Development of Fe-deficiency responses in cucumber (Cucumis sativus L.) roots: involvement of plasma membrane H(+)-ATPase activity.
One of the mechanisms through which some strategy I plants respond to Fe-deficiency is an enhanced acidification of the rhizosphere due to proton extrusion. It was previously demonstrated that under Fe-deficiency, a strong increase in the H(+)-ATPase activity of plasma membrane (PM) vesicles isolated from cucumber roots occurred. This result was confirmed in the present work and supported by measurement of ATP-dependent proton pumping in inside-out plasma membrane vesicles. There was also an attempt to clarify the regulatory mechanism(s) which lead to the activation of the H(+)-ATPase under Fe-deficiency conditions. Plasma membrane proteins from Fe-deficient roots submitted to immunoblotting using polyclonal antibodies showed an increased level in the 100 kDa polypeptide. When the plasma membrane proteins were treated with trypsin a 90 kDa band appeared. This effect was accompanied by an increase in the enzyme activity, both in the Fe-deficient and in the Fe-sufficient extracts. These results suggest that the increase in the plasma membrane H(+)-ATPase activity seen under Fe-deficiency is due, at least in part, to an increased steady-state level of the 100 kDa polypeptide.
Dipartimento di Produzione Vegetale, University of Milan, Italy.
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D000255:Adenosine Triphosphate / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D018553:Cucumis sativus / Q000378:metabolism / Q000502:physiology*; D038181:FMN Reductase; D006868:Hydrolysis; D015151:Immunoblotting; D000090463:Iron Deficiencies; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology*; D017494:Proton Pumps / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism*
D017494:Proton Pumps; D000255:Adenosine Triphosphate; D038181:FMN Reductase; D009247:NADH, NADPH Oxidoreductases; C023903:ferric citrate iron reductase; D006180:Proton-Translocating ATPases