Soil alkalization is an important environmental factor limiting crop production. Despite the importance of root secretion in the response of plants to alkali stress, the regulatory mechanism is unclear. In this study, we applied a widely targeted metabolomics approach using a local MS/MS data library constructed with authentic standards to identify and quantify root exudates of wheat under salt and alkali stresses. The regulatory mechanism of root secretion in alkali-stressed wheat plants was analyzed by determining transcriptional and metabolic responses. Our primary focus was alkali stress-induced secreted metabolites (AISMs) that showed a higher secretion rate in alkali-stressed plants than in control and salt-stressed plants. This secretion was mainly induced by high-pH stress. We discovered 55 AISMs containing –COOH groups, including 23 fatty acids, 4 amino acids, 1 amino acid derivative, 7 dipeptides, 5 organic acids, 9 phenolic acids, and 6 others. In the roots, we also discovered 29 metabolites with higher levels under alkali stress than under control and salt stress conditions, including 2 fatty acids, 3 amino acid derivatives, 1 dipeptide, 2 organic acids, and 11 phenolic acids. These alkali stress-induced accumulated carboxylic acids may support continuous root secretion during the response of wheat plants to alkali stress. In the roots, RNAseq analysis indicated that 5 6-phosphofructokinase (glycolysis rate-limiting enzyme) genes, 16 key fatty acid synthesis genes, and 122 phenolic acid synthesis genes have higher expression levels under alkali stress than under control and salt stress conditions. We propose that the secretion of multiple types of metabolites with a –COOH group is an important pH regulation strategy for alkali-stressed wheat plants. Enhanced glycolysis, fatty acid synthesis, and phenolic acid synthesis will provide more energy and substrates for root secretion during the response of wheat to alkali stress.

Saline-sodic stress induces iron deficiency in rice, reduces leaf photosynthetic performance, and inhibits yield enhancement. In this study, we investigated the effects of exogenous Fe on the photosynthetic performance and transcriptomics of two different tolerant rice cultivars CB9 (Changbai9: saline tolerant cultivar) and TH899 (Tonghe899: saline sensitive cultivar) with 4-week-old Fe-deficient rice seedlings under saline stress, Fe deficiency stress, and both co-stresses. The results showed that under saline and alkaline stress, spraying exogenous iron favored the growth of the two cultivars of rice, with a 32.68% and 39.82 increase in fresh weight, a 2.20-fold and 2.16-fold increase in pigment, respectively, and an 80.28% and 100.00% increase in net photosynthetic rate, respectively, as compared with the iron-deficiency treatment. Transcriptome analysis showed that we found a higher number of differentially expressed genes (7785 differentially expressed genes) in response to exogenous Fe spraying in the soda-salt sensitive variety TH899. The differentially expressed genes that are common to the two cultivars are primarily enriched in metabolic pathways, including plant hormone signal transduction (map04075) and phenylpropanoid biosynthesis (map00940). Specifically, among these genes, 14 are differentially expressed in the carotenoid biosynthetic metabolic pathway. The differentially expressed genes specific to the salinity-tolerant variety CB9 were mainly enriched in the metabolic pathways of glyoxylate and dicarboxylic acid methyl metabolism (map00630), and carbon fixation in photosynthetic organisms (map00710), among which 20 genes were significantly expressed in the pathway for carbon fixation in photosynthetic organisms (map00710). The research results offer specific theoretical support for enhancing the salt tolerance of rice.