Polarity of Transport of Benzyladenine, Adenine and Indole-3-acetic Acid in Petiole Segments of Phaseolus vulgaris

Abstract

Polarity in plant tissues is recognizable externally from the pattern of growth. For example, segments of stem tissues suitably cultured produce buds only toward the ends which are nearest to the apex in the intact stem, while root initials are normally produced only at the opposite or basal ends. Within the tissues of young shoots polarity is manifested by a greater movement of endogenous or applied auxin in the basipetal direction, away from the apex, than in the acropetal direction, towards the apex. Until 1964, only the natural or synthetic auxins were known to move in this polar way. The relative concentrations of auxins and other hormonal regulators of growth, control the development of different plant parts. Examples of interactions between auxins and kinins include regulation of growth and differentiation in plant tissue culttures (11) and the control of apical dominance and lateral b)ud growth (6). It is, therefore, pertinent to consider the movement of kinins in plant tissues, and how this movement might be influenced by auxin. The observation that 1 kinin, benzyladenine (BA) is transported in petiole segments of Phaseolus vulgaris in a basipetally polar direction and that this movement is enhanced by indole-3-acetic acid (IAA) has already been reported briefly for benzyladenine labeled in 2 different positions (8, 9). Kinin activity in plants is shown by many 6-substituted adenine compounds (6) and it would appear that the adenine moiety is essential for such activity. Adenine itself, however, is poorly active in evoking a kinin response (11). The present paper reports the results of experiments on the transport of C14-labeled benzyladenine, adenine and indole-3-acetic acid which emphasize the difference in mobility between benzyladenine and adenine and provide evidence for an interaction between the movement of auxins and kinins.