Redistribution of Endogenous Cytokinins in Geotropically Stimulated Ribes nigrum Roots and Shoots

Abstract

Summary The occurence of cytokinins in extracts of both roots and shoots of Ribes nigrum was demonstrated by soybean callus bioassay and gas-liquid chromatography. Quantitative estimation of cytokinin activity in extracts from upper and lower halves of both roots and shoots which have been kept horizontal, and showed positive and negative curvatures after 4 h respectively, indicated a redistribution of endogenous cytokinins during geotropic stimulation. The ratio of the total cytokinins in roots in upper and lower halves was 2.9 : 1, whereas in shoots it was found to be 1 : 3.5, in favour of upper and lower halves respectively. In wheat roots, IAA was inhibitory to root-elongation within the first one and a half hours, whereas kinetin had a stimulatory effect during the same time. ABA was inhibitory at all times although the lowest concentration of 0.001 mg/l showed a non-significant stimulatory effect. GA 3 stimulated root-elongation of wheat seedlings within 2 hours. In wheat coleoptiles, IAA was inhibitory within the first hour, whereas GA 3 showed a stimulatory effect during the first one and a half hours. Kinetin had an inhibitory effect in the first hour, followed by a stimulatory effect after 2 hours. 100 mg/l had an inhibitory effect at all times. ABA inhibited the coleoptile at higher concentrations, whereas the lowest concentrations of 0.001 and 0.01 mg/l gave rise of a slight increase in coleoptile growth. This growth was less than that of the controls. 60 and 50% of 10 mg/1 kinetin treated roots and shoots of intact Vicia faba seedlings developed positive and negative geotropic curvatures respectively, whereas 50 and 100 mg/l kinetin prevented the process in both organs. These results suggest the possibility of a participation of endogenous cytokinins in addition to auxin in the development of both positive and negative geotropic curvatures.