Modulation of Sucrose and Starch Metabolism by Salicylic Acid Induces Thermotolerance in Spring Maize

Abstract

Two inbred lines of spring maize (Zea mays L.), CML 32 (stress tolerant) and LM 11 (stress susceptible) were taken to study the effect of salicylic acid (SA) on their carbohydrate status, under heat stress. Heat stress increased the content of total soluble sugars and sucrose in the shoots and residual mass of CML 32 seedlings. On the other hand, the shoots and roots of LM 11 seedlings showed reduced sucrose content. Application of SA increased the contents of total soluble sugars and sucrose in the roots and shoots of both the inbred lines. Heat stress reduced the activities of acid and neutral invertases in the shoots of CML 32 seedings that corresponded with their increased sucrose content. Foliar spray of SA increased acid invertase but decreased neutral invertase activities in shoots of both the inbred lines that might help in maintaining sucrose levels and energy needs for better seedling growth under stress conditions. Heat stress induced CML 32 seedlings to exhibit stress tolerance by increasing amylase activity in their residual masses that led to their reduced starch content. SA application reduced the amylolytic activity of the residual mass of CML 32 seedlings that corresponded with their higher starch content. SA application led to increased sucrose synthase (synthesis) and sucrose phosphate synthase activities in the roots of both the inbred lines and the shoots of CML 32 seedlings. It also decreased sucrose synthase (cleavage) activity in CML 32 roots and LM 11 shoots, under heat stress leading to optimization of their sucrose levels.