No abstract

Evaluation of various solvent systems for lipid extraction of wheat Triticum aestivum L. cv. Rideau seeds showed that boiling 2-propanol followed by the Bligh-Dyer procedure was the most efficient method, with respect to lipid yield and ability to inactivate lipolytic enzymes. Ten phospholipids were identified in dry seeds; the major components being phosphatidyleholine, lysophosphatidylcholine, N-acyl lysophosphatidylethanolamine, N-acylphosphatidylethanolamine, and phosphatidylethanolamine. After growth for 1 week (2 C) or 31 hours (24 C), the proportions of phosphatidylethanolamine + lysophosphatidic acid and phosphatidic acid increased, lysophosphatidylcholine decreased, and the remaining phospholipids showed little change. At 5 weeks (2 C) or 72 hours (24 C), the seedlings showed 5-fold increases in the proportion of phosphatidic acid largely at the expense of phosphatidylcholine, small decreases in N-acyl lysophosphatidylethanolamine and N-acylphosphatidylethanolamine, and significant increases in lysophosphatidylcholine. The changes in phosphatidic acid and phosphatidylcholine are interpreted as being partially due to increasing phospholipase D activity during germination. In general, the phospholipid composition was similar in morphologically equivalent seedlings grown at 2 C or 24 C. The increased membrane content in seedlings grown at 2 C does not reflect any preferential synthesis of individual phospholipids.In a previous study (8) seedlings of Triticum aestivum L. cv.Rideau grown at 2 C were found to be more resistant to freezing temperature than their morphological equivalents germinated at 24 C. This resistance was correlated with increased synthesis and unsaturation of cell membrane phospholipids at the lower temperature. Knowledge of the changes in amounts of individual phospholipids in wheat seedlings during germination at both temperatures is required to clarify further the biochemical mechanisms underlying cold-hardiness.The phospholipid composition of wheat seeds has not pre- III. Petroleum ether (b.p. 30-60 C); three 1-hr extractions each with 10 ml of solvent at room temperature (3).IV. Chloroform-methanol-water (1:2:0.8); by the BlighDyer procedure (8). V. Boiling 2-propanol; two extractions each with 5 ml of solvent followed by a Bligh-Dyer extraction (8) of the meal residue; the extracts were combined.VI. Chloroform-methanol (2: 1); four 1-hr extractions with 10 ml of solvent followed by gel filtration on Sephadex G-25 (29).All total lipid extracts were brought to dryness under N2, and the residues were dried in a vacuum desiccator to constant weight, dissolved in 5 ml of chloroform, and aliquots were taken for phosphorus and fatty acid analysis (8).Phospholipid Composition of Seeds. Seeds were imbibed for 5 hr at 24 C, incubated at either 24 C for 31 and 72 hr or at 2 C for 1 and 5 weeks as described elsewhere (8); 2-g lots of seeds were macerated with 0.5 g of silica gel in a mortar with pestle, and total lipids were extracted separately by the methods IV and V. An aliquot of t...

No abstract

No abstract

No abstract

Summary: Résumé: Zusammenfassung Two biotypes of Sorghum halepense (L.) Pers., (Johnson grass) one which overwinters and one which does not overwinter from rhizomes at the northern limit of their North American ranges, were compared for rhizome production, rhizome survival and physiological tolerance to cold. The two biotypes differed in both the amount and depth of rhizome production under field conditions, with the non‐overwintering biotype producing very few rhizomes 20 cm below the soil surface. Rhizome survival was clearly related to depth of burial for both biotypes. Survival was much reduced in the top 20 cm of soil and increased at greater depths to nearly 100% survival at depths of 40 to 50 cm. Differences in rhizome survival were apparent between the two biotypes and under the two climatic conditions tested, with greatly reduced survival of the overwintering biotype in the more extreme northern field plot. Similar levels of cold hardiness were observed in both hardened seedlings and rhizomes of the two biotypes. These levels were low and, in general, would not provide major protection against freezing temperatures. La profondeur des rhizomes; facteur critique de la siurvie hivernale de Sorghum halepense (L.) Pers. (Sorgho d'Alep) Deux biotypes de Sorghum halepense (L.) Pers. (Sorgho d'Alep), l'un capable et l'autre incapable d'hiverner à l'état de rhizomes à la limite septentrionale de leurs aires nord‐américaines, ont été comparés pour leur production en rhizomes, la survie de ces rhizomes et la tolérance physiologique au froid. Les deux biotypes différaient à la fois par la quantité et le niveau de profondeur de leur production de rhizomes au champ :le biotype incapable d'hiverner produisait très peu de rhizomes à une profondeur de 20 cm. La survie des rhizomes était clairement reliée à la profondeur d'enfouissement pour les deux biotypes. La survie était réduite dans les premiers 20 cm de sol et augmentait avec la profondeur jusqu'à presque 100%à des profondeurs de 40 à 50 cm. Des différences de survie des rhizomes étaient apparentes entre les deux biotypes sous les deux conditions climatiques étudiées, le biotype capable d'hiverner présentant un taux de survie fortement réduit dans la parcelle expérimentale située le plus au Nord. Des niveaux similaires d'endurcissement au froid ont été observés dans des plantules et des rhizomes endurcis des deux biotypes. Ces niveaux étaient bas et en général ne fournissaient pas de protection majeure contre le gel. Tiefenlage der Rhizome: der kritische Faktor fur das Ueberleben von Sorghum halepense (L.) Pers. während des Winters Zwei Biotypen von Sorghum halepense (L.) Pers. von der nördlichen Grenze ihres Verbreitungsgebietes in N‐Amerika wurden in Bezug auf Rhizomproduktion, Ueberleben ihrer Rhizome und physiologisch bedingte Kälteresistenz miteinander verglichen. Der eine der beiden Biotype überwintert nicht, der andere überwintert, d.h. reproduziert neues Wachstum aus den bestehen‐den Rhizomen. Die beiden Typen zeigten unter Feldbedingungen Unterschiede in...

The effect of temperature on respiration of mitochondria and tissue segments from three wheat (Triticum aestivum L.) and one rye (Secale cereale L.) cultivar grown at 2 and 24 C has been examined. Discontinuities in Arrhenius plots of respiratory activity against temperature were observed for mitochondria and tissue segments from seedlings grown at both temperatures. The rates of respiration decreased abruptly below the transition temperatures, resulting in increased energy of activation values for respiration. Transition temperatures were observed from 6 to 10 C during tissue segment respiration, and from 10 to 14 C during respiration by isolated mitochondria. Respiratory control and efficiency of phosphorylation were not affected markedly by either reaction temperature or growth temperature of the seedlings. No correlation was observed between the cold hardiness of the cultivars and the temperature at which structural transitions occurred in the mitochondria. Dry matter content of the seedlings increased markedly during growth at 2 C, but no appreciable changes in the levels of mitochondrial protein were observed. The results support the view that changes other than fatty acid unsaturation are involved in the abrupt change in mitochondrial membrane properties at low temperature.Arrhenius plots of the respiration rates of isolated mitochondria show that the apparent energy of activation of respiration increases abruptly with decreasing temperature in mitochondria from chilling-sensitive, but not from chilling-resistant plants (7). Other studies on plant mitochondria (2, 9, 14) also revealed discontnuities in Arrhenius plots of respiration rate and the activity of membrane-bound enzymes. No correlation was observed between the temperature at which the discontinuities occur and the susceptibility of several apple cultivars to chilling injury (9).The observed increase in Ea2 at low temperature is considered due to a temperature-induced change in the lipid component of mitochondrial membranes (13) Recently we examined the structural and functional responses of wheat mitochondrial membranes to growth at low temperature (10). Three possible temperature-dependent structural transitions were identified in the mitochondria by spin labeling and the shift in one of these transitions appeared to be quantitatively greater in the winter-hardy cultivars. Respiration rates, respiratory control, and ADP/O ratios measured at 24 C declined slightly in cold-grown material, but the changes were not related to cold hardiness of the cultivars. This paper describes the effect of reaction temperature on mitochondrial and tissue respiration of three wheat and one rye cultivar of contrasting cold hardiness. MATERIALS AND METHODSSeedlings of wheat (Triticum aestivum L. cv. Kharkov, Cappelle Desprez, and Marquis) and rye (Secale cereale L. cv. Puma) were germinated and grown to the same stage of morphological development on moist filter paper in the dark at 24 and 2 C for approximately 2 days and 4 weeks, respectively. Cold hardin...

The decline in viability of cold-hardy Kharkov winter wheat (Triticum aestivum L.) seedlings during ice encasement at −1 °C was accompanied by characteristic ultrastructural changes. A dramatic increase in endoplasmic reticulum was observed within a few days. This proliferation of endoplasmic reticulum often resulted in the formation of an elaborate series of parallel membranes, either dispersed randomly throughout the cytoplasm or in the form of concentric whorls. However, the structural integrity of many cellular organelles was largely unaffected even by prolonged ice encasement resulting in death of the plants. In contrast, exposure of cold-hardy seedlings to near lethal, subfreezing temperature resulted in severe disorganization of cellular organelles. Ice encasement of nonhardened seedlings resulted in complete kill within 4 h. After 16 h ice encasement, occasional concentric whorls of endoplasmic reticulum and copious amounts of osmiophilic material were observed in the cytoplasm. Upon removal of the ice encasement stress, the accumulated endoplasmic reticulum disappeared rapidly during recovery at either2 or20 °C.