Metabolomic characterization of alkali stress responses in rice

Soil alkalinity due to the accumulation of alkaline salts greatly impairs crop production. Despite advancements in crop stress response studies through metabolomic analyses, limited progress has been made in understanding cultivar differences in alkali tolerance due to the scarcity of suitable genetic material. This study aimed to characterize the metabolic responses to alkali stress in two rice cultivars, Kasalath (alkali-sensitive) and Gharib (alkali-tolerant), which were screened in an alkali soil field. A metabolomic analysis of the responses of hydroponically grown seedlings of both cultivars to alkaline and neutral salt stress was performed. Under alkali stress, the tolerant cultivar Gharib showed a significant accumulation of metabolites from the TCA organic acid and arginine synthesis pathways. This accumulation is consistent with observations in alkaliphilic wild grasses and may account for the superior alkali tolerance of Gharib. Although amino acids and nitrogen-containing metabolites, such as asparagine and allantoin, also accumulated under alkali stress, their accumulation was not specific to alkali stress, as previously reported. They accumulated similarly in both Kasalath and Gharib, suggesting that while these metabolites may alleviate alkali stress, they are unlikely to be responsible for cultivar differences in rice alkali tolerance.