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

Abstract

Cells in culture with a high cell density can proliferate in medium that contains phytohormones, but cells at low Phytosulphokine-a (PSK-a) is the first chemically char- cell density cannot. However, cells at a low cell density acterized peptide that acts as a plant growth factor. can grow in the presence of conditioned medium (Stuart It stimulates the proliferation of asparagus and rice and Street, 1969; Somers et al., 1987; Birnberg et al., cells, but no information is yet available on its effects 1988; Bellincampi and Morpurgo, 1987, 1989; Huang on plant morphogenesis. The effects of PSK-a on et al., 1990; Bellincampi et al., 1993). None of the somatic embryogenesis in carrot (Daucus carota L.) phytohormones characterized to date is able to substitute were examined. PSK-a, when added to the induction for the conditioned medium. Thus, it was postulated medium for somatic embryogenesis, increased the that certain factors accumulate in conditioned medium number of somatic embryos. The chemical analogues and promote the division of cells cultured at low cell [2‐5]PSK-a and tyrosine sulphate ester (Tyr-SO 3 H), density. Matsubayashi and Sakagami (1996) isolated which have been used as negative controls in other phytosulphokine-a (PSK-a) as such a factor from the systems, had no effect. Moreover, the proliferation conditioned medium of a culture of mesophyll cells of of cells during somatic embryogenesis was also Asparagus oYcinalis L. PSK-a was determined to be a enhanced by PSK-a. These results indicate that PSK- sulphated pentapeptide: H-Tyr(SO