ABSTRACT
Introduction: Salt stress is a major abiotic stress that affects crop growth and productivity. Choline Chloride (CC) has been shown to enhance salt tolerance in various crops, but the underlying molecular mechanisms in rice remain unclear. Methods: To investigate the regulatory mechanism of CC-mediated salt tolerance in rice, we conducted morpho-physiological, metabolomic, and transcriptomic analyses on two rice varieties (WSY, salt-tolerant, and HHZ, salt-sensitive) treated with 500 mg·L-1 CC under 0.3% NaCl stress. Results: Our results showed that foliar application of CC improved morpho-physiological parameters such as root traits, seedling height, seedling strength index, seedling fullness, leaf area, photosynthetic parameters, photosynthetic pigments, starch, and fructose content under salt stress, while decreasing soluble sugar, sucrose, and sucrose phosphate synthase levels. Transcriptomic analysis revealed that CC regulation combined with salt treatment induced changes in the expression of genes related to starch and sucrose metabolism, the citric acid cycle, carbon sequestration in photosynthetic organs, carbon metabolism, and photosynthetic antenna proteins in both rice varieties. Metabolomic analysis further supported these findings, indicating that photosynthesis, carbon metabolism, and carbon fixation pathways were crucial in CC-mediated salt tolerance. Discussion: The combined transcriptomic and metabolomic data suggest that CC treatment enhances rice salt tolerance by activating distinct transcriptional cascades and phytohormone signaling, along with multiple antioxidants and unique metabolic pathways. These findings provide a basis for further understanding the mechanisms of metabolite synthesis and gene regulation induced by CC in rice in response to salt stress, and may inform strategies for improving crop resilience to salt stress.
ABSTRACT
BACKGROUND: Salinity stress is an environmental constraint that normally develops concurrently under field conditions, resulting in drastic limitation of rice plant growth and grain productivity. The objective of this study was to explore the alleviating effects of NaCl pre-treatment on rice seedlings as well as the salt tolerance mechanisms by evaluating morph-physiological traits. RESULTS: Variety Huanghuazhan, either soaked in distilled water or 25 mg/L Prohexadione calcium (Pro-Ca), were first hardened with varying concentrations of NaCl solutions (0 and 50 mM NaCl), and then subjected to varying degrees of salt stress (0 and 100 mM NaCl), indicated by S0, S1, S2 and S3, respectively. Growth analysis suggested that NaCl-pretreatment improved the root/shoot ratio in water-soaked rice plant at DAP 0. Data related to the reaction center density, photosynthetic electron transport efficiency, trapping efficiency were compared before (CK) using performance Index (PIabs). Compared to S2 (Pro-Ca-S2) treatment, PIabs did not show any difference with plants pre-treated with NaCl (S3 or Pro-Ca-S3). Rather than PIabs, significant difference was found in photosynthetic electron transport efficiency (ΨEo). The ΨEo value in Pro-S2 was significantly lowered as compared to Pro-S3 treatment at DAP 7, and the decrease rate was about 6.5%. Correlation analysis indicated leaf PIabs was weak correlated with plant biomass while the quantum yield for reduction of the PSI end electron acceptors, trapped energy flux per reaction center and PSII antenna size displayed strong positive correlation with biomass. Additional analysis revealed that 100 mM NaCl significantly reduced leaf linear electron flux under low-light conditions, regardless of whether seedlings had been pre-treated with 50 mM NaCl or not. CONCLUSIONS: NaCl-induced salt tolerance was related to the robust photosynthetic machinery.