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

Body weight reducing effect of oral boric acid intake

BACKGROUND

Boric acid is widely used in biology, but its body weight reducing effect is not researched.

METHODS

Twenty mice were divided into two equal groups. Control group mice drank standard tap water, but study group mice drank 0.28mg/250ml boric acid added tap water over five days. Total body weight changes, major organ histopathology, blood biochemistry, urine and feces analyses were compared.

RESULTS

Study group mice lost body weight mean 28.1% but in control group no weight loss and also weight gained mean 0.09% (p<0.001). Total drinking water and urine outputs were not statistically different. Cholesterol, LDL, AST, ALT, LDH, amylase and urobilinogen levels were statistically significantly high in the study group. Other variables were not statistically different. No histopathologic differences were detected in evaluations of all resected major organs.

CONCLUSION

Low dose oral boric acid intake cause serious body weight reduction. Blood and urine analyses support high glucose, lipid and middle protein catabolisms, but the mechanism is unclear.

Rapid determination of seed vigor based on the level of superoxide generation during early imbibition

It has been reported that a large amount of reactive oxygen species (ROS) is produced during seed imbibition and this ROS is related to seed vigor. To make this physiological mechanism clear, we have used 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo(1,2-alpha)pyrazin-3-one (MCLA) as a sensitive and physiologically compatible probe for the determination of superoxide anion (O(2)(*-)) production in vivo. Our results showed that dry rice (Oryzae sativa L.) seed embryo cells possessed the capacity to generate O(2)(*-). Conversely, the O(2)(*-) production of seed embryo cells was inhibited by quinacrine (QA) and diphenylene iodonium (DPI), two specific inhibitors of NADPH oxidase, and O(2)(*-) induced MCLA-mediated chemiluminescence was also blocked by superoxide dismutase (SOD). Additionally, O(2)(*-) -production ability increased dramatically in a NADPH-dependent way in the plasma membrane protein abstract from rice seed embryo cells, whereas SOD and the inhibitors mentioned above suppressed O(2)(*-) production. These preliminary results suggested that rice seeds contained intrinsic NADPH oxidase activity. To validate this conclusion, dichlorofluorescein (DCF) fluorescence staining was used (observed under a laser scanning microscope, LSM) to reflect the in situ assessment of O(2)(*-) -generation. The position of O(2)(*-) production located at the plasma membrane. Additionally the ability to synthesize O(2)(*-) was activated directly by calcium ions. These observations are in accord with the character of NADPH oxidase catalyzed O(2)(*-) -generation. All these results indicated that NADPH oxidase contribute to O(2)(*-) production and release to the outside. We concluded that NADPH oxidase plays an intrinsic role as an NADPH sensor, so, measuring the O(2)(*-) one can monitor the NADPH concentration, which is an index of seed vigor. Therefore the O(2)(*-) generation during early imbibition can serve as a rapid measurement of seed vigor.

The effect of auxins (IAA and 4-Cl-IAA) on the redox activity and medium pH of Zea mays L. root segments

Indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA) were tested at different concentrations and times for their capacity to change the redox activity and medium pH of maize root segments. The dose-response surfaces (dose-response curves as a function of time) plotted for redox activity and changes in medium pH (expressed as DeltapH) had a similar shape for both auxins, but differed significantly at the optimal concentrations. With 4-Cl-IAA, the maximal values of redox activity and medium pH changes were observed at 10(-10) M, which was a 100-fold lower concentration than with IAA. Correlations were observed between redox activity and medium pH changes at the optimal concentrations of both IAA and 4-Cl-IAA. The results are discussed herein, taking into account both the concentration of the auxins and the effects produced by them.

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

Pollen exposure induces allergic airway inflammation in sensitized subjects. The role of antigenic pollen proteins in the induction of allergic airway inflammation is well characterized, but the contribution of other constituents in pollen grains to this process is unknown. Here we show that pollen grains and their extracts contain intrinsic NADPH oxidases. The pollen NADPH oxidases rapidly increased the levels of ROS in lung epithelium as well as the amount of oxidized glutathione (GSSG) and 4-hydroxynonenal (4-HNE) in airway-lining fluid. These oxidases, as well as products of oxidative stress (such as GSSG and 4-HNE) generated by these enzymes, induced neutrophil recruitment to the airways independent of the adaptive immune response. Removal of pollen NADPH oxidase activity from the challenge material reduced antigen-induced allergic airway inflammation, the number of mucin-containing cells in airway epithelium, and antigen-specific IgE levels in sensitized mice. Furthermore, challenge with Amb a 1, the major antigen in ragweed pollen extract that does not possess NADPH oxidase activity, induced low-grade allergic airway inflammation. Addition of GSSG or 4-HNE to Amb a 1 challenge material boosted allergic airway inflammation. We propose that oxidative stress generated by pollen NADPH oxidases (signal 1) augments allergic airway inflammation induced by pollen antigen (signal 2).

Triton X-100 inhibition of yeast plasma membrane associated NADH-dependent redox activities

Plasma membrane (PM) vesicles isolated from the yeast Saccharomyces cerevisiae (wild-type NCIM 3078, and a MG 21290 mutant pma 1-1) were used to monitor the effect of the detergents, 3-[(3-cholamidopropyl) dimethylammonio]-1-propane sulfonate (Chaps) and Triton X-100, on (H+)-ATPase (E.C. 3.6.1.35), NADH oxidase and NADH-hexacynoferrate (III)[HCF (III)] oxidoreductase (E.C. 1.6.99.3) activities. The results obtained show that Triton X-100 inhibited both membrane bound and solubilized NADH-dependent redox activities. The nature of this inhibition as determined for NADH-HCF(III) oxidoreductase was non-competitive and the Ki values for wild and mutant enzymes were 1.2 x 10(-5) M and 8.0 x 10(-6) M, respectively. The findings are interpreted, in view of the established reports, that the active site architecture of PM bound NADH-dependent oxidoreductase in yeast is likely to be different than in other eukaryotes.

Ability of different biomaterials to enantioselectively catalyze oxidation and reduction reactions

We studied the ability of different biomaterials to enantioselectively catalyze oxidation or reduction reactions with the help of substrate rac-1-m or p-ArCH(OH)Me and the 1-o-ArC(O)Me derivatives. Apoenzyme (NAD(P)(+)-dependent secondary alcohol dehydrogenase(NAD(P)-E)) and cofactor (NAD(P)(+)) were activated by preincubating immobilized aqueous plant leaf (e.g., young wheat leaves), cereal tissue (wheat bran), vegetable (e.g., carrot), and seaweed (e.g., wakame seaweed) solutions, and the NAD(P)-E oxidized only (R)-isomers highly enantioselectively. Thus, greater than 99% ee(s) of (S)-isomers (1m-5m and 1p-5p) can be obtained from corresponding rac-1-m or p-ArCH(OH)Me. Further, immobilized chlorella cells and immobilized baker's yeast can reduce highly stereoselectively; greater than 99% ee(s) of (S)-isomers (1o-5o) can be obtained from corresponding 1-o-ArC(O)Me. Specific use of each isomer ((S)-6 and (R)-6) with greater than 99% ee(s) of racemic-1-2-NpCH(OH)Me becomes possible through selective use of NAD(P)-E eluted from artemisia vulgaris indica leaves and young wheat leaves. We suggest that the pH of the reaction media can determine not only the direction of NAD(P)-E, toward enantioselectively catalyzed oxidation (pH > 7.0) or reduction reaction (pH < 7.0), but also the regioselective reactivity of NAD(P)-E to the substrate o- (pH < 7.0), m-, and p-substituted groups (pH > 7.0). Thus, in comparison to current biocatalysts, several biomaterials can serve as asymmetric reagent bases, providing easily obtained, low-cost natural catalysts with stereoselectivity, regioselectivity, and substrate specificity that work under mild conditions for asymmetric synthesis of organic compounds.

Apparent absence of a redox requirement for blue light activation of pump current in broad bean guard cells

In guard cells, membrane hyperpolarization in response to a blue light (BL) stimulus is achieved by the activation of a plasma membrane H(+)-ATPase. Using the patch clamp technique on broad bean (Vicia faba) guard cells we demonstrate that both steady-state- and BL-induced pump currents require ATP and are blocked by vanadate perfused into the guard cell during patch clamp recording. Background-pump current and BL-activated currents are voltage independent over a wide range of membrane potentials. During BL-activated responses significant hyperpolarization is achieved that is sufficient to promote K(+) uptake. BL activation of pump current becomes desensitized by three or four pulses of 30 s x 100 micromol m(-2) s(-1) BL. This desensitization is not a result of pump inhibition as maximal responses to fusicoccin are observed after full BL desensitization. BL treatments prior to whole cell recording show that BL desensitization is not due to washout of a secondary messenger by whole cell perfusion, but appears to be an important feature of the BL-stimulated pump response. We found no evidence for an electrogenic BL-stimulated redox chain in the plasma membrane of guard cells as no steady-state- or BL-activated currents are detected with NADH or NADPH added to the cytosol in the absence of ATP. Steady-state- nor BL-activated currents are affected by the inclusion along with ATP of 1 mM NADH in the pipette under saturating red light or by including NADPH in the pipette under darkness or saturating red light. These data suggest that reduced products of photosynthesis do not significantly modulate plasma membrane pump currents and are unlikely to be critical regulators in BL-stimulation of the plasma membrane H(+)-ATPase in guard cells.

In vivo and in vitro effects of boron and boronated compounds

Boron is ubiquitously present in soils and water. Associated with pectin it is essential for vascular plants as a component of cell walls, and it stabilizes cell membranes. It is required for the growth of pollen tubes and is involved in membrane transport, stimulating H(+)-pumping ATPase activity and K+ uptake. However, a high boron concentration in the soils is toxic to plants and some boronated derivatives are used as herbicides. An absolute requirement for boron has not been definitively demonstrated in animals and humans. However, experiments with boron supplementation or deprivation show that boron is involved in calcium and bone metabolism, and its effects are more marked when other nutrients (cholecalciferol, magnesium) are deficient. Boron supplementation increases the serum concentration of 17 beta-estradiol and testosterone but boron excess has toxic effects on reproductive function. Boron may be involved in cerebral function via its effects on the transport across membranes. It affects the synthesis of the extracellular matrix and is beneficial in wound healing. Usual dietary boron consumption in humans is 1-2 mg/day for adults. As boron has been shown to have biological activity, research into the chemistry of boronated compounds has increased. Boronated compounds have been shown to be potent anti-osteoporotic, anti-inflammatory, hypolipemic, anti-coagulant and anti-neoplastic agents both in vitro and in vivo in animals.

Regulation of enzymatic activity: one possible role of dietary boron in higher animals and humans

It is well established that vascular plants, diatoms, and some species of marine algal flagellates have acquired an absolute requirement for boron (B), although the primary role remains unknown. Discovery of naturally occurring organoboron compounds, all ionophoric macrodiolide antibiotics with a single B atom critical for activity, established at least one biochemical role of B. The unusual nature of B chemistry suggests the possibility of a variety of biological roles for B. At physiological concentrations and pH, B may react with one N group or one to four hydroxyl groups on specific biological ligands with suitable configuration and charge to form dissociable organoboron compounds or complexes. Suitable ligands include pyridine (e.g., NAD+ or NADP) or flavin (e.g., FAD) nucleotides and serine proteases (SP). B reacts with the cis adjacent hydroxyls on the ribosyl moiety of the nucleotides or, in the serine proteases, the N on the imidazole group of histidine or the hydroxyl group on the serine moiety. Reversible inhibition by B of activity of SP or oxidoreductases that require pyridine or flavin nucleotides is well known. Therefore, a proposed essential role for B is as a regulator of relevant pathways, including respiratory burst, that utilize these enzymes.

Oxidoreductases in plant plasma membranes

Electron transporting oxidoreductases at biological membranes mediate several physiological processes. While such activities are well known and widely accepted as physiologically significant for other biological membranes, oxidoreductase activities found at the plasma membrane of plants are still being neglected. The ubiquity of the oxidoreductases in the plasma membrane suggests that the activity observed is of major importance in fact up to now no plant without redox activity at the plasmalemma is known. Involvement in proton pumping, membrane energization, ion channel regulation, iron reduction, nutrient uptake, signal transduction, and growth regulation has been proposed. However, positive proof for one of the numerous theories about the physiological function of the system is still missing. Evidence for an involvement in signalling and regulation of growth and transport activities at the plasma membrane is strong, but the high activity of the system displayed in some experiments also suggests function in defense against pathogens.

Electron and proton transport across the plasma membrane

Transplasm membrane electron transport in both plant and animal cells activates proton release. The nature and components of the electron transport system and the mechanism by which proton release is activated remains to be discovered. Reduced pyridine nucleotides are substrates for the plasma membrane dehydrogenases. Both plant and animal membranes have unusual cyanide-insensitive oxidases so oxygen can be the natural electron acceptor. Natural ferric chelates or ferric transferrin can also act as electron acceptors. Artificial, impermeable oxidants such as ferricyanide are used to probe the activity. Since plasma membranes contain b cytochromes, flavin, iron, and quinones, components for electron transport are present but their participation, except for quinone, has not been demonstrated. Stimulation of electron transport with impermeable oxidants and hormones activates proton release from cells. In plants the electron transport and proton release is stimulated by red or blue light. Inhibitors of electron transport, such as certain antitumor drugs, inhibit proton release. With animal cells the high ratio of protons released to electrons transferred, stimulation of proton release by sodium ions, and inhibition by amilorides indicates that electron transport activates the Na+/H+ antiport. In plants part of the proton release can be achieved by activation of the H+ ATPase. A contribution to proton transfer by protonated electron carriers in the membrane has not been eliminated. In some cells transmembrane electron transport has been shown to cause cytoplasmic pH changes or to stimulate protein kinases which may be the basis for activation of proton channels in the membrane. The redox-induced proton release causes internal and external pH changes which can be related to stimulation of animal and plant cell growth by external, impermeable oxidants or by oxygen.