A view on the role of metabolites in enhanced stem reserves remobilization in wheat under drought during grain filling

Terminal drought is one of the major factors limiting the yield of wheat (Triticum aestivum L.). Remobilization of pre-stored carbohydrates from stem to grain during grain filling is one of the drought tolerance mechanisms. To investigate the enhanced stem reserves remobilization under drought condition, we compared metabolome pattern of two contrasting wheat landraces (NO.49 and NO.14) during days after anthesis (DAA) under drought stress. Wheat genotypes were cultivated in a greenhouse and drought stress initiated just after anthesis and peduncle, penultimate and lower internodes samples were collected from well-watered and drought-stressed plants at 0, 10, 20 and 30 DAA. The peduncle of NO.49 showed remarkably higher stem reserves remobilization efficiency compared with NO.14 during this period. The higher content of fructan in peduncle of NO.49 genotype under drought stress suggesting a higher oxidative stress defense response and a faster fructan remobilization supports grain filling under stress. A positive correlation observed between the fructan and sucrose:sucrose fructosyltransferase (SST) activity (r2=0.77) in No.49, whereas this was not the case in NO.14 genotype. A higher Invertase (INV) activity in NO.49 genotype under drought stress compared with control during 20 DAA revealed an increase in sucrose degradation during fructan remobilization. The decrease in arginine and increase in proline content in NO.49 under drought stress only during 10 DAA could be considered as the index of senescence initiation. Increase accumulation of arginine and ACC amino acids in NO.49 peduncle in after anthesis period, suggesting enhancement of senescence during grain filling. Our results indicate that carbon remobilization in NO.49 increases from the stem to the grains by a good coordination between enhancing senescence and oxidative stress defense to protect stem cells from premature cell death.