Distribution of Calcium, Potassium and Phosphorus in Helianthus annuus Hypocotyls and Zea mays Coleoptiles in Relation to Tropic Stimuli and Curvatures

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Abstract
Studies have been made of the distribution of 45Ca, 42K, total K+ and 32P between the concave and convex sides of segments of hypocotyl of Helianthus annuus and coleoptiles of Zea mays during curvatures induced by gravity, unilateral illumination or unilateral applications of indol-3yl acetic acid (IAA). The elements were fed to the roots of seedlings for a 3–4 h pretreatment period. Distributions in segments in intact seedlings were compared with those in explanted segments deprived of a continuing supply of the element concerned in order to separate possible differential transport of the element from the roots from any real movement across the organ from side to side. With all three treatments, and in both explants and intact plants, 45Ca concentrations (on both fwt and dwt bases) were higher on the convex side. There was evidence of differential transport to the two sides and also of a direct movement across the parenchyma from one side to the other. In organs where curvature was inhibited by low temperatures (4 °C in geotropic experiments) or by the antitropistic agent, N-1-naphthylphthalamic acid, no concentration differences arose between the two sides. After the tropic stimuli the onset of the concentration differences preceded the onset of curvature significantly, indicating that those differences were not caused by differential growth of the organ. The diuretic, mersalyl, applied unilaterally produced differences in element concentration of the same order and kind as similar treatment with IAA, but caused no growth curvatures. It is concluded that the movement of elements in tropically curving tissues, although apparently obligately-linked with curvature, is not the result of that curvature or its cause, but is in some as yet undefined way an outcome of auxin gradients in the tissue.