Comparison between Swelling of Etiolated Wheat ( Triticum aestivum L.) Protoplasts Induced by Phytochrome and α-Naphthaleneacetic acid, Benzylaminopurine, Gibberellic acid Abscisic acid and Acetylcholine

Abstract

Summary Swelling of mesophyll protoplasts isolated from dark-grown wheat ( Triticum aestivum L.) can be induced if 0.5 mM Ca 2+ is present in the medium, by red light and hormones, e.g. α-naphthaleneacetic acid, benzylaminopurine, gibberellic acid, abscisic acid and acetylcholine (ACh). In the absence of Ca 2+ , or when the Ca 2+ -channel blocker Verapamil was present, no swelling was observed. However, ACh also induced swelling when Ca 2+ was replaced by 0.5 mM K + or Na + . The Ca 2+ -dependent swelling was, in all cases, inhibited by guanosine-5′-O-(2-thiodiphosphate) (GDP-β-S), indicating the involvement of a G-protein. The K + /Na + -dependent ACh-induced swelling was not inhibited by GDP-β-S. These results suggest that all of the hormones tested have receptors present on the plasma membrane of etiolated wheat protoplasts, which can activate a G-protein.