Effect of Endogenous Cytokinins in Strawberry Fruits on Their Maturing

Abstract

For the purpose of precise disccusion of the role of endogenous cytokinins on the development of strawberry fruits, this research was carried out to investigate the distribution of cytokinin-like substances in strawberry fruits and the changes of the activity in fruits during fruit development in relation to achene development.
1. Cytokinin activity was recognized in both the ethyl acetate phase and the aqueous phase which were extracted with ethyl acetate from the methanol extract of strawberry fruits. In a paper chromatography of the ammonia eluate fraction of the aqueous phase, cytokinin activity was detected at two regions, Rf 0.2-0.3 and Rf 0.6-0.8. On the other hand, in a column chromatography of the ethyl acetate fraction, the activity was recognized in one elution number (ethyl acetate 90%+methanol 10%).
2. The majority of total activity of cytokinins in strawberry fruits was contained in achenes.
3. Fruits grown at 20°C developed rapidly from 15 days after anthesis and matured 27 days after anthesis. Cytokinin activity in fruits was the highest 10-15 days after anthesis and decreased gradually as fruits developed. The achene of the fruits 10-15 days after anthesis was still immature as the ovule cavity was mostly occupied by the endosperm. On the other hand, the achene of the fruits 25 days after anthesis was mature as the ovule cavity was filled with the embryo.
4. The time of maturing of fruits grown at 20°C was delayed compared to that of fruits grown at 30°C. Fifteen days after anthesis, cytokinin activity in fruits grown at 20°C was much higher than that in fruits grown at 30°C, and the achene of the fruits grown at 20°C was still immature compared to that of the fruits grown at 30°C.
From these results, it is considered that cytokinin is actively produced in achenes when they are immature. Therefore, it is reasonable to consider that the time of maturing of fruits grown at lower temperature is suppressed because high cytokinin activity can be maintained in achenes for longer time due to their slow development.