Until recently the role of cyclic nucleotide monophosphates (cNMPs) in plants had been controversial, with equivocal data about their concentrations, biosynthetic and degrading enzymes, and cellular targets. This review discusses the current knowledge in this field, with focus on the largest class of cNMP targets in plant cells, the cyclic nucleotide-gated channels (CNGCs). Aspects of structure and function are addressed, with reference to studies in heterologous systems and in planta. The picture emerging, albeit still fragmented, is of proteins with diverse functions in the control of ion homeostasis, development, and defense against biotic and abiotic threats.
Isolated membrane vesicles from the obligately acidophilic bacterium Bacillus acidocaldarius generated an electrochemical gradient of protons (APLH+) upon energization with ascorbate-phenazine methosulfate at pH 6.0 or 3.0. At pH 6.0, there was little or no transmembrane pH gradient (ApH), but a transmembrane electrical potential (A*) of ca.-77 mV, positive out, was observed. At pH 3.0, a ApH equivalent to-100 mV, acid out, and a A* of-73 mV, positive out, were observed upon energization. The total magnitude of the AILH+ was higher than that of whole cells at acid pH, but the very large ApHs and the reversed A*s, i.e., inside positive, that are typical of acidophile cells were not observed in the vesicles. The vesicles exhibited energy-dependent accumulation of a-aminoisobutyric acid that was inhibited by both nigericin and valinomycin (plus K+) at pH 3.0 but was inhibited little by nigericin at pH 6.0.
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