Abstract
Summary Ca 2+ -channel blockers, verapamil and diltiazem, strongly inhibited IAA-induced elongation of sunflower ( Helianthus annuus L.) hypocotyl segments. Pretreatment with Ca 2+ -channel blockers (0.1 mM verapamil or diltiazem) inhibited the initiation of IAA-induced elongation, but not fusicoccin-induced elongation. Verapamil, when applied 60 min after IAA, began to reduce the steady-state elongation rate with a short lag time of ca. 10 min. This inhibition of elongation by Ca 2+ -channel blockers was antagonized by Ca 2+ pretreatment even at low concentration (less than 50 μM). Cations such as Mn 2+ , Mg 2+ , K + , and Na + also showed the antagonism with respect to the inhibitory effect of the blockers, whereby the effect of divalent cations was much more effective than monovalent cations. The antagonism of Ca 2+ against the inhibitory effect of the blockers occurred optimally at a specific Ca 2+ concentration. These results suggest that Ca 2+ and Ca 2+ -channel blockers competitively interact against the Ca 2+ channel and that calcium flux through Ca 2+ channels plays an important role in auxin-induced cell elongation.
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