The study of an influence of cold stress on lipid peroxidation at different mitochondrial respiratory chain complexes function in maize mitochondria --Kolesnichenko, AV, Zykova, VV, Grabelnych, OI, Tourchaninova, VV, Voinikov, VK It is known that in plants the development of chilling injury symptoms is frequently coincident with peroxidation of fatty acids (Parkin et al., Food Biochem. 13:127-153, 1989). The source of activated oxygen during freezing stress is not established exactly, but there is experimental evidence to indicate that mitochondria are a major source of superoxide in chilling-sensitive plant tissues at low temperatures (Purvis et al., Physiol. Plant 94:743-749, 1995). It was shown that about 1-2% of oxygen reduced in mitochondria by iron-sulfur centers in complex I and partially by reduced ubiquinone and cytochromes b in complex III is constitutively converted to superoxide, which is a powerful oxidant radical, but, these data were mainly obtained by use of mammalian mitochondria (Chakraborti et al., Cell. Signal 11:77-85, 1999). It is necessary to note that most of the studies of lipid peroxidation during cold stress are concerned with freezing temperatures. Some data on lipid peroxidation at chilling temperatures show that lipoxygenase activity and lipid peroxidation were increased in leaves of maize crops during low temperatures. This suggested that lipoxygenase-mediated peroxidation of membrane lipids contributes to the oxidative damage occurring in chill-stressed leaves (Fryer et al., Plant Physiol. 116:571-580, 1998). Therefore, the present work was aimed at the investigation of an influence of cold stress on lipid peroxidation in maize mitochondria and as a function of different respiratory chain complexes.

The rate of lipid peroxidation was determined by measuring the primary products of lipid peroxidation conjugated diene formation. Mitochondria were incubated in a medium containing 175 mM KCl and 25 mM Tris-HCl (pH 7.4). To determine the lipid peroxidation as a function of different mitochondrial respiratory chain complexes, different substrates were used. Malate was used to study complex I, succinate to study complex II, NADH to study complex III, and ascorbate+TMPD to study complex IV.

The data obtained showed that if electron transfer occurred through complexes I, II or III in mitochondria isolated from non-stressed maize shoots, the rate of lipid peroxidation was equal and rather low (Fig. 1). At complex IV function, the rate of lipid peroxidation was about 50% higher (Fig. 1). These results can be caused by the fact, that at the first two complexes electrons are transferring through the ubiquinone complex, which in plants can function as an effective antioxidant system (Pobezhimova, Voinikov, Membr. Cell Biol., 13:18, 2000).

The study of an influence of low-temperature stress on the rate of lipid peroxidation at different respiratory chain complexes function in mitochondria isolated from stressed (4 C, 1 h) maize shoots showed that low-temperature stress increased dienic conjugates formation associated with function of all respiratory chain complexes. The most pronounced increase (about 75%) was detected for complex IV (Fig. 1).

Thus, based on the data obtained, one can conclude that in maize mitochondria, unlike mammals, the highest lipid peroxidation was associated with complex IV function. Cold stress caused a detectible increase of lipid peroxidation at complexes I, III and especially IV function.

Figure 1. An influence of cold stress (4 C for 1 h) on lipid peroxidation in mitochondria isolated from maize shoots.

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