Repression of asolectin dependent activation of partially lipid depleted atpase prepared from the plasma membrane enriched fraction of cucumber roots due to calcium starvation
Matsumoto, H.; Chung, G.C.
Plant and Cell Physiology 29(8): 1279-1288
ISSN/ISBN: 0032-0781 Accession: 007746526
The ATPase activity of the plasma membrane-enriched fraction was severely inhibited by withdrawal of Ca2+ from the medium for 5 days, although the root system appeared to be unaffected to visual inspection. Partially lipid-depleted ATPases with similar ratios of phospholipid to protein were prepared from the plasma membrane-enriched fraction of cucumber [Cucumis sativus] roots cultured with control medium and one lacking Ca2+, and their properties were compared. SDS disc polyacrylamide gel electrophoresis showed that the polypeptide components were essentially similar between control and Ca2+-starved roots. 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 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 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.