Nonhormonal induction of H efflux from plant tissues and its correlation with growth.

When the esterase substrate alpha-naphthyl acetate is added to segments from coleoptiles of oat (Avena sativa L., var. Victory) or corn (Zea mays L., Bear hybrid WF 9 x 38) or to roots of lentil (Lens culinaris Med.), it is rapidly taken up and hydrolyzed to alpha-naphthol and acetic acid. This technique was used to generate intracellular acid and to study the effect of its efflux on growth. With corn coleoptile segments, treatment with alpha-naphthyl acetate induced more rapid and more prolonged growth than did exposure to external acidic buffers. Dose-response studies of alpha-naphthyl acetate induction of H(+) secretion and growth indicated the existence of a distinct threshold rate of H(+) efflux below which growth is not enhanced. The rate of H(+) efflux induced by optimal levels of auxin appears to be at or below this threshold level in corn coleoptile tissue. These data indicate that the relationship between external acidification and elongation is not a simple one and that the effectiveness of H(+) entering the cell wall may depend on factors not directly correlated with the appearance of H(+) in the external medium.