The role of free space calcium in the basipetal transport of indole‐3‐acetic acid in sunflower hypocotyls1

Abstract

Abstract Calcium has been reported to be involved in the basipetal transport of indole‐3‐acetic acid (IAA). It has been suggested that basipetal transport of IAA requires the influx of Ca2+ into the cytoplasm from the cell wall free space and that Ca2+ acts as a second messenger. Experiments were conducted to determine the interaction of free space Ca2+ with the basipetal transport of IAA. Four day old sunflower (Helianthus annus L. cv ‘Russian Mammoth') seedlings grown in 0.20 strength Hoagland's solution were either left intact or excised below the cotyledonary node to remove the meristem, the source of IAA in the shoot. After removal of the node, the plants were treated with or without 500 μM IAA in lanolin paste. After 24 h, 3 mm segments were cut from the hypocotyls and incubated in KCl. Solution Ca2+ concentration, representing free space Ca2+, increased when the source of IAA was removed. Plants which were provided a source of IAA, either endogenously or exogenously, had low levels of free space Ca...