Abstract
Two cDNA clones were characterized which correspond to different RNA species whose level is increased by gibberellic acid (GA3) in barley (Hordeum vulgare L.) aleurone layers. On the criteria of amino terminal sequencing, amino acid composition and DNA sequencing it is likely that one of these clones (pHV19) corresponds to the mRNA for α-amylase (1,4-α-D-glucan glucanohydrolase, EC 3.2.1.1.), in particular for the B family of α-amylase isozymes (Jacobsen JV, Higgins TJV: Plant Physiol 70:1647-1653, 1982). Sequence analysis of PHV19 revealed a probable 23 amino acid signal peptide. Southern hybridization of this clone to barley DNA digested with restriction endonucleases indicated approximately eight gene-equivalents per haploid genome.The identity of the other clone (pHV14) is unknown, but from hybridization studies and sequence analysis it is apparently unrelated to the α-amylase clone.Both clones hybridize to RNAs that are similar in size (∼1500b), but which accumulate to different extents following GA3 treatment: α-amylase mRNA increases approximately 50-fold in abundance over control levels, whereas the RNA hybridizing to pHV14 increases approximately 10-fold. In the presence of abscisic acid (ABA) the response to GA3 is largely, but not entirely, abolished. These results suggest that GA3 and ABA regulate synthesis of α-amylase in barley aleurone layers primarily through the accumulation of α-amylase mRNA.
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