CONTRIBUTION OF SUCROSE SYNTHASE, ADP-GLUCOSE PYROPHOSPHORYLASE AND STARCH SYNTHASE TO STARCH SYNTHESIS IN DEVELOPING PEA-SEEDS

Using genetic variability existing amongst nine pea genotypes (Pisum s ativum L.), the biochemical basis of sink strength in developing pea s eeds was investigated, Sink strength was considered to be reflected by the rate of starch synthesis (RSS) in the embryo, and sink activity i n the seed was reflected by the relative rate of starch synthesis (RRS S), These rates were compared to the activities of three enzymes of th e starch biosynthetic pathway [sucrose synthase (Sus), ADP-glucose pyr ophosphorylase and starch synthase] at three developmental stages duri ng seed filling (25, 50 and 75% of the dry seed weight), Complete sets of data collected during seed filling for the nine genotypes showed t hat, for all enzyme activities (expressed on a protein basis), only Su s in the embryo and seed coat was linearly and significantly correlate d to RRSS, The contribution of the three enzyme activities to the vari ability in RSS and RRSS was evaluated by multiple regression analysis for the first two developmental stages, Only Sus activity in the embry o could explain, air least in part, the significant variability observ ed for both the RSS and the RRSS at each developmental stage, We concl ude that Sus activity is a reliable marker of sink activity in develop ing pea seeds.