Metabolic responses of alfalfa (Medicago Sativa L.) leaves to low and high temperature induced stresses

Abstract

To explore adaptation mechanism of alfalfa to cold and heat stresses, status of sucrose metabolism and relative water content (RWC) in leaves under low and high temperature treatments were studied. Seedlings (35 day old) were transferred to chambers for treatments. First group was subjected to 5°C as low temperature (LT) stress, second group at 33°C as high temperature (HT) stress and third group at 25°C as the control (CK). Results indicated that, both stresses led to an increase in degree and duration of genes expression and corresponding enzymes activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS), but LT showed a more significant effect. As a result, lower starch content and higher contents of soluble reducing sugar, fructose and sucrose were observed under LT stress. Moreover, LT stress lowered malondialdehyde (MDA) content and electrolyte leakage in leaves, thus achieving a higher RWC. It was suggested that, relatively higher RWC in leaves by LT stress resulted from lowered water potential, and transpiration can explain the reason that alfalfa plants are cold-tolerant but heat-sensitive.

Key words: Alfalfa, temperature stress, sucrose, sucrose phosphate synthase (SPS), relative water content.