Developmental Changes in the NAD Content in Sugar-Beet Root Mitochondria and Their Effect on the Oxidative Activity of These Organelles

The NAD content was determined in mitochondria isolated from sugar-beet roots at various stages of plant development. A high NAD content (7.6 ± 0.9 nmol/mg mitochondrial protein) was observed in the mitochondria of actively growing roots of 80–95-day-old plants, but it decreased ca. twofold by the end of the first year of plant development, before the roots were harvested for storage. The mitochondria isolated from roots stored at low temperature for two to three months and those after five to eight days of regrowth during the second year of plant development manifested an even lower NAD content (2.2 ± 0.4 and 2.0 ± 0.5 nmol/mg protein, respectively). A drastic decrease in the NAD content in mitochondria from stored roots did not result from the impairment of the inner membrane of these organelles and was evidently regulatory in its nature. The effect of developmental changes in the intramitochondrial NAD content on the malate oxidation pattern was studied. In the mitochondria of stored roots, the low NAD content limited the rate of malate oxidation in state 3, because the addition to the reaction mixture of exogenous NAD, which can be transported to the mitochondrial matrix, promoted malate oxidation by 30–50%. Rotenone inhibited malate oxidation in the stored-root mitochondria by more than 70%; in this case, the rate of rotenone-resistant malate oxidation in these organelles increased by several times in the presence of exogenous NAD. In the mitochondria of the growing root, exo-genous NAD did not affect the rate of malate oxidation, and rotenone inhibited it only by 25–35%. The analysis of the data obtained here and the published evidence suggests the existence of a universal mechanism of respiration control and the regulation of the functional activity of plant mitochondria. This mechanism acts through a change in the NAD content in the organelle matrix. This NAD can be used in the course of plant development, e.g., during the transition of sugar-beet-root cells in the dormant state, when the respiration rate must decline.     

Effect of salicylic acid on the alternative pathway of yellow lupine respiration

The effects of salicylic acid (SA) on the rate of respiration and the activity of cyanide-resistant sensitive to salicylhydroxamic acid oxidation pathway in detached etiolated cotyledons of yellow lupine (Lupinus luteus L.) and mitochondria isolated from these cotyledons were studied. Cotyledon treatment with 1 mM SA for 12 h increased the rate of oxygen uptake predominantly due to the activation of cyanide-resistant respiration (CRR) and alternative pathway of mitochondrial oxidation. It was established that the lupine genome encodes at least two isoforms of alternative oxidase (AO), LuAOX1 and LuAOX2, with the mol wt of about 35 kD. These proteins are always present in the mitochondria of etiolated lupine cotyledons, but their level increased rapidly after cotyledon treatment with SA, probably by increasing the mRNA content of the corresponding genes. SA-induced expression of Aox genes was correlated with the activation of CRR and an increase in the maximal activity (capacity) of AO in both detached yellow lupine cotyledons and mitochondria isolated from them.     

Effects of the organophosphorus plant growth regulator melaphen on structural characteristics of animal and plant membranes

Effects of low (from 4 × 10^?12 to 2 × 10^?7 M) doses of the organophosphorus plant growth regulator Melaphen on structural characteristics of plant and animal cellular membranes were compared with special reference to changes in the microviscosity of free membrane lipid bilayers and annular lipids bound to protein clusters. It was found that effective concentrations of Melaphen were not only different for animal and plant membranes, but also discrete and equal to 2 × 10^?7 or 4 × 10^?12 M depending on the membrane origin and the nature of membrane lipid components. In parallel experiments, effects of Melaphen on the rate of lipid peroxidation (LPO) in biological membranes were studied under conditions of external cold stress. The intensity of LPO was decreased at all Melaphen concentrations able to modulate the microviscosities of free and annular membrane lipids. It is concluded that effects of low and ultra-low Melaphen concentrations on structural and functional states of biological membranes of plant and animal origin are mediated by its interaction with signaling receptors of cellular membranes and cell organelles of both plant and animal origin.     

Organophosphorous plant growth regulator Melaphen: Resistance of plant and animal cells to stress factors

The addition of the organophosphorous plant growth regulator Melaphen (4 × 10^?12 M) to the incubation medium increases the maximum rate of oxidation of NAD-dependent substrates in rat liver and sugar beet root mitochondria. In addition, Melaphen stimulates electron transport during oxidation of succinate by rat liver mitochondria, but has no effect on the rate of this substrate oxidation in sugar beet root mitochondria. In storage organs of plants, the rate of oxidation of NAD-dependent substrates by mitochondria is relatively low. By stimulating the activity of NAD-dependent dehydrogenases, Melaphen stimulates energy metabolism in the cells and manifests adaptogenic activity by accelerating the germination of seeds. Melaphen does not influence the fluorescence of lipid peroxidation (LPO) products in mitochondria non-exposed to stress, but decreases 1.5–2 fold the LPO fluorescence in rat liver mitochondria exposed to cold stress and artificially “aged” sugar beet root mitochondria. Besides, Melaphen increases the rate of electron transport in a terminal site of respiratory chains of plant and animal mitochondria and decreases LPO. The data obtained testify to antistress activity of Melaphen.     

Involvement of the energy-dissipating systems in modulating the energetic efficiency of respiration in mitochondria from etiolated winter wheat seedlings

Effects of cyanide-resistant alternative oxidase (AOX) and modulators of plant uncoupling mitochondrial proteins (PUMP) on respiration rate and generation of transmembrane electric potential (ΔΨ) were investigated during oxidation of various substrates by isolated mitochondria from etiolated coleoptiles of winter wheat (Triticum aestivum L.). Oxidative phosphorylation in wheat mitochondria during malate and succinate oxidation was quite effective (it was characterized by high respiratory control ratio as defined by Chance, high ADP/O ratio, and rapid ATP synthesis). Nevertheless, the effectiveness of oxidative phosphorylation was substantially modulated by operation of energy-dissipating systems. The application of safranin dye revealed the partial dissipation of ΔΨ during inhibition of cytochrome-mediated malate oxidation by cyanide and antimycin A and demonstrated the operation of AOX-dependent compensatory mechanism for ΔΨ generation. The complex I of mitochondrial electron transport chain was shown to play the dominant role in ΔΨ generation and ATP synthesis during AOX functioning upon inhibition of electron transport through the cytochrome pathway. Effects of linoleic acid (PUMP activator) at physiologically low concentrations (4–10 μM) on respiration and ΔΨ generation in mitochondria were examined. The uncoupling effect of linoleic acid was shown in activation of the State 4 respiration, as well as in ΔΨ dissipation; this effect was eliminated in the presence of BSA but was insensitive to purine nucleotides. The uncoupling effect of linoleic acid was accompanied by reversible inhibition of AOX activity. The results are discussed with regard to possible physiological role of mitochondrial energy-dissipating systems in regulation of energy transduction in plant cells under stress conditions.     

Effect of Melatonin and Salicylic Acid on ROS Generation by Mitochondria of Lupine Seedlings

Russian Journal of Plant Physiology - The effect of melatonin and salicylic acid (SA) on respiration and ROS (hydrogen peroxide) generation during the oxidation of succinate by mitochondria...