The promotive effects of a peptidyl plant growth factor, phytosulfokine-α, 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 higher plant to be characterized. They induce the proliferation in suspension culture of mesophyll cells of asparagus (Asparagus officinalis L.; Matsubayashi and Sakagami 1996b). We examined the effects of PSK-α on the formation of adventitious roots on cucumber hypocotyls. The number of roots increased 2- to 2.5-fold after treatment with PSK-α but derivatives of PSK-α were inactive in our assay system. The effect of PSK-α on the formation of adventitious roots was also examined in terms of the expression of a newly isolated gene for a root-specific cystatin of cucumber (RCC). The results indicate that PSK-α can promote organogenesis in plant, acting possibly via enhancement of the proliferation of plant cells.