Exogenously Applied Polyamines Reduce Reactive Oxygen Species, Enhancing Cell Division and the Shoot Regeneration from Brassica oleracea L. var. capitata Protoplasts

Polyamines (PAs) are organic molecules that are found in plants and animals. In plants, they are involved in the regulation of cellular growth, apoptosis, rooting, flower development, and stress responses. The effect of exogenously applied polyamines on the development of Brassica oleracea L. var. capitata protoplast cultures was studied. Protoplasts were isolated from hypocotyls of 2-week-old seedlings of three accessions and they were cultured in liquid media supplemented with putrescine (Put), spermidine (Spd), and spermine (Spm) at concentrations of 0 (control), 10, 20, and 40 mu M. In the very early culture (24 and 48 h), cellular reactive oxygen species levels (ROS) in live cells were monitored using a fluorescent probe. The Put- and Spd-treated protoplasts exhibited lower fluorescence intensities, which corresponded to lower ROS accumulation as compared to the PA-free control. The protoplast viability was affected by the type of polyamine applied rather than its concentration. Put and Spd had a beneficial effect on the mitotic activity of the cultured cells, which was observed in all tested accessions. The highest frequency of shoot organogenesis (21%) was obtained from microcalli derived from the protoplasts cultured on the medium supplemented with 10 mu M Put. Analysis of the ploidy level of the regenerants showed that the vast majority were diploids. Our results demonstrated that exogenously applied PAs maintained the viability of B. oleracea L. var. capitata protoplasts by alleviating oxidative stress and stimulating mitotic activity, which further affected the plant regeneration process.