Late-embryogenesis abundant (LEA) proteins are hydrophilic proteins that accumulate to a high level in desiccation-tolerant tissues and are thus prominent in seeds. They are expected to play a protective role during dehydration; however, functional evidence is scarce. We identified a LEA protein of group 3 (PsLEAm) that was localized within the matrix space of pea (Pisum sativum) seed mitochondria. PsLEAm revealed typical LEA features such as high hydrophilicity and repeated motifs, except for the N-terminal transit peptide. Most of the highly charged protein was predicted to fold into amphiphilic a-helixes. PsLEAm was expressed during late seed development and remained in the dry seed and throughout germination. Application of the stress hormone abscisic acid was found to reinduce the expression of PsLEAm transcripts during germination. PsLEAm could not be detected in vegetative tissues; however, its expression could be reinduced in leaves by severe water stress. The recombinant PsLEAm was shown to protect two mitochondrial matrix enzymes, fumarase and rhodanese, during drying in an in vitro assay. The overall results constitute, to our knowledge, the first characterization of a LEA protein in mitochondria and experimental evidence for a beneficial role of a LEA protein with respect to proteins during desiccation.Late-embryogenesis abundant (LEA) proteins are overwhelmingly hydrophilic proteins that accumulate to high levels in the latter stages of seed maturation and disappear following germination (Galau et al., 1986). While almost ubiquitous in the plant kingdom, data mining has revealed the widespread occurrence of LEA proteins in prokaryotes and eucaryotes (GarayArroyo et al., 2000). Historically clustered in five main groups based on primary structure analysis (Dure et al., 1989;Cuming, 1999), the LEA protein classification was recently reexamined using statistically based bioinformatic tools (Wise, 2003).LEA protein expression, which often appears abscisic acid (ABA) dependent, can also occur in vegetative tissues subjected to water deficit associated with drought, salt, or cold stress (for review, see Ingram and Bartels, 1996;Thomashow, 1998;Cuming, 1999). Both the pattern of expression and the structural features of LEA proteins suggest a general protective role in desiccation tolerance (Ingram and Bartels, 1996;Cuming, 1999). This hypothesis was recently supported by the discovery of a LEA protein in an anhydrobiotic nematode (Browne et al., 2002) as well as by the sensitization to desiccation induced by mutational inactivation of LEA genes in the prokaryote Deinococcus radiodurans (Battista et al., 2001). In view of the apparent lack of well-ordered tertiary structure of LEA proteins preventing their use as catalysts, several mechanisms have been proposed to relate their structural features to the protection of cellular structures required by a dehydrated state: water replacement, ion sequestering, macromolecules, and membrane stabilization (Close, 1996(Close, , 1997Cuming, 1999). Experimentally, sev...

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...

This chapter discusses the results of studies on mitochondrial functions during the germination of legume seeds, using pea (cv. Baccara) as the initial material. Mitochondrial integrity and oxidative properties were observed to improve during imbibition of pea seeds, with energy transduction relying mainly on cytosol NADH and succinate oxidation.