Impact of Heat-Shock Treatment on Yellowing of Pak Choy Leaves

摘要

The physiological mechanism of maintaining the green colour of pak choy leaves (Brassies rapa var chinensis) with heat-shock treatment was studied, Chlorophyll in the outer leaves of pak choy degraded rapidly during storage at ambient temperature (20±2°C), a slight yellow appeared, Heat-shock treatment (46-50°C) had a mild effect on maintaining the green colour of outer leaves. Normal chlorophyll degradation was associated with a binding of chlorophyll with chlorophyll-binding-protein preceding chlorophyll breakdown. Heat-shock treatment was found to reduce the binding-capacity between chlorophyll-binding-protein and chlorophyll. In the chlorophyll degradation pathway, pheide dioxygenase was synthesized during leaf senescence which was consideredto be a key enzyme in chlorophyll degradation. Activity of this enzyme was reduced following heat-shock treatment, which might explain the observed reduction in chlorophyll breakdown. Two groups of heat-shock proteins were detected in treated leaves, the first group containing proteins from 54 KDa to 74 Kda, and the second group contained proteins from 15 KDa to 29 KDa Heat-shock treatment was also found to retard the decline of glucose and fructose (the main energy substrates) of outer leaves.