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The modulating effects of pH and benzyladenine on the Ca 2+ – and Mg 2+ ‐ATPases in the plasmalemma of wheat root cells
Author(s) -
Kuiper Daan,
Sommarin Marianne,
Kylin Anders
Publication year - 1992
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1992.tb04677.x
Subject(s) - atpase , membrane , chemistry , substrate (aquarium) , cytokinin , plant cell , biochemistry , plant physiology , biophysics , enzyme , botany , biology , auxin , ecology , gene
Plant cells frequently and rapidly have to respond to environmental changes for survival. Regulation of transport and other energy‐requiring processes in the plasmalemma of root cells is therefore one important aspect of the ecological adaptation of plants. Wheat ( Triticum aestivum L. cv. Drabant) was grown hydroponically, with or without 50 n M benzyladenine in the medium, and plasma membranes from root cells of 8‐day‐old plants were prepared by aqueous polymer two‐phase partitioning. The influence of Ca 2+ and Mg 2+ on the plasmalemma ATPase activities was investigated. The presence of benzyladenine during growth increased the ATPase activity, that dependent upon Ca 2+ more than that elicited by Mg 2+ . As a general characteristic, ATP was the preferred substrate, but all nucleotide tri‐ and diphosphates could be accepted with activities in plasma membranes from control plants of 7‐36% (Mg 2+ ) and 40‐86% (Ca 2+ ) and in plasma membranes from benzyladenine‐treated plants of 12‐47% (Mg 2+ ) and 53‐102% (Ca 2+ ) as compared with activities obtained with ATP. Nucleotidemonophosphates were not hydrolyzed by the preparations. In preparations from benzyladenine‐treated plants one peak of Ca 2+ ‐ATPase at pH 5.2–5.6, with a tail from pH 6 and upwards, and one peak of Mg 2+ ‐ATPase at pH 6.0–6.5 were observed in the presence of EDTA in the assay media. In preparations from control plants, the addition of EDTA to the assays resulted in a wide optimum between pH 6 and 7 for Mg 2+ ‐ATPase and low Ca 2+ ‐ATPase activity with no influence of pH in the range 4.5 to 8. Analysis of the pH dependence in the presence of both Ca 2+ and Mg 2+ indicates that the control plants mainly contain Mg 2+ ‐ATPase corresponding to the proton pump. Preparations from benzyladenine‐treated wheat roots show, in addition, activation by Ca 2+ , which, in the slightly alkaline pH range may correspond to a Ca 2+ ‐extruding (Ca 2+ + Mg 2+ )‐ATPase. In the acidic range, the responses are more complicated: the Mg 2+ ‐ATPase is inhibited by vanadate, while the Ca 2+ ‐ATPase is insensitive, and benzyladenine added during growth influences the interaction between Ca 2+ and Mg 2+ in a way that parallels the effect of high salt medium.