Studies on H+-Translocating ATPases in Plants of Varying Resistance to Salinity 1: II. K+ Strongly Promotes Development of Membrane Potential in Vesicles from Cotton Roots

摘要

Mg2+-ATP-dependent H+-translocation has been studied in membrane vesicles derived from the roots of Gossypium hirsutum L. var. Acala San Jose 2. Establishment of a positive membrane potential was followed by measuring SCN− accumulation; establishment of ΔpH across the vesicle membranes by measuring quinacrine fluorescence quenching. High specificity for ATP was shown, and H+-translocation was oligomycin stable. The pH profile for H+-translocation showed an optimum at 5.5. The relationship between SCN− accumulation and ATP concentration was approximately Michaelian; the apparent Km was 0.7 millimolar. K-2-(N-morpholino)ethanesulfonic acid strongly promoted ATP-dependent SCN− uptake (up to 180% stimulation). The effect was not given by Na-Mes. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone totally inhibited SCN− accumulation, both in the presence and absence of K-2(N-morpholino)ethanesulfonic acid. Vanadate at 200 micromolar inhibited SCN− uptake by about 10 to 40% in the absence of K+, but more strongly in its presence (about 60%). NO3− at 100 millimolar inhibited initial rate of quinacrine quenching by about 25%. The NO3− insensitive fraction was activated by K+; and inhibited by 200 micromolar vanadate to about 40%, provided K+ was present. Saline conditions during the growth of the plants had no appreciable effect on the observed characteristics of H+-translocation.