Amylases in Pea Tissues with Reduced Chloroplast Density and/or Function

Abstract

Pea (Pisum sativum L.) tissues with reduced chloroplast density (e.g. petals and stems) or function (i.e. senescent leaves and leaves darkened for prolonged periods) were surveyed to determine whether tissues with genetically or environmentally reduced chloroplast density and/or function also have significantly different amylolytic enzyme activities and/or isoform patterns than leaf tissues with totally competent chloroplasts. Native PAGE followed by electrophoretically blotting through a starch or beta-limit dextrin containing gel and KI/I(2) staining revealed that the primary amylases in leaves, stems, petals, and roots were the primarily vacuolar beta-amylase (EC 3.2.1.2) and the primarily apoplastic alpha-amylase (EC 3.2.1.1). Among tissues of light grown pea plants, petals contained the highest levels of total amylolytic (primarily beta-amylase) activity and considerably higher ratios of beta- to alpha-amylase. In aerial tissues there was an inverse relationship between chlorophyll and starch concentration, and beta-amylase activity. In sections of petals and stems there was a pronounced inverse relationship between chlorophyll concentration and the activity of alpha-amylase. Senescing leaves of pea, as determined by age, and protein and chlorophyll content, contained 3.8-fold (fresh weight basis) and 32-fold (protein basis) higher alpha-amylase activity than fully mature leaves. Leaves maintained in darkness for 12 days displayed a 14-fold (fresh weight basis) increase in alpha-amylase activity over those grown under continuous light. In senescence and prolonged darkness studies, the alpha-amylase that was greatly increased in activity was the primarily apoplastic alpha-amylase. These studies indicate that there is a pronounced inverse relationship between chloroplast function and levels of apoplastic alpha-amylase activity and in some cases an inverse relationship between chloroplast density and/or function and vacuolar beta-amylase activity.