Lack of functional interrelationship between β-amylase photoregulation and chloroplast development in mustard (sinapsis alba l.) cotyledons

Abstract

In the cotyledons of mustard seedlings light mediates an increase in β-amylase [EC 3.2.1.2] activity via agency of phytochrome. In order to understand the functional significance of above photoresponse, the relationship between light induced β-amylase increase, chloroplast development and starch content of cotyledon was investigated. The application of SAN 9789 a chlorosis inducing inhibitor to mustard seedlings, though destroyed chloroplast, had no effect on light mediated increase in β-amylase indicating the lack of functional interrelationship between chloroplast development and β-amylase increase. The subcellular localization studies revealed that β-amylase is a cytosolic enzyme. Additionally, the increase in the level of β-amylase had no relationship with in vivo starch level, which was present only in trace amounts. The noncorrelation of the photoregulated β-amylase increase with the starch content and its extra-chloroplastic localization indicates that β-amylase does not participate in the mobilization of plastidic starch in mustard cotyledon. © 1990. The Japanese Society of Plant Physiologists (JSPP).