Relationship of Isozyme Genotypes of AGP with Activity of AGP and Starch Content in Wheat Grain

Abstract

ADP-Glucose pyrophosphorylase(AGP) controls a rate-limiting step in the starch biosynthesis in developing wheat(Triticum aestivum L.) seeds,therefore,determinately affecting seed sink strength. Evidence is presented for the existence of AGP isozymes in common wheat endosperm. Following an approach already shown to be successful in maize(Zea mays L.),native polyacrylamide gel electrophoresis(native PAGE) was designed to identify AGP isozyme patterns from crude enzyme prepara-tions. To explore the relationship of isozyme genotypes with the starch content in wheat grains,activity of AGP and starch content were measured in 60 cultivars from 17 provinces in China. The results showed that there were four alleles,namely AGPa,AGPb,AGPc,and AGPd,with frequencies of 96.7%,80.0%,86.7%,and 16.7%,respectively. Five genotypes were determined in which AGPabc took on the highest frequency of 46.7% and AGPbc took on the lowest frequency of 3.3%. The activity of AGP and starch content in the cultivars with distinct genotypes were significantly different(P0.05). The cultivars with genotype AGPabcd and AGPabc showed a high value of AGP activity and starch content. The lack of AGPa,AGPb,or AGPc in cultivars resulted in a low value of AGP activity and starch content. It indicated that different genotypes of AGP isozyme show distinct genetic impact on enzyme activity and starch content in common wheat.