CYTOKININS IN THE XYLEM SAP OF THE DIOECIOUS FYNBOS SHRUB, LEUCADENDRON-RUBRUM BURM F - SEASONAL FLUCTUATIONS AND THEIR POSSIBLE INTERACTION WITH MORPHOLOGICAL-CHARACTERISTICS AS EXPRESSED IN THE 2 SEXES

Branches of male and female plants of the dioecious Leucadendron rubru m Burm. f. were collected on the site of the Weikamp weather-station i n the Jonkershoek State Forest, Stellenbosch, from July 1990 to Septem ber 1991. Xylem sap was extracted from the branches by vacuum extracti on. HPLC was employed to purify the xylem sap and to separate the cyto kinins prior to quantitation by ELISA. The cytokinin levels in the pur ified plant samples were determined using rabbit antiserum-based ELISA s for the determination of the levels of the cytokinins DHZR and IPA, and a trans-ZR specific monoclonal antibody-based ELISA for the determ ination of the levels of the cytokinin ZR. It was observed that the le vels of the cytokinins DHZR and ZR did not differ significantly betwee n male and female plants but did correlate with the seasonal growth pa tterns. The levels of the cytokinin IPA, in male and female plants of L. rubrum, not only correlated specifically with the different seasona l growth patterns observed but differed significantly between male and female plants. Peaks in the levels of all three cytokinins, i.e. ZR, DHZR and IPA, occurred during the study period. These peaks correspond ed with the phenological development of L. rubrum, specifically with v egetative bud break and inflorescence differentiation and appeared to be synchronized with the growth and development. An attempt was also m ade to correlate cytokinin levels with the extreme differences in morp hological characters exhibited by male and female plants, and possibly to explain to what extent these phytohormones influence sex expressio n in L. rubrum.