The distribution of phosphorus, calcium and potassium ions in tropically stimulated organs

Abstract

The distribution of 45Ca, 42K and 32P was studied in the hypocotyls of Helianthus annuus and also in the coleoptiles of Zea mays in relation to geotropic stimulation and response. The concentration of calcium was higher in the upper side and the concentration of potassium and phosphorus was higher in the lower side of the hypocotyls placed in horizontal position. This differential distribution was correlated with the curvature. The redistribution of ions is not connected to geotropic perception since 0.5 hour horizontal orientation at 25 C and subsequent exposure at 4 C did not result in any redistribution. No differential distribution was observed in the hypocotyls placed in horizontal position when curvature was stopped by pre-treatment with NPA. After unilateral IAA application (0.1% W/W in lanolin) the concentration of calcium was higher in the concave side whereas the concentration of potassium and phosphorus was higher in the convex side. IAA probably affects the ion pumps via differential growth which results in redistribution of ions. In unilaterally illuminated coleoptiles illuminated (concave) side showed higher concentration of calcium, whereas shaded (convex) side showed higher concentration of potassium and phosphorus. NPA inhibited phototropic curvature as a result no differential distribution of ion was observed. Unilateral application of mersalyl (10-4M in hydrated lanolin) resulted some movement of calcium away from the donor side and movement of potassium into the donor side. Mersalyl affects the distribution of ions by altering ion pumps and its mechanism of ion pump operation must be different from that of IAA as mersalyl does not produce a differential growth response and the IAA effect is dependent on differential growth. Hence, the results show a correlation between differential distribution of ions and curvature. It is concluded, therefore, that differential distribution is probably caused by curvature.