Cytokinin profiling of long-term in vitro pea (Pisum sativum L.) shoot cultures

Forty-seven endogenous cytokinin metabolites were determined in samples of long-term in vitro multiple shoot cultures of pea (Pisum sativum L.). Significant differences were found in the levels of all cytokinin groups except cis-zeatin and some of its derivatives. Old cultures (30 or 10 years old) contained larger total and active cytokinin pools than freshly prepared cultures. Long-term shoot cultures maintained on cytokinin-supplemented media initially exhibit gradually increasing concentrations of endogenous cytokinins that subsequently stabilise at a high level, which can make it more difficult to induce rooting later on. This is consistent with previous findings concerning the growth and development of plantlets derived from long-term cultures and the generally accepted role of cytokinins during root development. The results presented herein demonstrate the utility of long-term pea cultures as model systems for studying the influence of long-term cultivation on genetic stability, and suggest ways of circumventing the rooting problems associated with such cultures.