Cytokinin activity was detected in the culture medium of Vinca rosea (Catharanthus roseus (L.) G. Don) crown-gall tumour tissue 1 week after subculture. Activity increased with time, reaching a plateau at 5-6 weeks. The cytokinin activity from extracts of staled culture medium after 1 and 2 weeks culture cochromatographed with zeatin, zeatin riboside and their dihydro derivatives. An additional slow-moving peak of cytokinin glucoside-like activity was observed from 3 weeks after subculture, and was detectable even at the end of a 10-week culture period.
When [U-14C]adenine was supplied to V. rosea crown-gall tissue, analysis of radioactivity remaining in the medium showed incorporation of label into zeatin and zeatin riboside (trans-isomers only) after only 1 h of incubation. Radioactivity in these compounds increased with time; peaking at 8 h, and was still detectable 125 h after incubation. At no time was radioactivity detected in dihydrozeatin, isopentenyladenine or their ribosides. At the end of 125 h incubation, less than 0.2% of radioactivity supplied initially was still present as adenine in the medium.
Significant inhibition of tissue growth occurred when it was cultured on medium supplemented with a synthetic or naturally occumng cytokinin.
