Phytosulphokine-alpha, a peptidyl plant growth factor, stimulates somatic embryogenesis in carrot

Phytosulphokine-alpha (PSK-alpha) is the first chemically char characterize d peptide that acts as a plant growth factor. It stimulates the proliferati on of asparagus and rice cells, but no information is yet available on its effects on plant morphogenesis, The effects of PSK-alpha on somatic embryog enesis in carrot (Daucus carota L.) were examined, PSK-alpha, when added to the induction medium for somatic embryogenesis, increased the number of so matic embryos. The chemical analogues [2-5]PSK-alpha and tyrosine sulphate ester (Tyr-SO3 H), which have been used as negative controls in other syste ms, had no effect. Moreover, the proliferation of cells during somatic embr yogenesis was also enhanced by PSK-alpha. These results indicate that PSK-a lpha enhanced cell division and, as a consequence, stimulated carrot somati c embryogenesis. PSK-alpha also stimulated the proliferation of embryogenic cells in medium that contained 2,4-dichlorophenoxyacetic acid (2,4-D), in which somatic embryos did not form, as well as the proliferation of non-emb ryogenic cells (cells that had lost the ability to form somatic embryos) In medium without 2,4-D, These results indicate that PSK-alpha has a stimulat ory effect on cell division generally in carrot cell cultures.