PLANT PHYSIOLOGY , Vol 114, Issue 3 857-862, Copyright © 1997 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Changes in the Level and Activation State of the Plasma Membrane H+-ATPase during Aging of Red Beet Slices
R. Papini and M. I. De Michelis
Istituto di Botanica, Universita di Genova, Corso Dogali 1c, 16136 Genoa, Italy
The effect of aging on the plasma membrane (PM) H+-ATPase of red beet (Beta
vulgaris L.) parenchyma discs was analyzed in PM purified by aqueous
two-phase partitioning. Aging increased both the activity and the amount of
immunodetectable H+-ATPase in the PM. The activity assayed at slightly
alkaline pH values increased earlier and more strongly than that assayed at
acidic pH values, so that the pH curve of the enzyme from aged beet discs
was shifted toward more alkaline values. Aging decreased the stimulation of
the PM H+-ATPase activity by controlled trypsin treatments or by
lysophosphatidylcholine. After trypsin treatment the pH dependence of
H+-ATPase from dormant or aged beet discs became equal. These results
indicate that aging not only increases the level of H+-ATPase in the PM,
but also determines its activation, most likely by modifying the
interaction between the autoinhibitory carboxyl-terminal domain and the
catalytic site. When the PM H+-ATPase activity was assayed at a slightly
alkaline pH, the tyrosine modifier N-acetylimidazole inhibited the
H+-ATPase in the PM from dormant beet discs much less than in the PM from
aged discs, suggesting that modification of a tyrosine residue may be
involved in the activation of the PM H+-ATPase induced by aging. The
results are discussed with regard to aging-induced development of
transmembrane transport activities.
