Genes with homologies to known α-galactosidases are expressed during senescence of barley leaves

alpha-Galactosidase activity increases during dark induced senescence as well as during natural senescence under field conditions. Two cDNA clones named pHvSF11 and pHvSF23 were isolated from a cDNA library of senescent barley flag leaves by screening with a coffee bean alpha-galactosidase cDNA as probe. Sequences of the two barley cDNAs show high homology to those of known alpha-galactosidases and hence seem to represent two different alpha-galactosidase genes in barley. Expression of the genes corresponding to HVSF11 and HvSF23 was analyzed on one hand in primary foliage leaves incubated in darkness to accelerate senescence and on the other hand in flag leaves from barley plants grown under field conditions. The transcript represented by the cDNA HvSF23 is detectable in fully expanded leaves and its level is slightly upregulated during dark induced senescence of primary foliage leaves as well as during natural senescence of flag leaves. In contrast, the level of the transcripts represented by the cDNA HVSF11 decreases in flag leaves during natural senescence and inversely increases in primary foliage leaves induced to senesce by darkness. Antibodies raised against overexpressed peptide sequences deduced from the two different partial cDNA sequences react with the same proteins. In extracts from primary foliage leaves induced to senesce by prolonged darkness two proteins were immunodecorated by these antibodies. In senescent flag leaves from a barley field an additional third protein was detected.