The Cytoplasmic Streaming Response of Tomato Root Hairs to Auxin; the Role of Calcium

Abstract

The effects of IAA on the cytoplasmic streaming response of tomato root hairs were observed at different external calcium concentrations. The sensitivity of tomato root hairs to IAA was increased by increasing the calcium content of the bathing medium; lower concentrations of IAA were needed to stimulate cytoplasmic streaming at high [Ca²⁺]_ext. The transplasma membrane electrical potential difference was rapidly depolarised by IAA across a wide range of auxin and calcium concentrations; subsequent hyperpolarisation was only seen in the presence of high [Ca²⁺]_ext. Measurements of cytoplasmic calcium levels, using the dye fluo-3, revealed the dynamic nature of the cytoplasm. As in earlier experiments, in which indo-1 and fura-2 were used, IAA appeared to have only small effects on [Ca²⁺]_cyt. Clear, auxin-induced changes in [Ca²⁺]_cyt were recorded only under non-physiological conditions.