THE PROMOTIVE EFFECTS OF A PEPTIDYL PLANT-GROWTH FACTOR, PHYTOSULFOKINE-ALPHA, ON THE FORMATION OF ADVENTITIOUS ROOTS AND EXPRESSION OF A GENE FOR A ROOT-SPECIFIC CYSTATIN IN CUCUMBER HYPOCOTYLS

Phytosulfokines (PSKs) were the first peptidyl growth factors from a h igher plant to be characterized. They induce the proliferation in susp ension culture of mesophyll cells of asparagus (Asparagus officinalis L.; Matsubayashi and Sakagami 1996b). We examined the effects of PSK-a lpha on the formation of adventitious roots on cucumber hypocotyls. Th e number of roots increased 2- to 2.5-fold after treatment with PSK-al pha but derivatives of PSK-alpha were inactive in our assay system. Th e effect of PSK-alpha an the formation of adventitious roots was also examined in terms of the expression of a newly isolated gene for a roo t-specific cystatin of cucumber(RCC). The results indicate that PSK-al pha can promote organogenesis in plant, acting possibly via enhancemen t of the proliferation of plant cells.