Silicon mediated redox homeostasis in the root-apex transition zone of rice plays a key role in aluminum tolerance

Organosilicon enhances rice root suberization and antioxidant gene expression under cadmium/arsenic stress

Organosilicon exhibits unique physicochemical and biological properties with wide applicability across diverse fields, including agriculture and industry. Previous research has verified the effectiveness of organosilicon-modified fertilizers in inhibiting the uptake of cadmium (Cd) and arsenic (As) by plants. However, further investigations are necessary to elucidate the underlying mechanisms. In this study, we explored the potential of organosilicon to mitigate the toxic effects of Cd/As and lessen their uptake and accumulation during rice seed germination. Our results showed that under Cd/As stress, organosilicon treatments significantly increased suberin biosynthesis in rice roots. This was manifested as an increased level of root suberization and an enhanced apoplast barrier, as verified by observations made through fluorol yellow (FY) staining and transmission electron microscopy (TEM). Consequently, the uptake and translocation of Cd and As in rice seedlings were significantly reduced by 48.66 % and 72.19 % in shoots, and 43.23 % and 68.93 % in roots, respectively. Moreover, the application of organosilicon enhanced the activities of antioxidant enzymes in rice, This lead to an accelerated glutathione-oxidized glutathione (GSH-GSSG) cycle, up-regulated expression of the rice glutathione peroxidase gene (OsGPX), and increased GPX activity. These modifications effectively scavenged reactive oxygen species (ROS) generated by Cd/As stress and alleviated oxidative damage in rice. Overall, our study has unraveled the physiological and molecular mechanisms underlying the role of organosilicon in alleviating Cd/As toxicity in rice and has also provided new insights for the application of suberin in reducing heavy metal toxicity in plants.

Silicon alleviates aluminum-induced inhibition of photosynthetic and growth attributes in rice by modulating competitive pathways between ethylene and polyamines and activating antioxidant defense

Silicon (Si) has been reported to mitigate aluminium (Al3+) toxicity in rice; however, the mechanism underlying this beneficial effect has not been fully elucidated. In this study, Si addition increased the total level of both free and conjugated putrescine (Put) content in rice leaves by 89.3 % through up-regulation of the key synthesis genes in both of arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) pathways under Al stress. The production of total Put increased by 10.3 % under Si treatment but decreased by 11.7 % under Al treatment compared to the control. Similarly, Si increased total spermidine (Spd) and spermine (Spm) levels by 154.9 % and 83.5 %, respectively, through up-regulation of S-adenosyl-Met-decarboxylase genes (SAMDC1 and SAMDC2), spermidine synthase genes (SPDS1 and SPDS2), and spermine synthase gene (SPMS) under Al stress. Compared with Al treatment alone, Si significantly increased the levels of free, conjugated and total polyamines (PAs) in leaves under Al stress by 106.1 %, 86.6 % and 99.3 %, respectively. The increase of PAs induced by Si maintained redox balance and improved photosynthetic capacity, ultimately increasing rice growth by 28.6 % under Al stress. Conversely, Si reduced Al-induced increase in 1-aminocyclopropane-1-carboxylate (ACC) content and ethylene production by 23.9 % and 43.8 %, respectively, through down-regulation of ACC synthase genes (ACS1 and ACS2) and ACC oxidase ACO genes (ACO1 and ACO4). In addition, Si mitigated the Al-induced oxidative damage by reducing the accumulation of reactive oxygen species (ROS) through activation of enzymatic (superoxide dismutase and catalase) and non-enzymatic (ascorbate-glutathione cycle) antioxidant defence systems. We therefore propose that Si attenuates Al-induced damage on rice photosynthetic apparatus by modulating competitive interactions between ethylene and PA biosynthesis and activating ROS scavenging capacity.

Physiological basis of nano-silica deposition-related improvement in aluminum tolerance in pea (Pisum sativum)

Aluminum(Al) toxicity is a major constraint affecting crop growth in acidic soils across the globe. Excessive Al levels in such soils not only negatively affect crop growth but also have significant implications for human health. This study aimed to explore the feasibility of increasing tolerance to Al stress by creating biomineralization structures in plant roots by nano-silica, and to explore the physiological basis silicon-mediated alleviation of Al toxicity in plants. The polyethylenimine was used to induce nano-silica to form biomineralization structures on the surface of root tip and root border cells in pea (Pisum sativum) plants. The results showed that under Al stress conditions, the deposition of nano-silica on the cell wall of pea root border cells induced by polyethyleneimine effectively increased cell viability and reduced reactive oxygen species(ROS) production by 44%, thus slowing down the programmed cell death. Such deposition also resulted in more Al ions(Al3+) absorbed by the surface of the root tip, thus preventing Al3+ from entering the root tip and alleviating the toxic effects of Al on cell metabolism. It is concluded that polyethylenimine- induced nano-silica deposition on the cell wall endows pea root cells with Al tolerance, thus enhancing crop growth and reducing toxic Al load, contributing to food safety and human health.

Melatonin-priming ameliorates aluminum accumulation and toxicity in rice through enhancing aluminum exclusion and maintaining redox homeostasis

Seed priming can effectively enhance the plant's ability to withstand stress during subsequent growth and development; however, the role of melatonin-priming in attenuating aluminum (Al) toxicity remain unknown. In this study, 10, 50 and 100 μM melatonin were selected for rice seed priming to investigate the protective effects and potential mechanisms of melatonin against Al toxicity. Al stress inhibited seed germination by induction of abscisic acid (ABA) accumulation and reduction of α-amylase activity. However, melatonin-priming substantially rescued the Al-induced poor germination of seeds, as evidenced by less ABA content and higher α-amylase activity. Compared to no priming under Al stress, melatonin-priming significantly increased root elongation and plant fresh weight of rice seedlings by 135.1% and 39.4%, respectively. Melatonin-priming scavenged Al-induced superoxide anion (O2·-) and hydrogen peroxide (H2O2) bursts by activating the antioxidant enzymes (superoxide dismutase and catalase) and antioxidants (ascorbate and glutathione) in root tips, thereby reducing malondialdehyde (MDA) and callose levels and ultimately mitigating oxidative damage. Furthermore, melatonin-priming enhanced Al resistance by inhibiting Al uptake into the symplast through increased citric acid secretion. The decrease of Al deposition in the cell wall was attributed to melatonin-stimulated reduction of cell wall pectin and hemicellulose contents under Al stress. Collectively, these findings reveal a positive role of melatonin-priming in alleviating Al toxicity in plants.

Glutathione mitigates aluminum toxicity in root-apex transition zone of rice through reducing aluminum absorption and maintaining redox balance

Aluminium (Al) toxicity is recognized as a major constraint on crop growth and production in acidic soils, and the transition zone (TZ) of plant root apex emerges as the major perception site of Al toxicity. Glutathione (GSH) is reported to be involved in plant responses to various abiotic stresses, but its role and mechanism under Al stress remain unknown. Here, we found that GSH significantly mitigated Al toxicity on rice as revealed by the promotion of root elongation, reduction of oxidative stress and Al absorption. GSH application scavenged Al-induced H2O2 burst by activating the ascorbate (AsA)-GSH cycle and proline synthesis in root-apex TZ, thereby alleviating oxidative stress. GSH effectively reduced Al-induced pectin increment and inhibits the H2O2-induced pectin methylesterase (PME) activity and demethylesterification degree in root-apex TZ, leading to a reduction in Al binding sites and subsequently Al deposition in cell walls, thereby attenuating the inhibitory effect of Al toxicity on cell elongation. In addition, GSH-derived phytochelatins (PCs) promoted the vacuolar Al sequestration in root-apex TZ, which alleviated Al toxicity to the cytoplasm. Taken together, our results indicate a mechanism underlying how GSH alleviates Al toxicity through influencing redox state and Al absorption in rice root-apex TZ.

Silicon efficacy for the remediation of metal contaminated soil

In the course of past two decade anthropogenic activities have reinforced, begetting soil and water defilement. A plethora of heavy metals alters and limits plant growth and yield, with opposing effect on agricultural productivity. Silicon often perceived as plant alimentary 'nonentity'. A suite of determinants associated with silicon have been lately discerned, concerning plant physiology, chemistry, gene regulation/expression and interaction with different organisms. Exogenous supplementation of silicon renders resistance against heavy-metal stress. Predominantly, plants having significant amount of silicon in root and shoot thus are barely prone to pest onset and manifest greater endurance against abiotic stresses including heavy-metal toxicity. Silicon-mediated stress management involves abatement of metal ions within soil, co-precipitation of metal ions, gene modulation associated with metal transport, chelation, activation of antioxidants (enzymatic and non-enzymatic), metal ion compartmentation and structural metamorphosis in plants. Silicon supplementation also stimulates expression of stress-resistant genes under heavy-metal toxicity to provide plant tolerance under stress conditions. Ergo, to boost metal tolerance within crops, immanent genetic potential for silicon assimilation should be enhanced. Current study, addresses the potential role and mechanistic interpretation of silicon induced mitigation of heavy-metal stress in plants.

Root-zone regulation and longitudinal translocation cause intervarietal differences for phthalates accumulation in vegetables

Selecting and cultivating low-accumulating crop varieties (LACVs) is the most effective strategy for the safe utilization of di-(2-ethylhexyl) phthalate (DEHP)-contaminated soils, promoting cleaner agricultural production. However, the adsorption-absorption-translocation mechanisms of DEHP along the root-shoot axis remains a formidable challenge to be solved, especially for the research and application of LACV, which are rarely reported. Here, systematic analyses of the root surface ad/desorption, root apexes longitudinal allocation, uptake and translocation pathway of DEHP in LACV were investigated compared with those in a high-accumulating crop variety (HACV) in terms of the root-shoot axis. Results indicated that DEHP adsorption was enhanced in HACV by root properties, elemental composition and functional groups, but the desorption of DEHP was greater in LACV than HACV. The migration of DEHP across the root surface was controlled by the longitudinal partitioning process mediated by root tips, where more DEHP accumulated in the root cap and meristem of LACV due to greater cell proliferation. Furthermore, the longitudinal translocation of DEHP in LACV was reduced, as evidenced by an increased proportion of DEHP in the root apoplast. The symplastic uptake and xylem translocation of DEHP were suppressed more effectively in LACV than HACV, because DEHP translocation in LACV required more energy, binding sites and transpiration. These results revealed the multifaceted regulation of DEHP accumulation in different choysum (Brassica parachinensis L.) varieties and quantified the pivotal regulatory processes integral to LACV formation.

OsAlR3 regulates aluminum tolerance through promoting the secretion of organic acids and the expression of antioxidant genes in rice

In acidic soils, aluminum (Al) toxicity inhibits the growth and development of plant roots and affects nutrient and water absorption, leading to reduced yield and quality. Therefore, it is crucial to investigate and identify candidate genes for Al tolerance and elucidate their physiological and molecular mechanisms under Al stress. In this study, we identified a new gene OsAlR3 regulating Al tolerance, and analyzed its mechanism from physiological, transcriptional and metabolic levels. Compared with the WT, malondialdehyde (MDA) and hydrogen peroxide (H2O2) content were significantly increased, superoxide dismutase (SOD) activity and citric acid (CA) content were significantly decreased in the osalr3 mutant lines when exposed to Al stress. Under Al stress, the osalr3 exhibited decreased expression of antioxidant-related genes and lower organic acid content compared with WT. Integrated transcriptome and metabolome analysis showed the phenylpropanoid biosynthetic pathway plays an important role in OsAlR3-mediated Al tolerance. Exogenous CA and oxalic acid (OA) could increase total root length and enhance the antioxidant capacity in the mutant lines under Al stress. Conclusively, we found a new gene OsAlR3 that positively regulates Al tolerance by promoting the chelation of Al ions through the secretion of organic acids, and increasing the expression of antioxidant genes.

Silicon attenuates aluminum toxicity in sugarcane plants by modifying growth, roots morphoanatomy, photosynthetic pigments, and gas exchange parameters

Aluminum (Al) inhibits growth and limits plant productivity in acidic soils. An important strategy to increase Al tolerance is the use of silicon (Si) nutrition. Thus, the aim of this study was to evaluate the interactive role of Si in increasing the growth, physiological and morphoanatomy responses of sugarcane plants under Al toxicity. A 4 × 2 factorial scheme in a completely randomized design was used to study the impact of Si (2 mM) on attenuating Al toxicity (0, 10, 15 and 20 mg L-1, as Al2(SO4)3·18H2O) in sugarcane seedlings. After 45 days, Al toxicity affected sugarcane growth by increasing Al uptake and accumulation, modifying root growth, thickness, and morphoanatomy, and decreasing pigment content, gas exchange parameters, and the number of adaxial and abaxial stomata. However, Si attenuated Al toxicity in the sugarcane seedlings by limiting Al uptake and transport to the shoots, causing positive changes in root morphoanatomy, higher pigment content, improving gas exchange parameters, thereby increased growth. Furthermore, cultivar 'CTC9003' showed beneficial impacts from Si supplementation than 'CTC9002', especially under Al toxicity. The findings of this study suggest that Si plays a notable role in improving anatomical and physiological aspects, particularly the growth of sugarcane seedlings under Al toxicity.

The effects of different iron and phosphorus treatments on the formation and morphology of iron plaque in rice roots (Oryza sativa L)

Introduction

Rice (Oryza sativa L.) is a pivotal cereal crop worldwide. It relies heavily on the presence of iron plaque on its root surfaces for optimal growth and enhanced stress resistance across diverse environmental conditions.

Method

To study the crystallographic aspects of iron plaque formation on rice roots, the concentrations of Fe2+ and PO4 3- were controlled in this study. The effects of these treatments were assessed through comprehensive analyzes encompassing root growth status, root surface iron concentration, root vitality, enzyme activities, and microstructural characteristics using advanced techniques such as root analysis, scanning electron microscopy (SEM), and ultrathin section transmission electron microscopy (TEM).

Results

The results demonstrated that an increase in the Fe2+ concentration or a decrease in the PO4 3- concentration in the nutrient solution led to improvements in various root growth indicators. There was an elevation in the DCB (dithionite-citrate-bicarbonate) iron content within the roots, enhanced root vitality, and a significant increase in the activities of the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) enzymes. Moreover, as the Fe2+ concentration increased, amorphous iron oxide minerals on the root surface were gradually transformed into ferrihydrite particles with sizes of approximately 200 nm and goethite particles with sizes of approximately 5 μm. This study showed that an increase in the Fe2+ concentration and a decrease in the PO4 3- concentration led to the formation of substantial iron plaque on the root surfaces. It is noteworthy that there was a distinct gap ranging from 0.5 to 3 μm between the iron plaque formed through PO4 3- treatment and the cellular layer of the root surface.

Discussion

This study elucidated the impacts of Fe2+ and PO4 3- treatments on the formation, structure, and morphology of the iron plaque while discerning variations in the spatial proximity between the iron plaque and root surface under different treatment conditions.

Physiological and Transcriptomic Analysis Reveals That Melatonin Alleviates Aluminum Toxicity in Alfalfa (Medicago sativa L.)

Aluminum (Al) toxicity is the most common factor limiting the growth of alfalfa in acidic soil conditions. Melatonin (MT), a significant pleiotropic molecule present in both plants and animals, has shown promise in mitigating Al toxicity in various plant species. This study aims to elucidate the underlying mechanism by which melatonin alleviates Al toxicity in alfalfa through a combined physiological and transcriptomic analysis. The results reveal that the addition of 5 μM melatonin significantly increased alfalfa root length by 48% and fresh weight by 45.4% compared to aluminum treatment alone. Moreover, the 5 μM melatonin application partially restored the enlarged and irregular cell shape induced by aluminum treatment, resulting in a relatively compact arrangement of alfalfa root cells. Moreover, MT application reduces Al accumulation in alfalfa roots and shoots by 28.6% and 27.6%, respectively. Additionally, MT plays a crucial role in scavenging Al-induced excess H2O2 by enhancing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), consequently reducing malondialdehyde (MDA) levels. More interestingly, the RNA-seq results reveal that MT application significantly upregulates the expression of xyloglucan endotransglucosylase/hydrolase (XTH) and carbon metabolism-related genes, including those involved in the glycolysis process, as well as sucrose and starch metabolism, suggesting that MT application may mitigate Al toxicity by facilitating the binding of Al to the cell walls, thereby reducing intracellular Al accumulation, and improving respiration and the content of sucrose and trehalose. Taken together, our study demonstrates that MT alleviates Al toxicity in alfalfa by reducing Al accumulation and restoring redox homeostasis. These RNA-seq results suggest that the alleviation of Al toxicity by MT may occur through its influence on cell wall composition and carbon metabolism. This research advances our understanding of the mechanisms underlying MT's effectiveness in mitigating Al toxicity, providing a clear direction for our future investigations into the underlying mechanisms by which MT alleviates Al toxicity in alfalfa.