THE CYTOKININS AS ENDOGENOUS GROWTH-REGULATORS IN MACROCYSTIS-PYRIFERA (L) C AG (PHAEOPHYCEAE)

Cytokinin-like activity has been detected in the giant kelp, Macrocystis pyrifera (L.) C. Ag. This activity was monitored on both a quantitative and qualitative basis within regions of a young blade, between blades of different ages and in young blades on a seasonal basis. Growth studies were made on young, mature and aged blades in situ (on a monthly basis in young blades), and along the length of young blades (both in vitro and in situ). The total cytokinin-like activity was highest in the basal third of the young blade, which contains the intercalary meristem and is the most rapidly growing portion of the blade. The rapidly growing young blade contained high levels of Cytokinins as free bases and ribosides but low levels of putative cytokinin 0-glucosides, whereas the disintegrating aged blade contained high levels of the cytokinin O-glucosides and low levels of the free bases and ribosides. The highest totals of cytokinin-like activity occurred in autumn (April) and spring (October) and corresponded with the observed periods of maximum growth. The cytokinin-like activity was predominantly in the free base or riboside form. Lower levels of cytokinin-like activity were detected in winter (July) and even lower levels in summer (January), corresponding with the very low growth rates in summer and the trend towards decreased growth rates in winter. In winter and summer, most of the cytokinin-like activity was contained in the cytokinin O-glucosides. © 1990, Walter de Gruyter. All rights reserved.