Modulation of chloroplast movement in the green alga Mougeotia by the Ca2+ ionophore A23187 and by calmodulin antagonists.

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Abstract
The Ca2+ ionophore A23187 can induce chloroplast rotation within a single nonirradiated Mougeotia cell. The induced turning was dependent on the position of ionophore application and Ca2+ in the external medium. The role of calmodulin in mediating light-induced chloroplast rotation in the alga Mougeotia was investigated by using the paired calmodulin-antagonist drugs W5-W7 and W12-W13. In each pair, the antagonist with the greater affinity for calmodulin had the greater inhibitory effect on the phytochrome-controlled light response. Ca apparently functions as a chemical messenger to couple the stimulus of phytochrome photoactivation with physiological responses in plants.