Alternate oxidase (original) (raw)
Related papers
Physiology and Molecular Biology of Plants, 2008
Plant respiration, similar to respiration in animal mitochondria, exhibits both osmosensitive and insensitive components with the clear distinction that the insensitive respiration in plants is quantitatively better described as 'less' sensitive rather than 'insensitive'. Salicylic hydroxamic acid (SHAM)-sensitive respiration was compared with the respiration sensitive to other inhibitors in rice, yeast and Dunaliella salina. The influence of SHAM was largely in the osmotically less sensitive component and enhanced with external osmotic pressure unlike other inhibitors that inhibited the osmotically sensitive component. SHAM inhibited germination and root growth but not shoot growth. Osmotic remediation of respiration that developed in due course of time with rice seedlings was abolished by SHAM and was not due to water and ionic uptake mechanisms. Yeast and Dunaliella also showed susceptibility of growth and respiration to SHAM. Glycerol retention was influenced by all inhibitors, while growth was inhibited demonstrably by SHAM in Dunaliella. Respiration in plants needs to be seen as a positive contribution to overall growth and not merely for burning away of the biomass. [Physiol. Mol. Biol. Plants 2008; 14(3) : 235-251]
Regulation of alternative oxidase activity in higher plants
Journal of Bioenergetics and Biomembranes, 1995
The activity of the alternative pathway is affected by a number of factors, including the level and reduction state of the alternative oxidase (AOX) protein, and the reduction state of the ubiquinone pool. To investigate the significance of these factors for the rate of alternative respiration in vivo, we studied root respiration of six wild monocotyledonous grass species that were grown under identical controlled conditions. The activity of the alternative pathway was determined using the oxygen isotope fractionation technique. In all species, the AOX protein was invariably in its reduced (high activity) state. There was no correlation between AOX activity and AOX protein concentration, ubiquinone (total, reduced, or oxidized) concentration, or the reduction state of the ubiquinone pool. However, when some of these factors are combined in a linear regression model, a good fit to AOX activity is obtained. The function of the AOX is still not fully understood. It is interesting that we found a positive correlation between the activity of the alternative pathway and relative growth rate; a possible explanation for this correlation is discussed. Inhibition of the AOX (with salicylhydroxamic acid) decreases respiration rates less than the activity present before inhibition (i.e. measured with the 18 O-fractionation technique).
PLANT PHYSIOLOGY, 1986
ABSTRACI Low concentrations of salicylhydroxamic acid (<5 millimolar) stimulate 02 uptake in intact roots of Pisum sativum. We demonstrate that the hydroxamate-stimulated 02 uptake does not reside in the mitochondria. We also show that the hydroxamate-stimulated 02 uptake is due to the activation of a peroxidase catalyzing reduction of 02. This peroxidase, which can use both NADH and NADPH as a substrate, is stimulated by low concentrations of monophenols, e.g. salicylhydroxamic acid and 2methoxyphenol. It is inhibited by high (20 millimolar) concentrations of salicylhydroxamic acid, cyanide, and scavengers of the superoxide free radical ion, e.g. ascorbate, gentisic acid, and catechol. In the presence of gentisic acid, 02 uptake by intact pea roots was no longer stimulated by low concentrations of salicylhydroxamic acid. The consequence of the present finding for in vivo respiration measurements is that the use of low concentrations of salicylhydroxamic acid and uncoupler is reliable only in the presence of a suitable superoxide free radical scavenger which prevents activation of the peroxidase. It also confirms that high concentrations of salicylhydroxamic acid (20-25 millimolar) can be safely used in short-term experiments to assess the activity of the alternative path in intact roots. Substituted hydroxamic acids, e.g. SHAM4, are widely used as specific inhibitors of the alternative pathway, both in vitro (17) and in vivo (13). However, De Visser and Blacquiere (8) found that SHAM, at concentrations below 15 mm, stimulates 02 uptake in pea roots. The maximum stimulation by low (1-5 mM) concentrations of SHAM was approximately 40% of the control respiration. This 02 uptake was resistant to antimycin and inhibited by 0.4 mm KCN and high (20-25 mM) concentrations of SHAM. The same system which was activated by low concentrations of SHAM could also be stimulated by uncoupler (2 gM CCCP) (8). The location and the nature of this system are so far unknown. ' Supported in part by the Foundation for Fundamental Biological Research (BION) which is subsidized by the Netherlands Organization for the Advancement of Pure Research (ZWO). D. A. D. was the recipient of a grant from the Netherlands Organization for the Advancement of Pure Research (ZWO) while working on this project.
Regulation of Respiration and Fermentation to Control the Plant Internal Oxygen Concentration
PLANT PHYSIOLOGY, 2008
Plant internal oxygen concentrations can drop well below ambient even when the plant grows under optimal conditions. Using pea (Pisum sativum) roots, we show how amenable respiration adapts to hypoxia to save oxygen when the oxygen availability decreases. The data cannot simply be explained by oxygen being limiting as substrate but indicate the existence of a regulatory mechanism, because the oxygen concentration at which the adaptive response is initiated is independent of the actual respiratory rate. Two phases can be discerned during the adaptive reaction: an initial linear decline of respiration is followed by a nonlinear inhibition in which the respiratory rate decreased progressively faster upon decreasing oxygen availability. In contrast to the cytochrome c pathway, the inhibition of the alternative oxidase pathway shows only the linear component of the adaptive response. Feeding pyruvate to the roots led to an increase of the oxygen consumption rate, which ultimately led to anoxia. The importance of balancing the in vivo pyruvate availability in the tissue was further investigated. Using various alcohol dehydrogenase knockout lines of Arabidopsis (Arabidopsis thaliana), it was shown that even under aerobic conditions, alcohol fermentation plays an important role in the control of the level of pyruvate in the tissue. Interestingly, alcohol fermentation appeared to be primarily induced by a drop in the energy status of the tissue rather than by a low oxygen concentration, indicating that sensing the energy status is an important component of optimizing plant metabolism to changes in the oxygen availability.
Cellular Respiration on Plants
This experiment basically is designed to identify certain factors that are essential requirements in the process of cellular respiration and to better understand the factors that can affect the physiology of plants. Fundamentally, plants, during the process of cellular require the availability of oxygen (O2). Respiration is termed aerobic when oxygen is utilized and anaerobic when oxygen is not utilized. This process is used to form ATP and other energy carrying molecules (energy-liberating) that are used to provide energy for cellular work. Aside from ATP, the overall process is the complete oxidation of glucose that results to production of CO2 and H2O thus evolution of gasses occurs. During oxidation reactions, enzymes like oxidases, peroxidases and catalase are noticeable on its speeding effects.
Respiration in Plants Interacting with Pathogens, Pests and Parasitic Plants
2015
Growth and maintenance of plant cells require three basic metabolic ingredients: energy, in the form of adenosine triphosphate (ATP), reducing power, usually in the form of nicotinamide adenine dinucleotide phosphate (NADP; in reduced form, NADPH), and precursor molecules. In a photosynthetic cell in the light, these requirements are met by photosynthesis, while in non-photosynthetic cells, these requirements are met mainly by carbon compounds imported from leaves (Smith et al., 2010). Carbon is usually imported into non-photosynthetic tissues as sucrose, and this is metabolised initially to hexose phosphates, which in turn are metabolised further by three interrelated pathways: glycolysis, the oxidative pentose phosphate (OPP) pathway and tricarboxylic acid (TCA) cycle, also known as the Krebs cycle. These pathways provide the non-photosynthetic cell with all of their ATP, reducing power and precursor molecules. Of course, these three pathways also operate in photosynthetic tissues. The activities of these pathways are often referred to as 'dark respiration', to distinguish it from photorespiration, which is linked to photosynthesis via the unique carboxylase/oxygenase function of Rubisco (see the following section). Before we examine the effects of attack on respiration, let us look briefly at glycolysis, the TCA cycle and the OPP pathway. Glycolysis is a cytosolic pathway that converts glucose to pyruvate and in the process, results in a small net gain of ATP (Fig. 4.1). Under aerobic conditions, phosphofructokinase (PFK) is the main regulator of glycolysis and is responsible for the formation of fructose-1,6-bisphosphate from fructose-6-phosphate. The oxidative metabolism of pyruvate by pyruvate dehydrogenase (PDH) leads to the formation of acetyl-CoA, which enters the TCA cycle (Fig. 4.1). The latter is responsible for a major portion of carbohydrate, fatty acid and amino acid oxidation, producing energy and reducing power. Under conditions that are particularly energy demanding, production of pyruvate via glycolysis can occur faster than PDH can convert it to acetyl-CoA. However, pyruvate can be used to form succinate, in a process known as the 4-aminobutyrate (GABA) shunt, thereby providing a second entry point for pyruvate into the TCA cycle and a means of utilising excess pyruvate for energy production. The TCA cycle also generates reducing equivalents (e.g. NADH) that are used Physiological Responses of Plants to Attack, First Edition. Dale R. Walters.
Plant Physiology and Biochemistry
Kew Bulletin, 1965
Casuarina glauca is an actinorhizal tree which establishes root-nodule symbiosis with N 2 -fixing Frankia bacteria. This plant is commonly found in saline zones and is widely used to remediate marginal soils and prevent desertification. The nature of its ability to survive in extreme environments and the extent of Frankia contribution to stress tolerance remain unknown. Thus, we evaluated the ability of C. glauca to cope with salt stress and the influence of the symbiosis on this trait. To this end, we analysed the impact of salt on plant growth, mineral contents, water relations, photosynthetic-related parameters and nonstructural sugars in nodulated vs. non-nodulated plants. Although the effects on photosynthesis and stomatal conductance started to become measurable in the presence of 200 mM NaCl, photochemical (e.g., photosynthetic electron flow) and biochemical (e.g., activity of photosynthetic enzymes) parameters were only strongly impaired when NaCl levels reached 600 mM. These results indicate the maintenance of high tissue hydration under salt stress, probably associated with enhanced osmotic potential. Furthermore, the maintenance of photosynthetic assimilation potential (A max ), together with the increase in the quantum yield of down-regulated energy dissipation of PSII (Y NPQ ), suggested a downregulation of photosynthesis instead of photo-damaging effects. A comparison of the impact of increasing NaCl levels on the activities of photosynthetic (RubisCO and ribulose-5 phosphate kinase) and respiratory (pyruvate kinase and NADH-dependent malate dehydrogenase) enzymes vs. photosynthetic electron flow and fluorescence parameters, revealed that biochemical impairments are more limiting than photochemical damage. Altogether, these results indicate that, under controlled conditions, C. glauca tolerates high NaCl levels and that this capacity is linked to photosynthetic adjustments.