The Electrical Control of Growth in Plant Tissue 7

Goldsworthy, A. and Rathore, K. S. 1985. The electrical controlof growth in plant tissue cultures: The polar transport of auxin.—J.exp. Bot. 36: 1134–1141. The reasons for a many-fold stimulation of shoot formation anda 60–70% stimulation of growth in tobacco callus causedby passing a very weak electric current (1 or 2 µA) betweenthe callus and the culture medium have been investigated. Thestimulation of callus growth occurred only when the callus wasmade negative to the medium and then only when IAA was added.It was abolished, even in the presence of IAA, by the additionof TIBA which is an inhibitor of polar auxin transport, andalso when the IAA was substituted by either IAN or the syntheticauxin 2,4-D, neither of which show significant polar transport.This suggests that the electrical treatment may have alignedthe physiological polarities of the callus cells so as to promotethe polar transport of IAA into the tissue when the callus wasnegative to the medium. If so, the enhanced shoot formationmay have been due to the parallel orientation of the growthaxes of individual cells so as to make the production of organformingmeristems more likely. The mechanism of the effect and its relationshipto the natural forces controlling differentiation is discussed. Key words: —Auxin, electrophysiology, polarity, tissue-culture, tobacco, transport