Abstract
Peptidyl plant growth factor phytosulfokine-α (PSK-α) is known to stimulate both cell proliferation and differentiation, the mechanism for which, however, has yet to be elucidated. We here investigated the effects of PSK-α on cell cycle regulation using non-embryogenic cell cultures of carrot. Flow cytometric analysis of cell nuclear DNA content showed that the addition of PSK-α (1x10-7 M) to a medium containing a low concentration (4.5x10-7 M) of 2, 4-dichlorophenoxyacetic acid (2, 4-D) promoted progression of the G1 cell cycle. Similar results were obtained with a high 2, 4-D (4.5x10-6 M) medium lacking PSK-α. PSK-α appeared to be involved in cell cycle progression outside the G1 phase. RT-PCR using cell cycle-related genes from carrot showed that the amounts of the transcripts of these genes were increased by the addition of PSK-α, and the levels of which were very similar to those with high 2, 4-D medium. The timing of the transcript increase roughly corresponded to that of the cell cycle progression. PSK-α seemed to stimulate re-entry of quiescent cells into the cell cycle. We propose a mechanism that PSK-α stimulates cell proliferation through the cell cycle regulation.
