Excessive low-affinity Na؉ uptake is toxic to the growth of glycophytic plants. Recently

Two cDNA clones encoding 14-3-3 homologous proteins were isolated from Vicia faba. Deduced amino acid sequences share different degrees of homology with other plant 14-3-3 proteins. Both clones, under the control of the CaMV 35S promoter, were transformed into tobacco plants. Immunoblotting showed three different forms of ca. 31, 34, and 37 kDa, indicating a covalent modification of the expressed 14-3-3 proteins. These forms were mainly present in the microsomal fraction. Patch-clamp studies of mesophyll protoplasts of the transformants revealed a strongly enhanced K + conductance compared to the wild type. This indicates the involvement of 14-3-3 proteins in ion channel regulation, presumably by modulating kinase activities or binding the channel.

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The activities of the major ion pathways in the plasma membranes of plants are sensitive to the membrane voltage, V. Therefore, these 'electroenzymes' interact with each other via the free running voltage under physiological conditions. A physical background is given here, of how to calculate these interactions on the basis of experimental data on these electroenzymes. Simplifying model calculations with five major electroenzymes from plant cells (H(+) pump, inward and outward rectifying channels for K(+), a Cl(-) channel, and a 2H(+)/Cl(-) symporter) show that osmotic relations are balanced in the long-term not by an appropriate steady-state, but by alternation between a state of salt uptake at V < < E(K) (the Nernst equilibrium voltage for K(+) diffusion) and a state of salt loss at V > E(K). Several specific properties of the model are discussed numerically, e.g. minimum configuration for oscillations (with two electroenzymes), temperature-compensation, the physiological impact of fast gating in plant membranes, and solution of possible paradoxes, such as flux stimulation by conductance inhibition.