Multiple molecular forms of β-amylase in seeds and vegetative tissues of barley

The molecular forms of β-amylase present in developing, mature, germinating and malted grains of barley (Hordeum vulgare L.), and in vegetative tissues, have been studied using Western-blot analyses and isoelectric focusing of isoenzymes. Five isoforms with different relative molecular masses (Mrs) could be recognised. The major isoform present in the mature grain, called isoform B, had an Mr of about 60 000. This was converted on malting or germination to two lower-Mr forms called C and D. Previous work (R. Lundgard and B. Svensson, 1986, Carlsberg Res. Commun. 51, 487-491) has shown that these result from partial proteolysis of isoform B. Isoenzyme analyses showed complex patterns of bands, with pIs between about 5.0 and 6.0. Two allelic types were present in the eight lines. A number of new bands with a range of pIs appeared during germination and malting.An isoform with the same Mr as D and a minor low-Mr isoform (E) were present in young developing whole caryopses (8-12 d after anthesis), but not in older developing endosperms (14-21 d after anthesis). Isoenzyme analyses also showed different patterns of bands in these two tissues, while hybrid-dot analyses indicated the presence of separate populations of mRNAs. It is suggested that the early endosperm isoforms (D and E) are "green" β-amylases present in the pericarp and-or testa of the young caryopses.Roots but not shoots or leaves also contained an isoform with the same Mr as D, although the pattern of isoenzymes differed from that present in the seed tissues.The fifth isoform, A, was a diffuse high-Mr form present in small amounts in all seed and vegetative tissues, and may correspond to a constitutively expressed form.These multiple molecular forms of β-amylase are discussed in relation to the recent report that β-amylase is encoded by two structural loci, with a total copy number of two to three per haploid genome (Kreis et al, 1988, Genet. Res. Camb. 51, 13-16).