Isolation and characterization of cDNAs coding for leaf-specific thionins closely related to the endosperm-specific hordothionin of barley (Hordeum vulgare L.)

Summary In etiolated barley seedlings a highly abundant mRNA encoding a 15 000 M_r polypeptide is present whose concentration rapidly declines upon illumination. The amino acid sequence of the 15 000 M_r polypeptide has been deduced from cDNA sequences and the polypeptide has been identified as a high-molecular-weight thionin precursor. Closely related thionins, most of them highly toxic, have been described previously in several higher plants. In cereals the occurrence of these thionins has been thought to be confined to the seeds. Our present data demonstrate that, in additon to endosperm-specific hordothionin mRNA, a closely related but distinct second group of thionin mRNAs is present in the barley leaf during early seedling development. Since the appearance of the bordothionin mRNA is not controlled by light, two different gene families for thionins exist whose expression seems to be under a different mode of developmental control.Dedicated to Prof. W. Halbsguth on the occasion of his 75th birthday