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Most seeds are anhydrobiotes, relying on an array of protective and repair mechanisms, and seed mitochondria have previously been shown to harbor stress proteins probably involved in desiccation tolerance. Since temperature stress is a major issue for germinating seeds, the temperature response of pea (Pisum sativum) seed mitochondria was examined in comparison with that of mitochondria from etiolated epicotyl, a desiccation-sensitive tissue. The functional analysis illustrated the remarkable temperature tolerance of seed mitochondria in response to both cold and heat stress. The mitochondria maintained a well-coupled respiration between 23.5°C and 40°C, while epicotyl mitochondria were not efficient below 0°C and collapsed above 30°C. Both mitochondria exhibited a similar Arrhenius break temperature at 7°C, although they differed in phospholipid composition. Seed mitochondria had a lower phosphatidylethanolamine-to-phosphatidylcholine ratio, fewer unsaturated fatty acids, and appeared less susceptible to lipid peroxidation. They also accumulated large amounts of heat shock protein HSP22 and late-embryogenesis abundant protein PsLEAm. The combination of membrane composition and stress protein accumulation required for desiccation tolerance is expected to lead to an unusually wide temperature tolerance, contributing to the fitness of germinating seeds in adverse conditions. The unique oxidation of external NADH at low temperatures found with several types of mitochondria may play a central role in maintaining energy homeostasis during cold shock, a situation often encountered by sessile and ectothermic higher plants.Many organisms need to cope with extreme temperatures, but few are adapted to live and reproduce in such conditions. While extremophilic microorganisms can metabolically adapt, more complex organisms avoid temperature stress by controlling body temperature or by moving to more favorable habitats. As land plants are ectothermic and unable to move, they cannot escape dramatic changes in temperature. Most live in environments where frequent temperature changes of 10°C to 20°C are common, and some, such as alpine plants, may experience fluctuations of more than 40°C in a single day. While much work has been carried out on the acclimation of plants to either low or high temperature, little is known about the mechanisms allowing them to cope with sudden temperature fluctuations that may exist for extended periods. In analyzing this situation, we obtained evidence from seeds that mitochondria play a central role in allowing plants to adapt to extreme temperatures.In the life cycle of higher plants, seeds must complete the crucial task of protecting the embryo and driving it toward the establishment of a new generation. The majority of higher plant seeds are desiccation tolerant, a complex trait that has contributed to the evolutionary success of angiosperms. Desiccationtolerant seeds are in fact anhydrobiotes and certainly represent the most stress-tolerant stage of plants. They are endowed with an impressiv...

SummaryApart from energy generation, mitochondria perform a signalling function determining the life and death of a cell under stress exposure. In the present study we have explored patterns of heat-induced synthesis of Hsp101, Hsp70, Hsp17.6 (class I), Hsp17.6 (class II) and Hsp60, and the development of induced thermotolerance in Arabidopsis thaliana cell culture under conditions of mitochondrial dysfunction. It was shown that treatment by mitochondrial inhibitors and uncouplers at the time of mild heat shock downregulates HSP synthesis, which is important for induced thermotolerance in plants. The exposure to elevated temperature induced an increase in cell oxygen consumption and hyperpolarization of the inner mitochondrial membrane. Taken together, these facts suggest that mitochondrial functions are essential for heat-induced HSP synthesis and development of induced thermotolerance in A. thaliana cell culture, suggesting that mitochondrialnuclear cross-talk is activated under stress conditions. Treatment of Arabidopsis cell culture at 50°C initiates a programmed cell death determined by the time course of viability decrease, DNA fragmentation and cytochrome c release from mitochondria. As treatment at 37°C protected Arabidopsis cells from heat-induced cell death, it may be suggested that Hsp101, Hsp70 and small heat-shock proteins, the synthesis of which is induced under these conditions, are playing an anti-apoptotic role in the plant cell. On the other hand, drastic heat shock upregulated mitochondrial Hsp60 synthesis and induced its release from mitochondria to the cytosol, indicating a pro-apoptotic role of plant Hsp60.

Background: Dehydrins are known as Group II late embryogenesis abundant proteins. Their high hydrophilicity and thermostability suggest that they may be structure stabilizers with detergent and chaperone-like properties. They are localised in the nucleus, cytoplasm, and plasma membrane. We have recently found putative dehydrins in the mitochondria of some cereals in response to cold. It is not known whether dehydrin-like proteins accumulate in plant mitochondria in response to stimuli other than cold stress.

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