Abstract
The effect of benzylaminopurine (BA) on the growth of young radish plants (Raphanus sativus L. cv. Riso Daikon) was studied and the possible role of cytokinins in the senescence of cotyledons of radish seedlings growing under water stress was examined.
1) BA application to the above-ground parts (foliage leaves, cotyledons, and hypocotyls) of plants resulted in the increase in the distribution ratio of photosynthetic product to hypocotyls and to leaves (foliage leaves and cotyledons), and the decrease in the distribution to roots. The effect of BA on the change of distribution ratio was not observed in the water-stressed plants, except for the application of higher concentrations of BA.
2) Yellowing and marked decrease in chlorophyll content were observed in the cotyledons of water-stressed plants. However, kinetin application could prevent the decrease in chlorophyll content in the cotyledons of water-stressed plants.
3) Since the decrease in chlorophyll content in the cotyledons of young radish plants with no visible foliage leaves did not occur under the water stress, yellowing may depend on the presence of growing foliage leaves.
4) Yellowing of cotyledons was observed when roots were removed but this phenomenon was not observed when kinetin was applied to the cut end of plants.
5) The cytokinin-like activity in the extract of the water-stressed plants was lower than that of the control ones.
