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

Abstract

Phytosulphokine-α (PSK-α) is the first chemically characterized peptide that acts as a plant growth factor. It stimulates the proliferation of asparagus and rice cells, but no information is yet available on its effects on plant morphogenesis. The effects of PSK-α on somatic embryogenesis in carrot (Daucus carota L.) were examined. PSK-α, when added to the induction medium for somatic embryogenesis, increased the number of somatic embryos. The chemical analogues [2-5]PSK-α and tyrosine sulphate ester (Tyr-SO3 H), which have been used as negative controls in other systems, had no effect. Moreover, the proliferation of cells during somatic embryogenesis was also enhanced by PSK-α. These results indicate that PSK-α enhanced cell division and, as a consequence, stimulated carrot somatic embryogenesis. PSK-α 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-embryogenic cells (cells that had lost the ability to form somatic embryos) in medium without 2,4-D. These results indicate that PSK-α has a stimulatory effect on cell division generally in carrot cell cultures.