Stimulatory effect of phytosulfokine-alpha on the proliferation of tobacco 'Bright Yellow 2' suspension cells.

'Bright Yellow 2' ('BY-2') tobacco (Nicotiana tabacum L.) suspension cells could not proliferate even with proper 2, 4-D concentration (0.6 mg/L) in the medium, when the initial cell density is low. However, the cells could divide and grow normally if conditioned medium (CM) was added to the medium, and the rate of proliferation of cells was proportional to the quantities of CM supplied. The same results were obtained, when the CM was replaced by synthesized phytosulfokine-alpha (PSK-alpha), a sulfated pentapeptide, PSK-alpha was found in CM of 'BY-2' cells by MS identification. From the significant linear relationship between rate of cell proliferation (measured by OD600 value) and concentrations (0.05 nmol/L-10 micromol/L) of PSK-alpha, it can be seen that the 'BY-2' suspended cells are the ideal plant material for bioassay of PSK-alpha. This result suggests that the PSK-alpha might be involved in promoting the proliferation of 'BY-2' suspension cells.