Repression of asolectin-dependent activation of partially lipid depleted ATPase prepared from the plasma membrane-enriched fraction of cucumber roots due to Ca2+ starvation

Matsumoto, H.; Chung, G.C.

Plant and Cell Physiology 29(8): 1279-1287


ISSN/ISBN: 0032-0781
DOI: 10.1093/oxfordjournals.pcp.a077636
Accession: 001932046

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In cucumber plants grown in solution culture, the ATPase activity of the plasma membrane-enriched fraction was severely inhibited when Ca2+ was withdrawn from the medium for 5 days, although the root system was apparently unaffected. Partially lipid-depleted ATPases with similar ratios of phospholipid to protein were prepared from the plasma membrane-enriched fraction of roots of plants grown with and without Ca2+ supply, and their properties compared. SDS-PAGE showed that the polypeptide components in the control and the Ca2+-starved roots were similar. Partially lipid-depleted ATPase reassociated with asolectin, the lecithin from soybean, showed typical characteristics of plasma membrane type ATPase: pH optimum at 6.5, high specificity for ATP as the substrate and strong inhibition by vanadate but not nitrate. The activity of reassociated ATPase obtained from the control roots was apparently higher than the activity obtained from Ca2+-starved roots. The amount of asolectin required for maximum activation of the partially lipid-depleted ATPase prepared from control roots was much lower than that prepared from Ca2+-starved roots. Reassociation of partially lipid-depleted ATPase with asolectin produced higher ATPase activity than that with individual phospholipids. The activation of partially lipid-depleted ATPase prepared from control roots with asolectin was not inhibited by the addition of a sample prepared from Ca2+-starved roots. Thus, a decrease in the functional association of ATPase with phospholipids might be one of the physiological injuries in root cell membranes of cucumber caused by Ca2+ starvation.