TISSUE-SPECIFIC LOCALIZATION OF ASPARTIC PROTEINASE IN DEVELOPING ANDGERMINATING BARLEY GRAINS

Resting seeds of several plant species, including barley grains, have been reported to contain aspartic proteinase (EC 3.4.23) activity. Her e, the expression of the Hordeum vulgare L. aspartic proteinase (HvAP) was studied in developing and germinating grains by activity measurem ents as well as by immunocytochemical and in-situ hybridization techni ques. Southern blotting suggests the presence of one to two HvAP-encod ing genes in the barley genome, while Northern analysis reveals a sing le 2.1-kb mRNA in grains and vegetative tissues. Western blotting with antibodies to HvAP shows the same subunit structure in different grai n parts. In developing grains, HvAP is produced in the embryo, aleuron e layer, testa and pericarp, but in the starchy endosperm HvAP is pres ent only in the crushed and depleted area adjacent to the scutellum. D uring seed maturation, HvAP-encoding mRNA remains in the aleurone laye r and in the embryo, but the enzyme disappears from the aleurone cells . The enzyme, however, remains in the degenerating tissues of the test a and pericarp as well as in resting embryo and scutellum. During the first three days of germination, the enzyme reappears in the aleurone layer cells but is not secreted into the starchy endosperm. The HvAP i s also expressed in the flowers, stem, leaves, and roots of barley. Th e wide localization of HvAP in diverse tissues suggests that it may ha ve several functions appropriate to the needs of different tissues.