ELECTRICAL POLARITY AND AUXIN TRANSPORT

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Abstract
Cut sections of pea stems and oat coleoptiles were reversibly polarized by applied direct currents beyond certain thresholds of current. The normal electrical polarity could be reversibly increased, decreased, or reversed by these currents. Polarity was measured with an electrometer and non-polarizable electrodes, under controlled conditions, and resistance by electrometer and current measurements. Apical negativity (normal polarity) increased, within limits, on stimulation by alternating currents, but only after certain thresholds of applied currents were reached. Oat coleoptiles did not act as ohmic rectifiers of an alternating current, as claimed by Metzner for many plant tissues, nor did they display a unipolar re-sistance to a direct current. This means that a possible asymmetry in membrane permeability theoretically linked with polar transport of auxin (accumulation, secretion?) cannot be analyzed by simple unipolar or rectification measurements. The apical negativity of oat coleoptiles was reversibly decreased by ether narcosis, and the P.D. fell to that caused by gravity when narcosis was irreversible. The resistance of oat coleoptiles reversibly decreased on passage of small direct currents and alternating currents. The resistance followed the inherent P.D. changes, but in the opposite sense; i.e., when apical negativity increased, the ohmic resistance decreased. An exception occurred in complete irreversible ether narcosis, where both resistance and P.D. decreased. Polar heteroauxin transport in oat coleoptiles could be specifically abolished with 1 part of Na glyco-cholate in 100,000 parts of water, without there being any change in electrical polarity, respiration, semipermeability (turgor), growth by cell elongation, or protoplasmic streaming.[long dash]Lateral and longitudinal transport of auxin-a in plants are evidently caused by entirely different mechanisms, as shown by the opposite effects of light, gravity, applied potential differences, ethylene, and sodium glycocholate. The apparent relation of auxin transport in plants to ion accumulation by barley roots, as suggested by Went, is shown to be thrown into question; Na glycocholate abolished the former but not the latter. The above facts lend additional support to former statements made by the writer that electrical polarity, expressed in terms of inherent potential differences (unipolar conductance or alternating current rectification) has no apparent causal relation to polar auxin transport in plants.