Membrane Potentials of Vallisneria Leaf Cells and Their Relation to Photosynthesis

Abstract

A study has been made of the effects of the inhibitors carbonylcyanide n-chlorophenylhydrazone (CCCP), 3-(3,4-dichkophenyl)-1,14dnethyl urea (DCMU), and of anoxia on the lgt-sensitive membrane potential of VaNsneria leaf cells. The present results are compared with the known effects of these inbibitors on ion transport and photosynthesis (Prins 1974 Ph.D thesis). The membrane potential is composed of a diffusion potential plus an electrogenic component. The electrogenic potential is about -13 millivolts in the dark and -80 millivolts in the light. The inhibitory effect of DCMU and CCCP on the electrogenic mechanisms strongly depends on the light intensity used, the inhibition being less at a higher Light intensity. This is of significance in view of the often conflicting results obtained with these inhibitors. With The present results show that the sensitivity of the membrane potential to inhibitors depends very much on the light intensity used. The meaning of this will be discussed. For Nitella it has been shown that the more negative potential in the light is caused by an electrogenic pump (19,20). Generally, it is assumed that this electrogenic pump is a proton extrusion pump; this may be true for Vallisneria also. MATERIALS AND METHODSPlants of V. spiralis were grown aquatically in a plastic tank on a slightly alkaline soil at room temperature (about 20 C).Leaf strips of 20 x 4 mm were mounted in a modified Mertz chamber (12), except for experiments on the effect of 02, in which small (2-mm) leaf strips were used from the margins of the leaves which are devoid of gas-filled intercellar spaces. By doing this a more rapid exchange of 02 between the cells and the medium was obtained. Cells of the epidermis or outer layer of mesophyll were used. Membrane potentials were measured using 3 M KCl-filled glass microelectrodes. The cells were too small to use the classic two-electrode method for membrane resistance measurements, therefore electrical resistances were measured with the single electrode method of Anderson et al. (1), using 10-kHz current pulses between +5 and -5 namp. Over this range the resistance was ohmic and no rectification was observed. Resistances lower than 1.5 Mgl could not be measured accurately with the set-up used.Despite the recent criticism on this method (6)

The Proton Electrochemical Transmembrane Gradients Generated by the Transfer Cells of the Haustorium of Polytrichum formosum and Their Use in the Uptake of Amino Acids

“…2 and 3 of reference 3). In Vallisneria spiralis, an aquatic angiosperm, the PD of the epidermal transfer cells is similar to that of the leaf parenchyma cells (27). In various species, and more particularly in Capsicum annuum, Fe deficiency leads to a stimulation of H+ excretion by the roots and to a concomittant increase of malate and citrate synthesis.…”

“…Indeed, we were interested in determining whether this cell type not only increases the surface of exchange between the apoplast and the symplast but also generates electrochemical potential gradients different from those of the parenchyma cells or from those of the cells from which its originates. As emphasized in the discussion, the data presently available (3,16,21,27) do not provide a clear answer to this question. The other aim of this paper is to examine whether the electrochemical potential gradients generated by the transfer cells of the haustorium are used indeed to achieve active uptake of the organic solutes present in the apoplast of the gametophytes, as it was suggested by our previous results (6,7), and then to bring information on the properties of exchanges between the two generations.…”

Photosynthesis Activates Plasma Membrane H+-ATPase via Sugar Accumulation

“…Photosynthesis regulates ion transport across the plasma membrane (Spanswick, 1981;Marten et al, 2010). Light-induced hyperpolarization of the plasma membrane has been particularly well studied in a diversity of plants, including Chara corallina and Vallisneria spiralis (Prins et al, 1980;Mimura and Tazawa, 1986). Photosynthesis-dependent membrane hyperpolarization is believed to result from activation of the plasma membrane H + -ATPase.…”

Light-Induced Polar pH Changes in Leaves of Elodea canadensis

“…Although the effect of DMO supports the hypothesis that the polarity was influenced by acidification of the cytoplasm, acetic acid, which normally invokes the same reaction as DMO, did not suppress, but rather stimulated, the pH polarity. In Vallisneria spiralis, also a submerged aquatic member ofthe Hydrocharitaceae, acetate stimulated the lightdependent proton pump as judged from the hyperpolarization of the membrane potential (18). From these considerations, we conclude that the stimulating effect of light and the inhibiting effect of CO2 (DIC) are not caused by a change in cytoplasmic pH.…”

“…These polar reactions are thought to be associated with the ability of these species to use bicarbonate as a carbon source for photosynthesis. The acidification of the medium on the lower side of the leaf is due to an active proton efflux while the release of hydroxyl ions on the upper side of the leaf is a passive process (18). The polar reaction facilitates the use of bicarbonate in photosynthesis by shifting the bicarbonate-CO2 equilibrium in the unstirred layer on the lower side of the leaf, thereby increasing the CO2 concentration of the unstirred layer and increasing diffusion ofCO2 into the leaf (19)(20)(21)(22).…”