex Tanaka), and satsuma mandarin (Citrus unshiu Marc.), with reported yield losses exceeding 50% [3]. Previous studies explored creasing control via foliar applications of calcium [4,5], gibberellins [6,7], aminoethoxyvinylglycine (AVG) [8], polyamines [9], and combined zinc–NAA (Naphthalene acetic acid) treatments [10]. Although these methods reduced the creasing incidence, their efficacy remains suboptimal, often causing adverse effects such as thickened rinds, delayed coloration, and uneven pigmentation. Therefore, elucidating the physiological basis of rind creasing is critical for developing effective mitigation strategies.
Rind creasing is closely associated with the loss of structural integrity in the rind. Previous studies implicated varietal differences, rind thickness, water stress, and mineral imbalance as key factors [3,7], though inconsistent correlations exist. Jones first reported that creasing in the sweet orange arises from cell wall degradation in the albedo, leading to the collapse of the flavedo [11]. Similarly, reduced protopectin and cellulose contents weakened the cell walls in the creasing-affected ‘Hong Jiang’ sweet orange [12]. In ‘Washington Navel’ and ‘Navelina’ oranges, creasing coincided with decreased protopectin, increased soluble pectin, and elevated activities of cell wall-degrading enzymes (pectinesterase, PE; polygalacturonase, PG; and endo-1,4-ß-D-glucanase, EGase) [13]. Other rind disorders like puffing and cracking also correlate with cell wall degradation, reactive oxygen species (ROS) accumulation, antioxidant enzyme activities, and phytohormonal imbalances [14,15,16]. Mineral elements further influence creasing development. Potassium (K) and calcium (Ca) levels in the ‘Hong Jiang’ orange positively and negatively correlated with creasing incidences, respectively [17]. Molybdenum (Mo) and sulfur (S) significantly affected creasing in South African ‘Washington Navel’ orchards whereas Ca showed limited impact, and N, P, K, Mg, Mn, B, Cu, Fe, and Zn exhibited no effects [18]. Contrastingly, creasing in ‘Washington Navel’ and ‘Valencia’ oranges showed no correlation with the rind minerals of mature fruits but was linked to copper (Cu), K, and Mn concentrations during fruit development [7].
Mandarins dominate China’s citrus production, with the satsuma mandarin being the primary cultivar [19]. Despite its susceptibility to creasing, physiological studies have focused predominantly on sweet oranges, leaving the satsuma mandarin’s physiological creasing mechanism poorly researched. This study investigated the quantitative relationship between the soil water deficit and creasing incidence in the ‘Miyagawa Wase’ satsuma mandarin, the creasing-related alterations in oil gland morphology, antioxidant enzymes, phytohormones, cell wall metabolites, and mineral redistribution to elucidate the physiological mechanism underlying rind creasing in satsuma mandarin.

2. Materials and Methods

2.1. Plant Material and Drought Treatments

Twelve-year-old satsuma mandarin (Citrus unshiu Marc. Miyagawa) trees, grafted onto trifoliate orange (Citrus trifoliata) rootstocks and cultivated under greenhouse conditions in Xinggan County, Jiangxi Province, China, were selected for uniformity in growth vigor and fruit load. The experimental area featured red soil with pH 4.6, the average annual temperature is 17.5 °C, and the average annual rainfall is 1604.5 mm.
At the fruit expansion stage (30~90 DAF), Tyvek® non-woven mulch was applied to ridges and furrows to stabilize soil moisture content. Four soil relative water content (SRWC) gradients were initiated at 146 days after flowering (DAF): SRWC 80% (sufficient irrigation), SRWC 65% (mild stress), SRWC 50% (moderate stress), and SRWC 35% (severe stress). Soil moisture was monitored using Spectrum® TDR150 (Spectrum Technologies, Inc., Aurora, IL, USA), with irrigation adjusted to maintain target SRWC levels. All non-water-related cultivation practices remained consistent. Each treatment included three biological replicates with ten trees per replicate.

2.2. Assessment of Creasing Incidence

Dynamic monitoring of creasing incidence at 191 DAF (initial symptom appearance) and continued at 15-day intervals. Satsuma mandarin creasing rate was calculated as follows:
Creasing rate (%) = (Number of creasing fruits/Total fruits assessed) × 100

2.3. Rind Microstructure Analysis

At 221 days after flowering (DAF), fruits exhibiting pronounced rind creasing under severe water stress (SRWC 35%) were sampled for comparative analysis of pericarp characteristics and anatomical microstructures. Equatorial rind segments (including flavedo and albedo) were excised, preserved in Formalin-Aceto-Alcohol (FAA) fixative, and processed for paraffin sections (8–10 μm thickness). The method for paraffin-embedding the rind and sectioning was performed according to Long [20].

2.4. Antioxidant Parameter Assay

Malondialdehyde (MDA), hydrogen peroxide (H2O2), and proline (Pro) contents, along with superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities of satsuma mandarin rind were quantified using commercial assay kits (Shanghai Jining Biotechnology Co., Ltd., Shanghai, China) according to the manufacturer’s protocols (https://www.shjning.com/category.php?id=82, accessed on 1 October 2025). The analyses were performed using Shimadzu UV-2600 UV-Vis spectrophotometer (Shimadzu Corporation, Kyoto, Japan). The same spectrophotometer was used for the subsequent determination of cell wall components and fruit quality.

2.5. Phytohormone Quantification

The content of zeatin riboside (ZR), indole-3-acetic acid (IAA), methyl jasmonate (MeJA), gibberellic acid (GA3), and abscisic acid (ABA) were analyzed in rind tissues using ELISA [21].

2.6. Cell Wall Metabolite Assay

Protopectin and soluble pectin contents in fruit rinds were quantified using commercial assay kits (Shanghai Jining Biotechnology Co., Ltd., China) following the manufacturer’s protocols (https://www.shjning.com/category.php?id=84, accessed on 1 October 2025).
Quantification of cellulose and hemicellulose in fruit rinds was performed according to Huang et al. [14], with modifications. Dried rind samples were ground into powder, and 0.1 g aliquots were transferred to 50 mL centrifuge tubes. Then, 25 mL of sodium dodecyl sulfate (SDS) solution was added, followed by incubation in a boiling water bath for 1 h and centrifugation at 10,000× g for 10 min. The supernatant was discarded, and 25 mL of 2 M HCl was added to the pellet. After incubation in a boiling water bath for 50 min, the samples were cooled and centrifuged at 10,000× g for 10 min. The supernatant was collected for hemicellulose quantification using the orcinol assay. The pellet was washed twice with acetone, dried, and transferred to a 25 mL beaker. Then, 2.5 mL of 72% H2SO4 was added, and the mixture was incubated at 35 °C for 1 h. The solution was diluted to 25 mL with distilled water and centrifuged at 10,000× g for 10 min; the supernatant was used for cellulose quantification via the anthrone method.

2.7. Mineral Element Assay

Satsuma mandarin fruit rind was dried in an oven, ground into powder, and the content of mineral elements in the rind was determined by atomic absorption method [22].

2.8. Fruit Quality Analysis

Fruit weight was determined as the ten fruits’ mean. Fruit length and diameter and rind thickness were measured using vernier calipers, with values representing means from five biological replicates. Soluble solids content (SSC) was measured in creasing and control fruits using a digital refractometer (PAL-1, Atago, Japan). Total sugars were quantified via the anthrone–sulfuric acid method, ascorbic acid (vitamin C) by 2,6-dichloroindophenol titration, and titratable acidity (TA) through NaOH titration [23].

2.9. Statistical Analysis

Data are given as means ± SD and were analyzed by two-way ANOVA (SPSS 23.0) with Duncan’s multiple range test or Student’s t-test. Figures were generated using GraphPad Prism 10.

3. Results

3.1. Soil Water Content and Creasing Incidence

Water stress significantly increased the incidence of rind creasing. Under severe water stress (SRWC 35%), creasing rates were significantly higher (p < 0.05) than those in the other three treatments at 191, 206, and 221 days after flowering (DAF), exhibiting a 28% increase compared to the 80% SRWC at 221 DAF. Although no statistically significant differences occurred among SRWC 50%, 65%, and 80% treatments at 191 and 206 DAF, the creasing incidence consistently rose with the decreasing soil moisture content. By 221 DAF, both SRWC 50% and 65% treatments showed significantly higher creasing rates than the sufficient irrigation treatment (SRWC 80%) (Figure 1A). The results of the correlation analysis showed that the creasing incidence was significantly negatively correlated with SRWC at 221 DAF, with a correlation coefficient of −0.942 and a p-value of 0.031. At 191 and 206 DAF, the p-values were greater than 0.05; however, the correlation coefficients were still below −0.8, suggesting a strong negative trend between soil drought and the satsuma mandarin creasing occurrence.

3.2. Morphological and Anatomical Alterations of the Rind

A comparative analysis of creasing and healthy rinds revealed distinct morphological differences. As shown in Figure 2A, creasing fruits exhibited dimpled surfaces resembling a pineapple rind, with inconspicuous oil glands in the flavedo and degraded albedo tissue displaying visible cracking (Figure 2B). A paraffin section analysis quantified the oil gland parameters: healthy fruits showed oil gland diameters of 422.6 μm and a distribution density of 3.38 glands/mm2, whereas creasing rinds demonstrated significantly reduced diameters (271.8 μm, 35.7% decrease) and an elevated density (8.44 glands/mm2, 149.7% increase) (Figure 2C,D). This oil gland proliferation resulted in diminished interglandular spaces and the mechanical compression of adjacent parenchyma cells (Figure 2E), potentially compromising the structural integrity of the rind.

3.3. Alterations in Antioxidant Enzyme Activities and ROS Levels

Analysis of reactive oxygen species (ROS) and antioxidant enzyme activities in rind tissues revealed distinct profiles between creasing and healthy fruits. While the malondialdehyde (MDA) content showed no significant difference (Figure 3A), hydrogen peroxide (H2O2) levels were 47.1% higher in the creasing rinds (p < 0.05) (Figure 3B). As H2O2 represents a key ROS component, this elevation indicates enhanced oxidative stress in the creasing fruit rinds. Concurrently, creasing rinds exhibited a significantly increased accumulation of a cytoplasmic osmolyte proline (Pro, Figure 3C), along with elevated activities of the antioxidant enzymes peroxidase (POD) (Figure 3D), catalase (CAT) (Figure 3E), and superoxide dismutase (SOD) (Figure 3F). These responses demonstrate that creasing fruit experience heightened oxidative stress, triggering the compensatory activation of cellular defense mechanisms against ROS accumulation.

3.4. Alterations in Phytohormone Levels

Th phytohormone content of creasing rinds revealed a significant reduction of 17.2% in indole-3-acetic acid (IAA) (Figure 4A), 7.8% in zeatin riboside (ZR) (Figure 4B), and 50.2% in methyl jasmonate (MeJA) (Figure 4D) compared to healthy fruits, whereas gibberellic acid (GA3) (Figure 4C) and abscisic acid (ABA) (Figure 4E) showed no significant differences. These results suggest that the depletion of growth-promoting hormones (IAA and ZR) may impair cellular activity and compromise cell wall biosynthesis. Concurrently, severely reduced MeJA—a key mediator of stress resilience—likely diminished the rind’s tolerance to environmental challenges, thereby contributing to creasing initiation.

3.5. Alterations in Cell Wall Composition

A comparative analysis of cell wall metabolites revealed significant compositional differences between the creasing and healthy fruit rinds. Creasing fruits rinds exhibited a reduction of 44.6% in cellulose (Figure 5A), 31.7% in hemicellulose (Figure 5B), and 33.1% in protopectin (Figure 5C), alongside a concomitant 36.3% increase in soluble pectin (Figure 5D). As cellulose, hemicellulose, and protopectin constitute key structural components of the cell wall, their depletion directly compromises the rind’s rigidity. The observed accumulation of soluble pectin—a primary degradation product of protopectin—provides direct evidence of enhanced protopectin breakdown in creasing rinds.

3.6. Alterations in Mineral Elements

Mineral element analysis (Table 1) indicated no significant differences in macronutrient content between the creasing and healthy rinds. However, micronutrients exhibited marked alterations: aluminum (Al), iron (Fe), sodium (Na), nickel (Ni), vanadium (V), and gallium (Ga) significantly accumulated, while zinc (Zn), barium (Ba), tin (Sn), and mercury (Hg) decreased. Critically, reduced Zn, a regulator of cell wall-associated proteins such as expansins [24], implies that there is a disrupted cell wall metabolism in creasing pathogenesis. Furthermore, rare earth elements (REEs) showed distinct profiles: yttrium (Y) and lanthanum (La) diminished significantly, whereas scandium (Sc) increased. Given the documented roles of REEs in photosynthesis, assimilate partitioning, and secondary metabolism [21], these findings reveal the significant contributions of REEs to creasing development.

3.7. Alterations in Fruit Quality

A comparative analysis of creasing and normal fruits revealed no significant differences in fruit weight, length, and diameter. However, rind thickness increased significantly in creasing fruits. Internal quality parameters—including soluble solids content (SSC), soluble sugars, and titratable acidity (TA)—showed no statistical variation. Notably, the ascorbic acid (vitamin C) content was 10.1% lower in creasing fruits (Figure 6). Vitamin C plays a critical role in plant antioxidants and free-radical scavenging; this reduction indicates a compromised oxidative stress tolerance in creasing fruit.

4. Discussion

The occurrence of rind creasing severely compromises the marketability of citrus fruits. Investigating its causative factors and elucidating the underlying physiological mechanisms are critical for developing effective control strategies. Given the susceptibility of the satsuma mandarin to creasing, this study examined the relationship between soil drought intensity and creasing incidence, while analyzing alterations in rind morphology, phytohormone profiles, antioxidant status, cell wall metabolites, and the mineral element distribution of creasing fruit. These integrated analyses clarify the physiological basis of this disorder.
Our results demonstrate a strong negative correlation between the soil water content and creasing incidence in satsuma mandarins, with a lower soil moisture triggering higher disorder rates (Figure 1). This aligns with prior reports identifying summer/autumn drought stress as a key inducer of creasing in ‘Valencia’ sweet oranges [25]. Significant variation under different irrigation systems in the satsuma mandarin [26] further confirms that drought is a pivotal trigger. Ensuring adequate water supply during fruit maturation is therefore essential for mitigating creasing in the ‘Miyagawa Wase’ satsuma mandarin.
Anatomically, creasing manifests through albedo cracking and subsequent flavedo collapse, producing a fruit surface resembling a pineapple rind [27]. In our study, ‘Miyagawa Wase’ satsuma mandarin fruits exhibited pronounced surface irregularities, albedo breakdown, a significantly reduced oil gland diameter, and higher gland distribution density in flavedo (Figure 2E). The rind paraffin sections revealed the mechanical compression of parenchyma cells by densely packed oil glands, disrupting cellular architecture. Li et al. similarly reported the irregular cell arrangement and oil gland proliferation in creasing ‘Shatangju’ mandarins [10], supporting our hypothesis that oil gland compression disrupts intercellular connectivity, thereby driving creasing development.
Furthermore, while MDA levels showed no significant difference, creasing fruit rinds accumulated 47.1% more H2O2 than healthy fruits. Concurrent increases in the Pro content and antioxidant enzymes (SOD, POD, and CAT) activity (Figure 3) indicated elevated stress responses in creasing fruit rinds. This oxidative signature likely originates from water deficit-induced ROS accumulation [28,29,30], triggering the compensatory upregulation of enzymatic and non-enzymatic antioxidants.
Phytohormones modulate both growth and stress adaptation. Drought typically suppresses auxin and cytokinin biosynthesis [31], consistent with our observations of reduced IAA and ZR in creasing fruit rinds (Figure 4A,B). Notably, foliar NAA (synthetic auxin) and zinc applications lower creasing incidence while elevating endogenous IAA [10]. Previous research reports that MeJA enhances drought tolerance in wheat, alfalfa, and ryegrass [32,33] and mitigates heat stress in rice [34]. MeJA diminished by 50.2% in our study (Figure 4D). Thus, depleted MeJA likely compromises rind resilience, synergizing with the IAA/ZR reduction to impair cell wall integrity.
Citrus creasing fundamentally correlates with cell wall destabilization. We observed significant decreases of 44.6% in cellulose, 31.7% in hemicellulose, and 33.1% in protopectin, alongside a 36.3% increase in the soluble pectin in creasing ‘Valencia’ [6] and ‘Hong Jiang’ oranges [12]. As protopectin degradation yields soluble pectin [13], our data confirm that creasing coincides with structural polysaccharide hydrolysis, weakening the pericarp strength in satsuma mandarins.
Mineral elements critically regulate cell wall synthesis/degradation. Although calcium (Ca) fortifies cell walls [35] and exogenous Ca sprays suppress creasing in sweet oranges [4,5,17], our study detected no significant Ca difference between healthy and creasing fruit rinds, consistent with Phiri’s [7] study results. Zn, which modulates the cell wall enzyme activity [36,37,38], showed lower concentrations in creasing fruits, aligning with reports that Zn supplementation reduces ‘Shatangju’ mandarin creasing [10]. Conflicting results exist regarding potassium (K), with some studies reporting an association between K and citrus creasing, while others, however, found no such association [7,17]; our data showed no macronutrient (P, K, Ca, and Mg) differences. However, creasing rinds accumulated more Al, Fe, Na, Ni, V, Ga, and Sc but less Zn, Ba, Sn, Hg, Y, and La. Critically, reduced Zn (a regulator of expansins) suggests a disrupted cell wall metabolism. The altered rare earth elements (REEs: Y, La, and Sc)—which influence photosynthesis, assimilate partitioning, and secondary metabolism [24,39]—further indicate their potential roles in creasing development. It should be noted that although hazardous metal elements, including Hg, As, Cd, and Pb, were detected in the rinds of both creasing and healthy fruits, their concentration did not exceed the maximum limits stipulated by food safety standards [40,41]. Therefore, the satsuma mandarins from our experimental site pose no dietary risk. Collectively, these findings demonstrate that creasing arises from multi-element interactions rather than a single mineral deficiency.

5. Conclusions

This study elucidates the factors and physiological mechanisms governing rind creasing in satsuma mandarins through the comprehensive analysis of soil moisture effects, creasing-induced morphological alterations, antioxidant dynamics, phytohormone profiles, cell wall metabolites, and mineral redistribution. Our results demonstrate that drought stress serves as a critical environmental inducer of creasing. And increased oil gland density in the flavedo compresses adjacent cells, disrupting cellular integrity. Concurrently, the degradation of cell wall components, including cellulose, hemicellulose, and protopectin, further compromises rind cells’ structural strength. These morphological changes coincide with elevated oxidative stress, significant reductions in phytohormones (IAA, ZR, and MeJA), and altered mineral element content, which contribute to the rind cells’ structural instability. Collectively, these physiological disruptions lead to rind creasing in the satsuma mandarin (Figure 7). These results offer theoretical insights that can guide the breeding of creasing-tolerant citrus cultivars and the design of targeted management strategies to mitigate this disorder.

Author Contributions

Conceptualization, Y.L.; methodology, W.H.; software, W.H.; validation, W.H., W.F., and D.L.; formal analysis, W.F.; investigation, W.F., Z.X.; resources, Y.L.; data curation, L.Y., J.S.; writing—original draft preparation, W.H.; writing—review and editing, L.K., Y.L.; visualization, W.H., J.X.; supervision, Y.L.; project administration, W.H.; funding acquisition, Y.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Science and Technology Department of Jiangxi Province of China (Grant number: 20223BBF61007 and 20224BAB205026) and supported by the National Natural Science Foundation of China (Grant number: 32460749).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Relationship between SRWC and the incidence of creasing. (A) Creasing incidence in satsuma mandarin under different SRWC at different stages. Different letters indicate significant differences (p < 0.05), (Duncan’s multiple range test). (B) Correlation analysis between creasing rate and SRWC at 191 DAF. (C) Correlation analysis between creasing rate and SRWC at 206 DAF. (D) Correlation analysis between creasing rate and SRWC at 221 DAF. r, Pearson correlation coefficient; R2, coefficient of determination.
Figure 1. Relationship between SRWC and the incidence of creasing. (A) Creasing incidence in satsuma mandarin under different SRWC at different stages. Different letters indicate significant differences (p < 0.05), (Duncan’s multiple range test). (B) Correlation analysis between creasing rate and SRWC at 191 DAF. (C) Correlation analysis between creasing rate and SRWC at 206 DAF. (D) Correlation analysis between creasing rate and SRWC at 221 DAF. r, Pearson correlation coefficient; R2, coefficient of determination.
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Figure 2. Morphological and anatomical alterations of the fruit rind. (A) Appearance of the fruit; (B) flavedo and albedo; (C) oil gland size; (D) oil gland distribution density; and (E) micrograph of a flavedo wax section. Black arrow marks the oil glands. CK, healthy fruit; CR, creasing fruit. Scale bars, 1.0 cm in (A), 0.5 cm in (B), and 150 µm in (E). ** p <0.01, (Student’s t-test).
Figure 2. Morphological and anatomical alterations of the fruit rind. (A) Appearance of the fruit; (B) flavedo and albedo; (C) oil gland size; (D) oil gland distribution density; and (E) micrograph of a flavedo wax section. Black arrow marks the oil glands. CK, healthy fruit; CR, creasing fruit. Scale bars, 1.0 cm in (A), 0.5 cm in (B), and 150 µm in (E). ** p <0.01, (Student’s t-test).
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Figure 3. Antioxidant enzyme activities and ROS content in normal and creasing fruit rinds. (A) MDA content in rind; (B) H2O2 content in rind; (C) Pro content in rind; (D) POD activity in rind; (E) CAT activity in rind; and (F) SOD activity in rind. CK, healthy fruit; CR, creasing fruit. * p < 0.05; ** p < 0.01; and *** p <0.001 (Student’s t-test).
Figure 3. Antioxidant enzyme activities and ROS content in normal and creasing fruit rinds. (A) MDA content in rind; (B) H2O2 content in rind; (C) Pro content in rind; (D) POD activity in rind; (E) CAT activity in rind; and (F) SOD activity in rind. CK, healthy fruit; CR, creasing fruit. * p < 0.05; ** p < 0.01; and *** p <0.001 (Student’s t-test).
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Figure 4. Phytohormone content in rind. (A) IAA content in rind; (B) ZR content in rind; (C) GA3 content in rind; (D) MeJA content in rind; and (E) ABA content in rind. CK, healthy fruit; CR, creasing fruit. * p <0.05; *** p <0.001 (Student’s t-test).
Figure 4. Phytohormone content in rind. (A) IAA content in rind; (B) ZR content in rind; (C) GA3 content in rind; (D) MeJA content in rind; and (E) ABA content in rind. CK, healthy fruit; CR, creasing fruit. * p <0.05; *** p <0.001 (Student’s t-test).
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Figure 5. Cell wall components in rinds. (A) Cellulose; (B) hemicellulose; (C) protopectin; and (D) soluble pectin; CK, healthy fruit; CR, creasing fruit. * p <0.05; ** p <0.01 (Student’s t-test).
Figure 5. Cell wall components in rinds. (A) Cellulose; (B) hemicellulose; (C) protopectin; and (D) soluble pectin; CK, healthy fruit; CR, creasing fruit. * p <0.05; ** p <0.01 (Student’s t-test).
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Figure 6. Fruit quality. (A) Fruit weight; (B) fruit diameter; (C) fruit length; (D) rind thickness; (E) soluble solids content; (F) soluble sugar; (G) titratable acidity; and (H) ascorbic acid. * p < 0.05 (Student’s t-test).
Figure 6. Fruit quality. (A) Fruit weight; (B) fruit diameter; (C) fruit length; (D) rind thickness; (E) soluble solids content; (F) soluble sugar; (G) titratable acidity; and (H) ascorbic acid. * p < 0.05 (Student’s t-test).
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Figure 7. Physiological model for rind creasing disorder in satsuma mandarin. The up arrow indicates an increase in the content or activity of the substance, the down arrow represents a decrease in the content or activity of the substance.
Figure 7. Physiological model for rind creasing disorder in satsuma mandarin. The up arrow indicates an increase in the content or activity of the substance, the down arrow represents a decrease in the content or activity of the substance.
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Table 1. Mineral element content in satsuma mandarin rind.
Table 1. Mineral element content in satsuma mandarin rind.
Mineral Element (Unit)Content
CK 1CR 1
MacronutrientsP (g·kg−1)0.70 ± 0.030.71 ± 0.03
K (g·kg−1)15.1 ± 1.7316.23 ± 1.6
Ca (g·kg−1)1.07 ± 0.121.03 ± 0.03
Mg (g·kg−1)0.84 ± 0.160.98 ± 0.02
MicronutrientsAl (mg·kg−1)33.84 ± 1.2545.37 ± 3.41 *
Fe (mg·kg−1)20.35 ± 1.3336.76 ± 2.41 **
Zn (mg·kg−1)15.98 ± 3.11 *8.62 ± 0.67
Na (mg·kg−1)19.35 ± 2.2227.92 ± 1.49 **
Mn (mg·kg−1)24.43 ± 1.9623.02 ± 2.62
Sr (mg·kg−1)12.29 ± 1.5410.72 ± 0.13
Ba (mg·kg−1)7.44 ± 0.51 **3.98 ± 0.2
Cu (mg·kg−1)2.04 ± 0.22.91 ± 0.87
Ti (mg·kg−1)0.92 ± 0.211.37 ± 0.45
Ni (mg·kg−1)0.44 ± 0.201.42 ± 0.38 *
V (μg·kg−1)41.28 ± 3.2376.38 ± 10.43 **
Se (μg·kg−1)54.29 ± 49.6367.74 ± 48.36
Ga (μg·kg−1)48.32 ± 8.79105.70 ± 24.81 *
Mo (μg·kg−1)0.085 ± 0.02254.05 ± 14.54
Co (μg·kg−1)56.22 ± 5.3769.47 ± 21.63
Sn (μg·kg−1)19.33 ± 0.43 **12.67 ± 0.61
Zr (μg·kg−1)9.10 ± 6.0113.97 ± 1.92
Be (μg·kg−1)2.92 ± 1.462.17 ± 0.70
Bi (μg·kg−1)1.73 ± 0.262.35 ± 0.47
Cr (mg·kg−1)1.80 ± 0.513.76 ± 1.94
As (μg·kg−1)42.71 ± 9.0838.33 ± 7.58
Pb (μg·kg−1)93.57 ± 11.65109.33 ± 21.16
Hg (μg·kg−1)6.54 ± 0.3 *5.29 ± 0.47
Cd (μg/kg)6.42 ± 4.014.35 ± 1.37
Rare earth elementsY (mg·kg−1)1.99 ± 0.26 *0.97 ± 0.33
Sc (μg·kg−1)65.71 ± 14.32181.55 ± 38.39 **
La (mg·kg−1)1.28 ± 0.20 **0.14 ± 0.03
1 CK, healthy fruit; CR, creasing fruit. * p < 0.05; ** p < 0.01 (Student’s t-test).
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Hu, W.; Fu, W.; Liu, D.; Xiong, Z.; Yang, L.; Kuang, L.; Song, J.; Xie, J.; Liu, Y. Physiological Mechanisms of Drought-Induced Creasing in Citrus unshiu Marc: Roles of Antioxidant Dysregulation, Hormonal Imbalance, Cell Wall Degradation, and Mineral Redistribution. Horticulturae 2025, 11, 1197. https://doi.org/10.3390/horticulturae11101197

AMA Style

Hu W, Fu W, Liu D, Xiong Z, Yang L, Kuang L, Song J, Xie J, Liu Y. Physiological Mechanisms of Drought-Induced Creasing in Citrus unshiu Marc: Roles of Antioxidant Dysregulation, Hormonal Imbalance, Cell Wall Degradation, and Mineral Redistribution. Horticulturae. 2025; 11(10):1197. https://doi.org/10.3390/horticulturae11101197

Chicago/Turabian Style

Hu, Wei, Woxing Fu, Dechun Liu, Zhonghua Xiong, Li Yang, Liuqing Kuang, Jie Song, Jingheng Xie, and Yong Liu. 2025. "Physiological Mechanisms of Drought-Induced Creasing in Citrus unshiu Marc: Roles of Antioxidant Dysregulation, Hormonal Imbalance, Cell Wall Degradation, and Mineral Redistribution" Horticulturae 11, no. 10: 1197. https://doi.org/10.3390/horticulturae11101197

APA Style

Hu, W., Fu, W., Liu, D., Xiong, Z., Yang, L., Kuang, L., Song, J., Xie, J., & Liu, Y. (2025). Physiological Mechanisms of Drought-Induced Creasing in Citrus unshiu Marc: Roles of Antioxidant Dysregulation, Hormonal Imbalance, Cell Wall Degradation, and Mineral Redistribution. Horticulturae, 11(10), 1197. https://doi.org/10.3390/horticulturae11101197

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