ISSN:
1432-2048
Keywords:
Auxin
;
Coleoptile
;
Fusicoccin
;
H+-ATPase activity
;
Zea (H+-ATPase)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In vivo treatment of maize (Zea mays L.) coleoptile segments with auxin (indole-3-acetic acid; IAA) and fusicoccin (FC) followed by plasma-membrane isolation was used to characterize the effects of these treatments on the plasma-membrane H+-ATPase. Both IAA and FC increased H+ extrusion and elongation rate of the coleoptile segments, FC more strongly than IAA. Plasma membranes isolated after in-vivo treatment with FC showed a twofold stimulation of ATP hydrolysis and a several-fold stimulation of H+ pumping, whereas no effect was observed after IAA treatment, irrespective of whether the plasma membranes were prepared by two-phase partitioning or sucrose-gradient centrifugation. A more detailed investigation of the kinetic properties and pH dependence of the enzyme showed that FC treatment led to a twofold increase in V max, a decrease in K m for ATP from 1.5 mM to 0.24 mM, and a change in pH dependence resulting in increased activity at physiological pH levels. Again, IAA treatment showed no effects. Quantitation of the H+-ATPase by immunostaining using four different antibodies revealed no difference between IAA-and FC-treated material, and controls. From these data we conclude that (i) neither IAA nor FC gives rise to an increase in the amount of H+ -ATPase molecules in the plasma membrane that can be detected after membrane isolation, and (ii) if the H+-ATPase is activated by IAA, this activation is, in contrast to FC activation, not detectable after membrane isolation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00195727
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