Early studies on the effect of peptide growth factor phytosulfokine-α on Brassica oleracea var. capitata L. protoplasts

Phytosulfokines (PSK) are peptidyl growth factors with the potential of inducing cell proliferation. We examined the effect of supplementation of liquid culture medium with 0.1 mu M phytosulfokine-alpha (PSK-alpha) on protoplast viability and division frequencies in seven accessions of Brassica oleracea var. capitata L., including cultivars and breeding lines. Protoplasts were isolated from leaves and hypocotyls of in vitro grown plants and immobilized in calcium-alginate layers. Cabbage protoplast-derived cells cultured in medium supplemented with 0,1 mu M of PSK-alpha had higher viability and division frequencies compared to cells cultured in PSK-alpha-free control medium. The effect of PSK-alpha was more pronounced in low-responding accessions ('Slawa z Golebiewa', 'Ramkila F1', LM, and LM98); however, in two cultivars with very low response ('Badger Shipper' and 'Oregon 123'), although the division frequencies in the media supplemented with PSK-alpha were increased over the control, the differences were not significant. Obtained callus colonies were subjected to regeneration. PSK-alpha supplemented into the liquid culture medium had an indirect effect on shoot regeneration by inducing sustained cell divisions leading to an increase in shoot regeneration in Slawa z Golebiewa and both breeding lines.