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

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Abstract
When the esterase substrate .alpha.-naphthyl acetate is added to segments from coleoptiles of oat (Avena sativa L., cv. Victory) or corn (Zea mays L., cv. Bear hybrid WF 9 .times. 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. 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.