Distribution of Phytohormones among Different Plant Organs Determines the Development of Competitive Sinks in Radish Plants

Abstract

Phytohormones are known to mediate many responses of plants to changes in environmental cues including light climate. Light quality governs various stages of plant growth and development (Short and Briggs, 1994; Smith, 1995). One of the most important features of plant photoregulation is involvement of light quality in the determination of sink strength (Aksenova et al., 1994). Several sinks, such as newly developing leaves, petioles and stem, and storage organ(s) compete for photosynthetic metabolites in a plant. Some plant organs dominate others in their ability to attract assimilates from donor leaves, depending on their sink strength (Drozdova et al., 1987). Correspondingly, various hormones have been proposed to stimulate metabolite flow to above- and/or underground plant organs (Palmer and Smith, 1969; Metzger, 1988). It is possible therefore, that light quality changes the direction of assimilate flow in a plant through alterations in hormonal status of plant organs. We show here that hormones belonging to different classes (gibberellins, cytokinins, and auxin) act in concert to determine preferential development of either above-ground sink (petioles and stem) under red light (RL) or underground sink (storage organ) under blue light (BL).