Abstract
Effects of ammonium- and nitrate-top dressing on cytokinin contents in the root exudate of rice plant were studied under the field condition. Nitrogen application to the soil resulted in a significant increases in the content of cytokinins in the root exudate. When the plant was top-dressed with nitrate form, total content of cytokinins increased more obviously than with ammonium one. Similar situation was also observed in the leaves after nitrogen fertilization. Degradation of chlorophyll in the leaves detached from the plant top-dressed with nitrogen were significantly retarded: the effect was more remarkable in the lower leaves than in the upper ones. Cultured roots secreted cytokinins into the external medium and their composition was very similar to that of the root exudate. The authors thank Dr. A. Nishi, of the Faculty of Pharmaceutical Sciences, the University of Toyama, for his many helpful discussion and suggestions during this work.
