Effect of salicylic acid on the metabolic activity of plant mitochondria

The effects of salicylic acid (SA) on mitochondrial respiration and generation of membrane potential across the inner membrane of mitochondria isolated from stored taproots of sugar beet (Beta vulgaris L.) and etiolated seedling cotyledons of yellow lupine (Lupinus luteus L.) were studied. When malate was oxidized in the presence of glutamate, low SA concentrations (lower than 1.0 mM) exerted predominantly uncoupling action on the respiration of taproot mitochondria: they activated the rate of oxygen uptake in State 4 (in the absence of ADP) and did not affect oxidation in State 3 (in the presence of ADP). In contrast, in lupine cotyledon mitochondria these SA concentrations inhibited oxygen uptake in the presence of ADP and much weaker activated substrate oxidation in State 4. Thus, SA (0.5 mM) reduced the respiratory control ratio according to Chance (RCR) by 25% in the taproots and 35% in cotyledons. When the concentration of phytohormone was increased (above 1.0 mM), malate oxidation in State 3 was inhibited and in State 4 — activated independently of the plant material used. In this case, the values of RCR and ADP/O were reduced by 50–60%. The effect of high SA concentrations (2 mM and higher) on malate oxidation depended on the duration of incubation and had a biphasic pattern: the initial activation of oxygen uptake was later replaced by its inhibition. The parallel studying the SA effect on the generation of membrane potential (ΔΨ) at malate oxidation in the mitochondria of beet taproots and lupine cotyledons showed that ΔΨ dissipation was observed because of SA uncoupling and inhibiting action on respiration. The degree of ΔΨ dissipation depended on the phytohormone concentration and duration on mitochondria treatment, especially at its high concentrations. In general, a correlation was found between the effects of SA on mitochondrial respiration and ΔΨ values in the coupling membranes. Furthermore, these results show that the responses of mitochondria to SA were determined not only by its concentration but also by treatment duration and evidently by the sensitivity to the phytohormone of mitochondria isolated from different plant tissues.     

OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA OF DEVELOPING RAT BRAIN

Abstract—

• 1 Oxygen uptake, ADP/O ratios and respiratory control ratios (RCR) were studied by oxygen electrode techniques in mitochondria prepared from developing rat brain.
• 2 Oxygen consumption, ADP/O ratios and RCR based on mitochondrial protein concentration increased with maturation. Of the substrates employed, succinate supported oxygen uptake best and malate poorest.
• 3 The addition of exogenous NAD to the mitochondrial preparation had no effect on rate of oxygen uptake.
• 4 Lack of change in ADP/O ratio in the presence of glucose, a tricarboxylic acid cycle intermediate (α-oxoglutarate), and ATP leads us to believe that there is no significant hexokinase activity in this preparation.

     

Mitochondrial respiration in heart, liver, and kidney of copper-deficient rats

Morphological observations in some tissues indicate that dietary copper deficiency results in structural damage to mitochondria. The purpose of this study was to determine whether mitochondrial function is impaired as well. Male, weanling Sprague-Dawley rats were fed diets deficient or sufficient in copper for 4 weeks. Mitochondria were isolated from heart, liver, kidney cortex, and kidney medulla. P/O ratio, state 3 and state 4 respiration rates (oxygen consumed in the presence and absence of ADP, respectively), and acceptor control index (ratio of state 3:state 4) were determined using succinate or pyruvate/malate as substrate. State 3 respiration rate in mitochondria from copper-deficient hearts and livers was lower than in mitochondria from copper-sufficient hearts. Copper deficiency reduced the state 4 respiration rate only in cardiac mitochondria. Neither respiration rate was affected by copper deficiency in mitochondria from kidney medulla or cortex. P/O ratio was not significantly affected by copper deficiency in any tissue examined. Acceptor control index was reduced only in liver mitochondria. The observed decreases in respiration rates are consistent with decreased cytochrome c oxidase activity, shown by others to occur in mitochondria isolated from hearts and livers of copper-deficient rats.     

Salt Tolerance in Suaeda maritima (L.) Dum: THE EFFECT OF SODIUM CHLORIDE ON GROWTH, RESPIRATION, AND SOLUBLE ENZYMES IN A COMPARATIVE STUDY WITH PISUM SATIVUM L

The effect of sodium, chloride on the growth of a halophyte,Suaeda maritima (L.) Dum., was compared with its effect on Pisumsativum L. cv. Alaska under controlled environmental conditions.The salt stimulated the growth of Suaeda maximally at concentrationsof 170 to 340 mM while the growth of Pisum was inhibited evenby 100 mM. Both species accumulated ions in the tops and themaximum concentrations of Na⁺ and Cl^– rose in Suaeda to860 mM (based on the water content) and 730 mM and in Pisumto 170 mM and 300 mM respectively. Respiration in both specieswas inhibited as the NaCl level in the culture solution wasraised. Four supernatant enzymes (malic dehydrogenase, glucose-6-phosphatedehydrogenase, peroxidase, and acid phosphatase) prepared fromPisum and from Suaeda (grown either in the absence of addedNaCl or in the presence of 340 mM NaCl) were assayed in variouslevels of sodium chloride. The dehydrogenases were markedlyinhibited by increasing salt concentrations while there wasa smaller effect on the peroxidase and acid phosphatase. Therewas no difference in the effect of salt on the enzymes preparedfrom the two species although one is halophilic and the otherhalophobic.     

Effects of Fluoride on Mitochondrial Activity in Higher Plants

The effects of fluoride on respiration of plant tissue and mitochondria were investigated. Fumigation of young soybean plants (Glycine max Merr. cv. Hawkeye) with 9–12 μg × m^?3 HF caused a stimulation of respiration at about 2 days of treatment followed by inhibition 2 days later. Mitochondria isolated from the stimulated tissue had higher respiration rates, greater ATPase activity, and lower P/O ratios, while in mitochondria from inhibited tissue, all three were reduced. Treatment of etiolated soybean hypocotyl sections in Hoagland's solution containing KF for 3 to 10 h only resulted in inhibition of respiration. Mitochondria isolated from this tissue elicited increased respiration rates with malate as substrate and inhibited respiration with succinate. With both substrates respiratory control and ADP/O ratios were decreased. Direct treatment of mitochondria from the etiolated soybean hypocotyl tissue with fluoride resulted in inhibition of state 3 respiration and lower ADP/O ratios with the substrates succinate, malate, and NADH. Fluoride was also found to increase the amount of osmotically induced swelling and cause a more rapid leakage of protein with mitochondria isolated from etiolated corn shoots (Zea mays L. cv. Golden Cross Bantam). The results are discussed with respect to possible effects of fluoride on mitochondrial membranes.     

Control of oxidative phosphorylation by the extramitochondrial ATP/ADP ratio

The control of mitochondrial ATP synthesis by the extramitochondrial adenine nucleotide pattern was investigated with rat liver mitochondria. It is demonstrated that any stationary state between the two limit states of maximum activity (state 3) and of resting activity (state 4) can be obtained by a hexokinase-glucose trap as an ADP-regenerating system. These intermediate states are characterized by stationary respiratory rates, stationary redox levels of the cytochromes b and c and stationary levels of extramitochondrial ATP and ADP between the rates and levels of the limit states. At a constant concentration of inorganic phosphate the activity of mitochondria between the limit states is controlled by the extramitochondrial ATP/ADP ratio independent of the total concentration of adenine nucleotides present. The control range was found to be between ratios of about 5 and 100 at 10 mM phosphate. At lower ratios the mitochondria are in their maximum phosphorylating state. With succinate + rotenone and glutamate + malate the same control range was observed, indicating that it is independent of the nature of substrate oxidized.The results suggest that in the control range the mitochondrial activity is limited by the competition of ADP and ATP for the adenine nucleotide translocator.     

Malate Decarboxylation by Mitochondria of the Inducible Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum

Mitochondria isolated from leaves of Mesembryanthemum crystallinumoxidized malate by both NAD malic enzyme and NAD malate dehydrogenase.Rates of malate oxidation were higher in mitochondria from plantsgrown at 400 mil NaCl in the rooting medium and performing Crassulaceanacid metabolism (CAM) than in mitochondria from plants grownat 20 mM NaCl and exhibiting C₃-photosynthetic CO₂ fixation.The mitochondria isolated from plants both in the CAM and C₃modes were tightly coupled and gave high respiratory control.At optimum pH for malate oxidation (pH 7.0), pyruvate was themajor product in mitochondria from CAM-M. crystallinum, whereasmitochondria from C₃-M. crystallinum produced predominantlyoxaloacetate. Both the extracted NAD malic enzyme in the presenceof CoA and the oxidation of malate to pyruvate by the mitochondriafrom plants in the CAM mode had a pH optimum around 7.0 withactivity declining markedly above this pH. The activity of NAD-malicenzyme, expressed on a cytochrome c oxidase activity basis,was much higher in mitochondria from the CAM mode than the C₃mode. The results indicate that mitochondria of this speciesare adapted to decarboxylate malate at high rates during CAM. ¹Current address: Lehrstuhl für Botanik II, UniversitätWurzburg, Mittlerer Dallenbergweg 64, 8700 Würzburg, WestGermany. ²Current address: KD 120, Chemical Research Division, OntarioHydro, 800 Kipling Avenue, Toronto, Ontario M8Z5S4, Canada. ³Current address: Department of Botany, Washington State University,Pullman, Washington 99164-4230, U.S.A. (Received March 13, 1986; Accepted September 18, 1986)     

Ferrous-iron induces lipid peroxidation with little damage to energy transduction in mitochondria

Addition of ferrous sulfate, but not ferric chloride, in micromolar concentrations to rat liver mitochondria induced high rates of consumption of oxygen. The oxygen consumed was several times in excess of the reducing capacity of ferrous-iron (O: Fe ratios 5–8). This occurred in the absence of NADPH or any exogenous oxidizable substrate. The reaction terminated on oxidation of ferrous ions. Malondialdehyde (MDA), measured as thiobarbituric acid-reacting material, was produced indicating peroxidation of lipids. The ratio of O₂: MDA was about 4: 1. Pretreatment of mitochondria with ferrous sulfate decreased the rate of oxidation (state 3) with glutamate (+malate) as the substrate by about 40% but caused little damage to energy tranduction process as represented by ratios of ADP: O and respiratory control, as well as calcium-stimulated oxygen uptake and energy-dependent uptake of [⁴⁵Ca]-calcium. Addition of succinate or ubiquinone decreased ferrous iron-induced lipid peroxidation in intact mitochondria. In frozen-thawed mitochondria, addition of succinate enhanced lipid peroxidation whereas ubiquinone had little effect. These results suggest that ferrous-iron can cause peroxidation of mitochondrial lipids without affecting the energy transduction systems, and that succinate and ubiquinone can offer protection from damage due to such ferrous-iron released from the stores within the cells.     

Respiratory control in hyperpermeable adult heart muscle cells Effects of calcium

Spontaneously beating myocardial fragments prepared by mechanical disaggregation have hyperpermeable sarcolemmae. Such preparations were used to study mitochondrial function in situ. The myocardial fragments suspended in a phosphate-buffered salt solution containing 1–3 mM MgCl₂ showed a low rate of oxygen uptake. Addition of succinate, pyruvate plus malate or glutamate was followed by an increase in the rate of O₂ uptake. Addition of ADP to fragments engaged in State 4 respiration was followed by initiation of more rapid State 3 respiration, with respiratory control ratios routinely greater than 3 for succinate and glutamate. If the fragments were suspended in the same medium containing 3 mM ATP (a medium in which contractile activity occurs), State 3 was initiated upon addition of substrate. The suspension medium used in these experiments contained about 8 μM calcium as contamination. Addition of calcium chloride to give a final concentration of 0.14 to 0.57 mM stimulated State 4 respiration of the myocardial fragments. In contrast, similar additions made during State 3 inhibited respiration. The maximum degree of inhibition brought respiration close to the State 4 rate. If calcium was added prior to ADP, respiratory stimulation by the nucleotide was diminished. Respiratory function of myocardial fragments and of mitochondria isolated from them was similar in terms of response to substrate, ADP, and calcium addition in State 4. Response to calcium in State 3 was different in that inhibition was long-lived only at low [P_i] in the case of mitochondria, but at low or high [P_i] in the case of the fragments.     

THE EFFECT OF SODIUM CHLORIDE CONCENTRATION ON GROWTH AND EGG LAYING OF HELISOMA DURYI, BIOMPHALARIA ALEXANDRINA AND BULINUS TRUNCATUS (GASTROPODA: PLANORBIDAE)

Helisoma duryi, Biomphalaria alexandrine and Bulinus truncatuswere maintained in media with seven different sodium chlorideconcentrations ranging from 0.6 to 32 mM. Growth of H. duryiwas significantly reduced only in the 32 mM NaCl treatment,while no significant effects were observed in the net reproductiverate or in egg-laying rates. Bulinus truncatus showed optimalgrowth within the range of 1 to 8 mM NaCl and the net reproductiveand egg-laying rates were reduced in the 32 mM NaCl treatment.Growth of B. alexandrina was reduced in the 16 and 32 mM NaCltreatments, while the net reproductive rate was reduced in the16 and 32 mM NaCl treatments, while the net reproductive ratewas reduced in media with more than 2.0 mM NaCl. Hatching ofB. truncatus eggs was not affected by the high NaCl concentrations,while the hatchability of H. duryi eggs was reduced in the 32mM treatment. Survival of newly-hatched H. duryi was best inthe 1 mM NaCl treatment while for B. truncatus survival wasreduced only in the 32 mM treatment. (Received 28 March 1988; accepted 7 April 1989)     

Preparation and properties of mitochondria from cowpea nodules

Mitochondria were isolated from nodules of cowpea (Vigna unguiculata (L). Walp.) and purified on a Percoll gradient. They were only slightly contaminated by bacteroids (an average of 3.5%), and had low lipoxygenase activity. Compared to mitochondria from hypocotyls the nodule mitochondria had similar O₂ uptake rates and respiratory control ratios. The ADP/O ratios for both preparations were 1.4 to 1.7 and 2.3 to 2.6 with succinate and malate, respectively. Whereas mitochondria isolated from etiolated cowpea hypocotyls had 14 to 18% of their respiration insensitive to KCN, the respiration of nodule mitochondria was completely inhibited by KCN. Enzyme activities of nodule mitochondria were similar to those found in hypocotyl mitochondria, except for NAD⁺-malic enzyme which was 12-fold lower in the mitochondria from nodules.     

Plant Desiccation and Protein Synthesis. IV. RNA Synthesis, Stability, and Recruitment of RNA into Protein Synthesis during Desiccation and Rehydration of the Desiccation-Tolerant Moss, Tortula ruralis

We have studied the effects of ATP and ADP on the oxidation of malate by coupled and uncoupled mitochondria prepared from etiolated hypocotyls of mung bean (Vigna radiata L.).

In coupled mitochondria, ATP (1 millimolar) increased pyruvate production and decreased oxaloacetate formation without altering the rate of oxygen consumption. ATP also significantly decreased oxaloacetate production and increased pyruvate production in mitochondria that were uncoupled by carbonyl cyanide p-trifluoromethoxyphenyl hydrazone plus oligomycin.

In coupled mitochondria, ADP (1 millimolar) increased the production of both pyruvate and oxaloacetate concomitantly with the acceleration of oxygen uptake to the state 3 rate. The effects of ADP were largely eliminated in uncoupled mitochondria. These results indicate that, whereas the ADP stimulation of oxaloacetate and pyruvate production in the coupled mitochondria is brought about primarily as the result of the accelerated rates of electron transport and NADH oxidation by the respiratory chain in state 3, ATP has significant regulatory effects independent of those that might be exerted by control of electron transport.

     

Mitochondrial Changes in Harvested Carnation Flowers (Dianthus caryophyllus L.) during Senescence

Harvested carnation (Dianthus caryophyllus L.) flowers wereplaced in either a preservative solution or deionized waterand monitored through senescence during which time flower freshweight was measured as well as production of ethylene and CO₂.Flower fresh weight, ethylene, and CO₂ levels increased as theflowers aged, but fresh weight and CO₂ levels fell once flowersbegan to senesce regardless of holding solution. Preservative-treatedflowers senesced at a slower rate than deionized water-treatedflowers. The amount of ADP phosphorylated to ATP per oxygenatom consumed, using mitochondria isolated from petal tissueprovided with either succinate or malate as substrates, wasfound to increase as flowers senesced and then to decrease inthe later stages of senescence. Respiratory control ratios withsuccinate as the substrate did not change appreciably untilthe final stages of senescence white respiratory control valuesusing malate showed greater variation but no consistent patternrelative to the progress of senescence. Cyanide-resistant respirationwas noted with isolated mitochondria oxidizing either substrate,but no correlation between cyanide-resistant respiration andsenescence could be found. (Received July 10, 1984; Accepted April 16, 1985)     

The Respiratory Chain of Plant Mitochondria. II. Oxidative Phosphorylation in Skunk Cabbage Mitochondria

Mitochondria were prepared from the spadices of skunk cabbage (Symplocarpus foetidus) whose respiratory rate with succinate and malate showed 15% to 30% sensitivity to cyanide inhibition, and which showed respiratory control by added ADP. The observed respiratory control ratios ranged from 1.1 to 1.4. The change in pH of the mitochondrial suspension was recorded simultaneously with oxygen uptake: alkalinization of the medium, expected for phosphorylation of ADP, coincided with the period of acceleration in oxygen uptake caused by addition of an ADP aliquot. The ADP/O ratios obtained were 1.3 for succinate and 1.9 for malate. In the presence of 0.3 mm cyanide, the ADP/O ratio for succinate was zero, while that for malate was 0.7. These results are consistent with the existence of an alternate oxidase which interacts with the flavoprotein and pyridine nucleotide components of the respiratory chain and which, in the presence of cyanide, allows the first phosphorylation site to function with an efficiency of about 70%. In the absence of respiratory inhibitors, the efficiency of each phosphorylation site is also about 70%. This result implies that diversion of reducing equivalents through the alternate oxidase, thereby bypassing the 2 phosphorylation sites associated with the cytochrome components of these mitochondria, occurs to a negligible extent during the oxidative phosphorylation of ADP or State 3.Addition of ADP or uncoupler to skunk cabbage mitochondria respiring in the controlled state or State 4, results in reduction of cytochrome c and the oxidation of the cytochromes b, ubiquinone and pyridine nucleotide. A site of interaction of ADP with the respiratory chain between cytochromes b and cytochrome c is thereby identified by means of the crossover theorem. Flavoprotein measured by fluorescence is also oxidized upon addition of ADP or uncoupler, but flavoprotein measured by optical absorbance changes becomes more reduced under these conditions. Depletion of the mitochondria by pretreatment with ADP and uncoupler prevents reduction of most of the fluorescent flavoprotein by succinate. These results indicate that skunk cabbage mitochondria contain both high and low potential flavo-proteins characterized by different fluorescence/absorbance ratios similar to those demonstrated to be part of the respiratory chain in mitochondria from animal tissues.     

Effect of phosphate and uncouplers on substrate transport and oxidation by isolated corn mitochondria

A study was made to determine conditions under which malate oxidation rates in corn (Zea mays L.) mitochondria are limited by transport processes. In the absence of added ADP, inorganic phosphate increased malate oxidation rates by processes inhibited by mersalyl and oligomycin, but phosphate did not stimulate uncoupled respiration. However, the uncoupled oxidation rates were inhibited by butylmalonate and mersalyl. When uncoupler was added prior to substrate, subsequent O₂ uptake rates were reduced when malate and succinate, but not exogenous NADH, were used. Uncoupler and butylmalonate also inhibited swelling in malate solutions and malate accumulation by these mitochondria, which were found to have a high endogenous phosphate content. Addition of uncoupler after malate or succinate produced an initial rapid oxidation which declined as the mitochondria lost solute and contracted. This decline was not affected by addition of ADP or AMP, and was not observed when exogenous NADH was substrate. Increasing K⁺ permeability with valinomycin increased the P-trifluoromethoxy (carboxylcyanide)phenyl hydrazone inhibition. Kinetic studies showed the slow rate of malate oxidation in the presence of uncoupler to be characterized by a high Km and a low V_max, probably reflecting a diffusion-limited process.     

Sodium Chloride Compartmentation in Leaf Vacuoles of the Halophyte Suaeda maritima (L.) Dum. and its Relation to Tonoplast Permeability

Single channel properties, whole vacuole currents and protonpumping capacity were investigated in the intact vacuoles andmembrane patches of leaf tonoplast from the halophyte Suaedamaritima. ATP-dependent proton pumping capacity was similarto non-halophytes whether the plants were or were not grownwith added sodium chloride (200 mM). The most abundant ion channelwas inward rectifying and had a single channel conductance of58 pS in symmetrical KCl solutions (100 mM) to 170 pS usingphysiological conditions (50/150 mM KCl/NaCl cytoplasmic side,50/450 mM KCl/NaCl vacuolar side). The channel showed all thecharacteristics of the SV type channel described in many otherspecies. In the open state these channels caused tonoplast conductancesin excess of 0.5 nS m²– but conductances were much lowerusing physiological ion concentrations and membrane potentials.In spite of the poor selectivity and the potentially large tonoplastconductance it is calculated that compartmentation of NaCl inleaf vacuoles can be sustained by about 30% of ATP-dependentproton pumping capacity. The results do not indicate any specialadaptation of the tonoplast ion channels in the halophyte. Key words: Ion-channels, patch-clamp, salt-tolerance, vacuole     

Adenosine diphosphate and calcium stimulation of respiration in mitochondria from alloxan diabetic rats

Liver mitochondria from normal and alloxan diabetic rats, isolated in 0.25 M sucrose, were assayed with an oxygen electrode for ADP/O and Ca⁺²/O ratios, respiratory ratio, and respiratory control index. Mitochondria were incubated with two substrates, succinate and β-hydroxybutyrate; two types of ionic media, Na⁺ medium (Na⁺ the major monovalent cation) and K⁺ medium (K⁺ the major monovalent cation); and two respiratory stimulants, ADP (352 μM) and Ca⁺² (187 μM). Significant differences between respiratory rates and ADP/O ratios were dependent upon the substrate and ionic medium employed. The results confirm previous studies which showed no alteration in ADP/O ratio but decreased State 3 respiratory rates under similar conditions of K⁺ medium with ADP stimulation in the diabetic. Furthermore, the State 3 respiration was prolonged compared to normal. Ca⁺² stimulation was the same in normal and diabetic mitochondria in K⁺ medium. Studies in Na⁺ media revealed more significant differences in RCI's, respiratory rates, and ADP/O ratios that were substrate dependent as well as ion dependent. The results from these various studies can be accounted for by an hypothesis linking mitochondrial K⁺ interaction with alterations in the diabetic mitochondria.     

The nature of the oxidation states of sweet potato mitochondria

Sweet potato mitochondria exhibited respiratory control duringthe oxidation of malate and succinate with ADP/O ratios approachingthe theoretical P/O values. Prior to the addition of ADP themitochondria showed a considerable rate of substrate oxidation,defined as the basic respiration, which was of the same magnitudeas state 4 respiration. Electrons from state 4 and the basicrespiration were at least partially mediated by the cytochromechain, as shown by effects of cyanide, azide and amytal, andby spectrophotometric evidence. The nature of ATPase was studied and the influence of inhibitorsof ATPase activity on oxidation helped to establish the relationshipbetween the several states of oxidation and ATPase activity.The ADP/O ratio and ADP-stimulated respiration were slightlydecreased by fluoride, while state 4, the basic respirationand ATPase activity were effectively inhibited. Chlorpromazineinhibited DNP-stimulated ATPase activity, respiration uncoupledby DNP and all the states of malate oxidation. However, state4 and basic respiration were less sensitive than was state 3of malate oxidation to 0.3 mM chlorpromazine. It was concluded that mitochondrial ATPase played a role inthe basic respiration and in state 4 oxidation. ¹Present address: Department of Biochemistry Tel-Aviv University,Tel-Aviv, Israel (Received August 1, 1969; )     

Salt-induced Pinocytosis in Barley and Bean

The ultrastructure of the halophyte, Salicornia europea L. wascompared with barley and bean plants grown under saline conditions.S. europea exhibited frequent pinocytotic vesiculation in thehypocotyl and stem but less vesiculation in the root and cotyledon.No vesiculation was observed in barley and bean plants grownin the absence of sodium chloride though plants grown in thepresence of sodium chloride demonstrated vesiculation, morein barley than in bean. Both the halophyte and the glycophytesdemonstrated more pinocytosis in the plant tops than in theroot system. The multivesiculate structures observed were connectedto the wall free space at the early stages of their formationand have not been reported in plants under normal physiologicalconditions. The observations on pinocytosis are discussed in relation totoxic ion compartmentation and salt resistance in plants.     

Some effects of decenylsuccinic Acid on isolated corn mitochondria

The effects of decenylsuccinic acid on the swelling and respiratory capacities of mitochondria isolated from etiolated corn (Zea mays L., Wf9 × M14) shoots were studied. Decenylsuccinic acid (0.1 mM to 1.0 mM) inhibited the oxidation of succinate and malate-pyruvate, stimulated the oxidation of reduced nicotinamide adenine dinucleotide, and uncoupled phosphorylation. The swelling of isolated corn mitochondria, as determined by percentage of transmittance changes, was stimulated by decenylsuccinic acid in potassium chloride reaction media and in sucrose reaction media without bovine serum albumin. In a diaphorase (2, 6-dichlorophenolindophenol as acceptor) reaction with intact mitochondria, only the dehydrogenation rate of malate was reduced by the addition of decenylsuccinic acid. The dehydrogenation of reduced nicotinamide adenine dinucleotide or of succinate was either not affected or was stimulated depending on the diaphorase reaction medium. The oxygen uptake of mitochondria oxidizing N, N, N′, N′-tetramethyl-p-phenylenediamine diHCl and ascorbate was inhibited at decenylsuccinic acid concentrations greater than 0.5 mM.