Respiratory supercomplexes are large protein structures formed by various enzyme complexes of the mitochondrial electron transport chain. Using native gel electrophoresis and activity staining, differential regulation of complex activity within the supercomplexes was investigated. During prolonged hypoxia, complex I activity within supercomplexes diminished, whereas the activity of the individual complex I-monomer increased. Concomitantly, an increased activity was observed during hypoxia for complex IV in the smaller supercomplexes that do not contain complex I. These changes in complex activity within supercomplexes reverted again during recovery from the hypoxic treatment. Acidification of the mitochondrial matrix induced similar changes in complex activity within the supercomplexes. It is suggested that the increased activity of the small supercomplex III₂+IV can be explained by the dissociation of complex I from the large supercomplexes. This is discussed to be part of a mechanism regulating the involvement of the alternative NADH dehydrogenases, known to be activated by low pH, and complex I, which is inhibited by low pH. It is concluded that the activity of complexes within supercomplexes can be regulated depending on the oxygen status and the pH of the mitochondrial matrix.

Growth parameters, the content of proline and flavonoids. Na+ and K+ion accumulation in the shoots of four species of halophytes from the family Chenopodiaceae inhabiting the territory of the South...

Brassinosteroids (BRs) represent a group of plant signaling molecules with a steroidal skeleton that play an essential role in plant adaptation to different environmental stresses, including drought. In this work, the effect of pretreatment with 0.4 µM 24-epibrassinolide (EBR) on the oxidant/antioxidant system in 4-day-old wheat seedlings (Triticum aestivum L.) was studied under moderate drought stress simulated by 12% polyethylene glycol 6000 (PEG). It was revealed that EBR-pretreatment had a protective effect on wheat plants as evidenced by the maintenance of their growth rate, as well as the reduction in lipid peroxidation and electrolyte leakage from plant tissues under drought conditions. This effect was likely due to the ability of EBR to reduce the stress-induced accumulation of reactive oxygen species (ROS) and modulate the activity of antioxidant enzymes. Meanwhile, EBR pretreatment enhanced proline accumulation and increased the barrier properties of the cell walls in seedlings by accelerating the lignin deposition. Moreover, the ability of EBR to prevent a drought-caused increase in the intensity of the total dark respiration and the capacity of alternative respiration contributes significantly to the antistress action of this hormone.

In the roots of bread wheat ( Triticum aestivumL.) seedlings, the effects of pretreatment with 28 nM wheat germ agglutinin (WGA) and successive action of 1 mM cadmium acetate on growth, phytohormone...

We studied the effects of wheat (Triticum aestivum L.) seed presowing treatment with 0.05 mM salicylic acid (SA) on its endogenous content and the ratio of free to bound forms in seedling shoots and roots. During two-week-long seedling growth, we observed a gradual decrease in the total SA content in shoots but not in roots. In shoots, the content of conjugated SA increased and that of its free form reduced. Seed presowing treatment with SA reduced total content of endogenous SA in both seedling shoots and roots. The content of free SA reduced intensely in shoots and somewhat less in roots. Such reduction was supposed to occur due to the disturbance in SA biosynthesis. These were accompanied by the increases in the shoot and especially root biomass and length, stimulation of total dark respiration, and changes in the ratio between respiratory pathways. In the roots, we observed an increased proportion of cytochrome respiration, whereas in the shoots — alternative cyan-resistant respiration. We also observed changes in the plant antioxidant system. A degree of lipid peroxidation was stronger in shoots than in roots. Pretreatment with SA resulted in MDA 2.5-fold accumulation in shoots, whereas its content in roots reduced by 1.7 times. We concluded that the type and intensity of SA effects on plant growth, energetic balance, and antioxidant status were related to changes in its endogenous content and redistribution between free and conjugated forms.