CORRELATIONS BETWEEN PROTON-EFFLUX PATTERNS AND GROWTH-PATTERNS DURING GEOTROPISM AND PHOTOTROPISM IN MAIZE AND SUNFLOWER

By placing seedlings of sunflower (H. annuus L.) or maize (Z. mays L.) on agar plates containing a pH indicator dye, surface pH patterns along the growing seedling may be observed through color changes of the indicator dye. In geotropically stimulated sunflower hypocotyls or maize coleoptiles there is enhanced proton efflux on the lower surface of the organ prior to the initiation of curvature. As curvature develops the pattern of differential acid efflux becomes more intense. A similar phenomenon is observed when these organs are exposed to unilateral illumination, i.e., enhanced acid efflux occurs on the dark side of the organ prior to the initiation of phototropic curvature and the pattern of differential acid efflux intensifies as phototropic curvature develops. Apparently, differential acid efflux occurs in response to tropistic stimuli and the acid efflux pattern may mediate the development of tropistic curvatures.