The Mitochondrial Energy-Dissipating Systems (Alternative Oxidase, Uncoupling Proteins and External NADH-Dehydrogenase) are Involved in Frost Resistance Development of Winter Wheat Seedlings
Gene expression, protein synthesis, and activity of alternative oxidase (AOX), uncoupling proteins (pUCP), adenine-nucleotide translocator (ANT), and noncoupled NAD(P)H-dehydrogenases (NDex, NDPex, and NDin) in shoots of etiolated winter wheat (Triticum aestivum L.) seedlings after the action of hardening at low-positive (2°C, 7 days) and freezing (-2°C, 2 days) temperatures have been studied. Cold hardening has been stated to increase the frost-resistance of seedlings and to decrease reactive oxygen species (ROS) generation during further cold shock. Functioning of the mitochondrial energy-dissipating systems may be one of the mechanisms of ROS decrease under these conditions. Participation of the systems in the response to the hardening low-positive and freezing temperatures effects differ. The influence of the first system leads to the induction of AOX and pUCP synthesis, connected with an increase in AOX capacity and increase in non-phosphorylating respiration sensitivity in mitochondria to linoleic and palmitic acids. Increase in the AOX capacity for electron transport after the effect of hardening at freezing temperature to the seedlings is connected with the maintenance of high NDex activity. It is possible that NDex, but not the NDPex and NDin, plays the important role in the maintenance of functional mitochondrial state in heterotrophic plant tissues under the influence of freezing temperatures. We discuss the significance of this finding with regard to the possible physiological role of energy-dissipating systems in mitochondria in adaptation of winter crops to cold and frost.