Structural and Functional Responses of Wheat Mitochondrial Membranes to Growth at Low Temperatures

Abstract

The responses in membrane lipid composition, structure, and function of four cultivars of wheat (Triticum aestivum L.) to growth at Differences in cold tolerance between hardy and nonhardy plant species may reside partially in the ability of the intracellular membranes to adapt to low temperatures (7,10,11,22,23). Mitochondria were selected for a comparison of the structural and functional characteristics of membrane components of four wheat varieties which exhibit quantitatively different degrees of cold hardiness (6,16,19). Since the oxidative and phosphorylative activities of the respiratory membrane may be assessed after growth of seedlings at various temperatures, these activities may be used as intrinsic probes of membrane function. Lyons and Raison (15) indicated that oxidative activity of sweet potato mitochondria declines during storage at 0 C, and that certain phospholipid fractions of the mitochondrial membranes also decrease during cold storage.Structural alterations in the mitochondrial membrane may be inferred from differences in the fatty acid composition of the isolated mitochondrial phospholipids (13). The involvement of membrane lipids in the coupling of the oxidation of substrates with energy conservation and utilization (24) is not completely understood and this fact necessitates further examination of the relationships between lipid composition and membrane structure and function.A more direct physical probe of intact membrane structure has been developed recently (8,17,20). The insertion into the hydrophobic membrane regions of a lipid-soluble probe molecule bearing a nitroxyl-free radical moiety allows assessment of the conditions under which structural changes occur. By recording the electron spin resonance spectra of the nitroxide label over a temperature range, a relative motion parameter, the correlation time, T,, may be determined at the known absolute temperatures. Changes in the slope of Arrhenius plots of T, have been interpreted as indicating phase changes in membrane structure (5). The motion parameter provides a relative measure of molecular restraint within the fluid lipid matrix of the membrane. Correlation of abrupt changes in the temperature dependence of rates of mitochondrial oxidations with changes in the temperature dependence of the molecular motion parameter have been made for plant and animal species (14,15).Studies on the respiratory properties of mitochondria isolated from developing wheat seedlings have indicated that mitochondria with high respiratory rates, and excellent respiratory control and ADP :0 ratios can be obtained from dark-grown 2-to 3-day-old winter wheat seedlings. It has also been shown that these seedlings will develop a high degree of freezing resistance when germinated and grown in the dark at 2 C (4). In winter wheat cultivars, cold resistance is genetically controlled within a species and can be quantitatively measured (6,16,19). Hence, comparisons of the properties of well defined isolated membrane components from tissues grown a...

Swelling and Contraction of Mitochondria from Cold-hardened and Nonhardened Wheat and Rye Seedlings

“…The observation that ca-ketoglutarate in the presence of ADP is oxidized rapidly with good respiratory control and close to theoretical ADP/O ratios (14) suggests that processes other than those normally associated with respiration are involved in mitochondrial contraction. This is supported further by the rapid decline observed in the contraction response when seedlings are grown at 2 C or transferred from 24 to 2 C, although previous studies (11) have demonstrated good respiratory properties of mitochondria isolated from 2 C grown seedlings. These observations may be related to the loss of NADH-induced contraction of mitochondria from drought-stressed corn seedlings (4), since many similarities exist between changes which occur during cold and drought stress.…”

“…A recent study (16) into the effect of temperature on respiration of mitochondria from the same four cultivars grown at 2 and 24 C revealed no correlation between cold hardiness of the cultivars and the transition temperatures for mitochondrial and tissue segment respiration. The observed increase in fatty acid unsaturation of both mitochondrial membranes (11) and total membranes (1) (1,11,15,17), has failed to establish a correlation between cold hardiness and changes in the structural and functional properties of mitochondria and other cell membranes. It has generally been shown that numerous changes occur in the cell which are associated with growth at low temperature but not with the development of cold hardiness.…”

“…Recent studies (11,15) in our laboratories on the mechanism of cold hardening in plants have been directed to investigations of structural and functional properties of wheat and rye mitochondria in relation to growth at low temperature. These studies have revealed a marked increase in the level of fatty acid unsaturation during growth at low temperature, but no differences were observed among cultivars of contrasting cold hardiness.…”

“…Earlier studies on the effect of specific inhibitors of electron transport and oxidative phosphorylation on swelling and contraction (18,20) postulated that high energy intermediates are associated with the active swelling and contraction observed in plant mitochondria. More recent investigations of energized swelling and contraction have led to interpretation of these phenomena in chemiosmotic terms, suggesting that the energy required is derived from changes in the electrochemical proton gradient (2).Recent studies (11,15) in our laboratories on the mechanism of cold hardening in plants have been directed to investigations of structural and functional properties of wheat and rye mitochondria in relation to growth at low temperature. These studies have revealed a marked increase in the level of fatty acid unsaturation during growth at low temperature, but no differences were observed among cultivars of contrasting cold hardiness.…”

Possible Involvement of α-Farnesene in the Development of Chilling Injury in Bananas

“…The development of chilling injury in various tissues has been related to phase changes in the mitochondrial membranes and the degree of unsaturation of the fatty acids of the tissue (3,4,9). Cold-acclimatized wheat plants had increased levels of linolenic acid (6), and a marked decrease in the percentage of unsaturated acids of various chilling-sensitive plants occurred after the plants were exposed to chilling temperatures (13). It has been suggested that the phenomenon of chilling injury cannot be explained entirely by fatty acid composition (6,13).…”