Influence of mitochondrial genome rearrangement on cucumber leaf carbon and nitrogen metabolism

The MSC16 cucumber (Cucumis sativus L.) mitochondrial mutant was used to study the effect of mitochondrial dysfunction and disturbed subcellular redox state on leaf day/night carbon and nitrogen metabolism. We have shown that the mitochondrial dysfunction in MSC16 plants had no effect on photosynthetic CO2 assimilation, but the concentration of soluble carbohydrates and starch was higher in leaves of MSC16 plants. Impaired mitochondrial respiratory chain activity was associated with the perturbation of mitochondrial TCA cycle manifested, e.g., by lowered decarboxylation rate. Mitochondrial dysfunction in MSC16 plants had different influence on leaf cell metabolism under dark or light conditions. In the dark, when the main mitochondrial function is the energy production, the altered activity of TCA cycle in mutated plants was connected with the accumulation of pyruvate and TCA cycle intermediates (citrate and 2-OG). In the light, when TCA activity is needed for synthesis of carbon skeletons required as the acceptors for NH4+ assimilation, the concentration of pyruvate and TCA intermediates was tightly coupled with nitrate metabolism. Enhanced incorporation of ammonium group into amino acids structures in mutated plants has resulted in decreased concentration of organic acids and accumulation of Glu

Effects of turnip crinkle virus infection on the structure and function of mitochondria and expression of stress proteins in turnips

We have investigated the effect of turnip crinkle virus (TCV) infection on mitochondrial structure and function in turnips (Brassica rapa cultivar “Just Right”). TCV infection resulted in plants with small, mottled leaves with severely crinkled edges, and in a 46% reduction in storage root mass. TCV infection resulted in specific vesicularization of mitochondrial outer membranes where TCV replication is thought to occur, with no apparent affect on other cellular membrane systems. Immunoblot analysis of mitochondrial proteins from storage roots indicated that the TCV p28 protein, which is essential for viral replication, was associated with mitochondria and that mitochondrial heat shock protein 70 and cpn60 levels increased upon TCV infection. Isolation of mitochondrial outer membranes further showed TCV p28 protein enrichment in the outer membrane as compared with total mitochondrial proteins or total cellular proteins. Analysis of mitochondrial electron transport chain activities indicated that TCV infection resulted in a 54% decrease in exogenous NADH-dependent oxygen uptake and a 8% decrease in succinate- dependent oxygen uptake. Together these results indicate that TCV infection induces a stress response in mitochondria and a reduction in the ability of mitochondria to supply adenosine 5’-triphosphate to the cell

Alternative NAD(P)H dehydrogenases of plant mitochondria

Plant mitochondria have a highly branched electron transport chain that provides great flexibility for oxidation of cytosolic and matrix NAD(P)H. In addition to the universal electron transport chain found in many organisms, plants have alternative NAD(P)H dehydrogenases in the first part of the chain and a second oxidase, the alternative oxidase, in the latter part. The alternative activities are nonproton pumping and allow for NAD(P)H oxidation with varying levels of energy conservation. This provides a mechanism for plants to, for example, remove excess reducing power and balance the redox poise of the cell. This review presents our current understanding of the alternative NAD(P)H dehydrogenases present in plant mitochondria