Studies on endogenous cytokinins inCitrus

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Abstract
Cytokinin amounts were determined in the ovaries of flowers and fruitlets on leafy and leafless inflorescences of seeded and seedless cultivars of Citrus sinensis, C. reshni and C. clementine. Flowers were sampled over a 65 day period from before anthesis to after fruit set, during the period from fructification to fruitlet expansion. Cytokinin activity appeared in both organic and aqueous phases obtained in the extraction process. Generally, the maximum activity in the organic phase occurred at anthesis, except in ‘Navelate’ orange, and decreased sharply following petal fall, whereas the aqueous phase had more cytokinins later, when the fruitlets had reached 1-2 cm diameter. The effect of pollination on cytokinin-like compounds was studied in seeded cultivars. The pollinated ovaries showed a peak in cytokinin activity at anthesis, in contrast to unpollinated ovaries. Partition chromatography of the organic phase on Sephadex LH-20 indicated five zones of cytokinin activity, four of which had the same elution volumes as ribosyl zeatin, zeatin, isopentenyl adenosine and isopentenyl adenine.

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