Sequence of Key Events in Shoot Gravitropism

Publisher Website
Google Scholar
Abstract
It has recently been shown that asymmetric acid efflux is closely correlated with the gravitropic curvature of plant shoots and roots. Auxin (IAA) redistribution in shoots as the cause or result of asymmetric acid efflux was studied. When abraded sunflower (Helianthus annuus cv. Mammoth) hypocotyls are submerged in 20 mM neutral buffer, gravicurature is greatly retarded relative to 0.2 mM controls. In both buffer systems there is a similar redistribution of [3H]IAA toward the lower surface of gravistimulated sunflower hypocotyls. Graviperception initiates IAA redistribution, which in turn results in auxin-induced asymmetric H+ efflux across the shoot. This interpretation is reinforced by data showing the effects of removal of the epidermal layers (peeling), osmotic shock and morphactin treatment on gravicuryature and [3H]IAA redistribution. Peeling and osmotic shock inhibit gravicurature but not redistribution. Morphactin inhibits both processses but does not inhibit hypocotyl straight growth.