The possible role of redox-associated protons in growth of plant cells

Abstract

The protons excreted by plant cells may arise by two different mechanisms: (1) by the action of the plasma membrane H(+)-ATPase and (2) by plasma membrane redox reactions. The exact proportion from each source is not known, but the plasma membrane H(+)-ATPase is, by far, the major contributor to proton efflux. There is still some questions of whether the redox-associated protons produced by NADH oxidation on the inner side of the plasma membrane traverse the membrane in a 1:1 relationship with electrons generated in the redox reactions. Membrane depolarization observed in the presence of ferricyanide reduction by plasma membranes of whole cells or tissues or the lag period between ferricyanide reduction and medium acidification argue that only scalar protons may be involved. The other major argument against tight coupling between protons and electrons involves the concept of strong charge compensation. When ferricyanide is reduced to ferrocyanide on the outside of cells or tissues, an extra negative charge arises, which is compensated for by the release of H+ or K+, so that the total ratio of increased H+ plus K+ equals the electrons transferred by transmembrane electron transport. These are strong arguments against a tight coupling between electrons and protons excreted by the plasma membrane. On the other hand, there is no question that inhibitor studies provide evidence for two mechanisms of proton generation by plasma membranes. When the H(+)-ATPase activity is totally inhibited, the addition of ferricyanide induces a burst of extra proton excretion, or vice versa, when plasma membrane redox reactions are inhibited, the H(+)-ATPase can function normally. Since plasma membrane redox reactions and associated H+ excretion are related to growth it is possible that in plants the ATPase-generated protons have a different function from redox-associated protons. The H(+)-ATPase-generated protons have been considered for many years to be necessary for cell wall expansion, allowing elongation to take place. A special function of the redox-generated protons may be in initiating proliferative cell growth, based on the presence of a hormone-stimulated NADH oxidase in membranes of soybean hypocotyls and stimulation of root growth by low concentrations of oxidants. Here we propose that this NADH oxidase and the redox protons released by its action control growth. The mechanism for this may be the evolution of protons into a special membrane domain, from which a signal to initiate cell proliferation may originate, independent of the action of the H(+)-ATPase-generated protons.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of osmotic shock on the redox system in plasma membrane of Dunaliella salina

“…salina is very sensitive to osmotic shock. Except of slight hyperosmtic shock, abrupt hyperosmotic shock and hypoosmotic shock greatly decreased the rates of NADH oxidation and Fe(CN) 6 3-reduction (Tab 1), which is in accordance with the phenomenon observed by Crane and Barr under salt stress [3] and Qiu et al under water stress [4]. The electron transport chains of plasmalemma redox system are multiple [11,12 ]: innerside or outerside cis-plasmalemma electron transfer; inward or outward transplasmalemma electron transfer etc.…”

“…This process is very important in the reaction and adaptation of plants to various environmental stress, such as pathogen, drought, low temperature, hypoosmotic shock and UV radiation. Barr and Crane [3] found that the redox system in the plasmalemma of carrot cells was very sensitive to salt stress, both NADH oxidation, Fe(CN) 6 3-reduction and H + extrusion were inhibited. Qiu et al [4] also demonstrated that the redox activities in the plasmalemma of wheat root cells were greatly decreased under water stress.…”

ROS generated by pollen NADPH oxidase provide a signal that augments antigen-induced allergic airway inflammation

“…different plant species contain oxidases that generate ROS and regulate vital physiological functions such as seed germination and root hair growth (32,33). We reasoned by analogy that pollen germination is likely to require ROS generated by these oxidases during pollination processes.…”

Proposed Physiologic Functions of Boron in Plants Pertinent to Animal and Human Metabolism

“…Other evidence indicates that the effects of boron on membrane function may be associated more directly with proton pumping or changes in a redox system in the plasmalemma. Both the hyperpolarization of the membrane potential (in sunflower roots) and the stimulation of the ferricyanide reduction (in carrot cells) could be related to the activity of NADH oxidase, an enzyme that could provide protons for export (15,16). In 1991, Barr and Crane (17) reported that the activity of plasmalemma NADH oxidase was stimulated by boron.…”