Lipid-sugar conversion regulates early white clover (Trifolium repens) seedling establishment under cadmium stress

In addition to amylolysis, the maintenance of higher lipid-sugar conversion for energy supply contributes to better adaptation to Cd stress during early white clover seedling establishment. Soil cadmium (Cd) contamination threatens the survival of plants and also poses a major threat to the food chain. White clover (Trifolium repens) is an excellent leguminous plant for remediation of Cd-contaminated lands and enhancement of biodiversity in grassland ecosystems. However, the potential mechanism of Cd tolerance is not well elucidated during early white clover seedling establishment. Integrative biochemical, molecular, and lipidomic approaches were used to investigate common and differential responses to Cd stress between two white clover cultivars (Cd-tolerant Barbzan and Cd-sensitive Haifa) and further reveal potential mechanism of Cd tolerance related to amylolysis, lipid remodeling, and lipid-sugar conversion during early seedling establishment. The results showed that Cd stress significantly reduced amylolysis and sugar metabolism by restraining amylases and sucrose activities, which significantly limited early white clover seedling establishment. However, Cd-tolerant Barbzan exhibited better seedling growth, lower lipid peroxidation, and better cell membrane stability than Cd-sensitive Haifa in response to Cd stress. Although no significant difference in the amylolysis was detected between two cultivars, Barbzan accumulated more glucose and sucrose compared with Haifa under Cd stress. Analyses of lipidomics and gene expression demonstrated that Barbzan exhibited significantly lower lipid content, but higher transcript levels of multiple genes (TrSDP1, TrGPDH, TrGPDHC1, TrACX1, TrACX2, and TrPCK1) involved in the lipid-sugar conversion for the gluconeogenesis during early seedling establishment under Cd stress. In addition, Barbzan had significantly lower unsaturation level of sphingolipids and higher content of phosphatidylinositol triphosphate (PIP3) than Haifa in response to Cd stress. These findings indicate that the maintenance of higher lipid-sugar conversion for energy supply contributes to better adaptation to Cd stress during early seedling establishment.