DIFFERENTIAL EXPRESSION OF 2 BETA-AMYLASE GENES OF RYE DURING SEED DEVELOPMENT

The expression of two beta-amylase loci was analysed in the developing seeds of two inbred lines of rye (Secale cereale L.), one of which wa s a beta-amylase deficient mutant. Enzymatic activity and the contents of enzymatic protein and mRNA specific for each of an endosperm-chara cteristic and ubiquitous beta-amylase were determined throughout the c ourse of caryopsis development. Both loci were expressed in the develo ping normal line caryopses according to different temporal and quantit ative patterns. The ubiquitous enzyme-specific locus beta-Amy 2 was ex pressed earlier; both mRNA and enzymatic protein accumulated to a maxi mum extent at 10 to 15 days after pollination. In contrast, the highes t content of mRNA for endosperm beta-amylase (encoded by the beta-Amy 1 locus) was found 20 days after pollination, and the corresponding en zymatic protein accumulated throughout seed development. The expressio n of the beta-Amy 1 locus was 30- to 40-fold higher than that of the b eta-Amy 2 locus in terms of maximum specific mRNA accumulation. The ex pression product of only the beta-Amy 2 locus was found in the develop ing mutant line caryopses. The expression pattern of this locus was si milar in the developing normal and mutant line seeds in terms of the t emporal accumulation of mRNA and enzymatic protein. However, an approx imately 4-fold higher level of ubiquitous beta-amylase-specific mRNA w as found in the mutant than in the normal line caryopses, and the cont ent of ubiquitous beta-amylase protein decreased to near zero at seed maturity in the mutant line, but not in the normal line, caryopses. Th e enzymatic activities of both beta-amylases appeared to be regulated at the level of accumulated enzymatic protein.