Polar Transport of Auxin and Electrical Polarity in Coleoptile of Avena.

In the introduction to a recent paper by the writer (5), -the phenomenon of the polar transport of auxin in plants was briefly discussed. It was indicated there that the electrical theory of the polar transport of auxin was one of the most widely accepted ones. This theory states that the inherent electrical polarity of plants is the cause of the longitudinal polar transport of the negative ion of auxin, the plant-growth hormone, to an inherent positive pole in the plant. It was concluded (5) that an electrical polarity exists in seedlings. Apices are electronegative to basal regions in seedlings of Impatiens, Avena, Zea, Pisum, and Vicia. In Avena, this polarity exists internally as well as on the surface of the cuticle. It is thus seen that the electrical polarity found in seedlings conforms with that demanded by the electrical theory of the polar transport of auxin. Cut sections of these seedlings exhibited the same electrical polarity as intact plants, i.e., electronegativity of the morphological apical cut surface. But it was also shown that this section-polarity could be inverted by gravity; and Clark (4) showed that the electrical polarity of the Avena coleoptile could be altered or inverted by light. Thus the electrical theory of polar transport is directly contradicted by the fact that neither light nor gravity affect the longitudinal transport of auxin (See "Discussion" and 5). The present article is concerned with experiments in which attempts were made to link polar transport and electrical polarity. Auxin transport and electrical polarity were measured at the same time, and then the electrical polarity was altered by applied potentials and by gravity to see if there were any parallel changes in polar transport.