干旱胁迫下外源水杨酸对黄瓜幼苗膜脂过氧化和光合特性的影响

为了探讨外源水杨酸(SA)提高植物抗旱性的相关机制,研究了干旱胁迫下(基质含水量为饱和持水量的60％和50％),根际施用外源SA对黄瓜幼苗生长、膜脂过氧化、脯氨酸积累、水分利用效率、净光合速率(Pn)和叶绿素荧光参数的影响.结果表明:SA处理能够缓解干旱胁迫对黄瓜幼苗生长、Pn和水分利用效率的抑制,减小膜脂过氧化程度,促进脯氨酸的积累;添加外源SA显著减小了干旱胁迫下黄瓜幼苗的PSⅡ最大光化学效率、PSⅡ实际光化学效率、PSⅡ潜在活性、PSⅡ有效光化学效率和光化学猝灭系数的下降幅度,抑制了非光化学猝灭系数的升高.添加外源SA可以缓解干旱胁迫造成的膜脂过氧化对膜系统的氧化损伤,并通过增强PSⅡ反应中心活性提高了Pn,有助于水分的利用,同时增大渗透调节能力,减少水分的散失,提高水分利用效率,从而增强植株对干旱的适应能力.     

远紫外辐射对紫杉幼苗针叶膜脂过氧化及内源保护系统的影响

实验室条件下用远紫外线(UV-BC)光源照射紫杉幼苗,随照射时间延长,针叶的离子渗出率、膜脂过氧化水平、组织自动氧化速率及H₂O₂含量显著增加,可溶性蛋白、抗坏血酸、类胡萝卜素和叶绿素含量下降,叶绿体光系统II电子传递活性显著下降,外源活性氧清除剂苯甲酸钠和抗坏血酸对针叶膜脂过氧化有抑制作用;甲基紫精和DDC对针叶膜脂过氧化有促进效果,远紫外线引起的紫杉伤害可能和针叶树的越冬光氧化伤害有类似之处.紫杉苗对紫外辐射的抗性远高于一般农作物.     

外源Spd对高温胁迫下黄瓜幼苗叶片膜脂过氧化及质子泵活性的影响

以较为耐热的黄瓜品种‘津春4号’为试材,在人工气候箱中,采用石英砂培养加营养液浇灌的栽培方式,研究了叶面喷施外源亚精胺(Spd)对高温胁迫下黄瓜幼苗叶片膜脂过氧化程度、质子泵活性及其基因表达的影响.结果表明:高温胁迫下,外源Spd促进黄瓜幼苗株高、茎粗、干、鲜质量和叶面积显著增加,有效抑制叶片相对电导率、丙二醛(MDA)含量和脂氧合酶(LOX)活性的升高,有助于提高叶片细胞质膜和液泡膜H+ -ATPase活性,但在基因表达水平上无显著差异.外源Spd可显著降低黄瓜幼苗叶片膜脂过氧化程度,提高质子泵活性,从而稳定膜的结构和功能,缓解高温胁迫对黄瓜幼苗造成的伤害,提高幼苗对高温胁迫的耐性.     

外源多胺对低氧胁迫下黄瓜幼苗光合特性和膜脂过氧化的影响

以抗低氧能力不同的2个黄瓜(Cucumis sativus)品种为试材, 研究了外源多胺对黄瓜幼苗植株生长、光合特性和膜脂过氧化的影响。结果表明, 外源多胺能显著提高低氧胁迫下黄瓜幼苗叶片的净光合速率和水分利用率, 降低叶片中丙二醛含量和质膜透性, 使幼苗鲜重和干重明显增加。因此在低氧胁迫下, 外源喷施多胺能提高幼苗叶片的净光合速率, 促进植株生长, 缓解胁迫对黄瓜幼苗的伤害。此外, 与抗低氧能力较强的品种绿霸春4号相比, 外源多胺对抗低氧能力较弱的品种中农8号的影响更明显。     

外源多胺对低氧胁迫下黄瓜幼苗光合特性和膜脂过氧化的影响

以抗低氧能力不同的2个黄瓜（Cucumis sativus）品种为试材,研究了外源多胺对黄瓜幼苗植株生长、光合特性和膜脂过氧化的影响.结果表明,外源多胺能显著提高低氧胁迫下黄瓜幼苗叶片的净光合速率和水分利用率,降低叶片中丙二醛含量和质膜透性,使幼苗鲜重和干重明显增加.因此在低氧胁迫下,外源喷施多胺能提高幼苗叶片的净光合速率,促进植株生长,缓解胁迫对黄瓜幼苗的伤害.此外,与抗低氧能力较强的品种绿霸春4号相比,外源多胺对抗低氧能力较弱的品种中农8号的影响更明显.     

外源GSH对盐胁迫下水稻叶绿体活性氧清除系统的影响

研究了外源GSH对盐胁迫下耐盐性不同的水稻品种Pokkali(耐盐)和Peta(盐敏感)叶绿体中抗氧化酶活性和抗氧化剂含量的影响.结果表明:盐胁迫下,外源GSH可以提高水稻叶绿体中活性氧清除系统中SOD、APX、GR的活性以及AsA、GSH的含量,降低叶绿体中H2O2和MDA的含量,从而降低了叶绿体膜脂过氧化的水平,缓解盐胁迫对叶绿体膜的伤害.外源GSH对盐胁迫下盐敏感品种Peta叶绿体中上述指标增加或减少的幅度大于耐盐品种Pokkali.     

NaCl胁迫及外源自由基对离体小麦叶片O2^—和膜脂质过氧化的影响…

在ＮａＣｌ胁迫初期,离体小麦叶片内Ｏ２＾－含量较低,随着胁迫时间的延长,自由基产生速率逐渐增加,第４天达最高峰,以后又迅速下降,随着ＮａＣｌ办迫强度增加,叶片内Ｏ２＾－浓度升高,膜脂过氧化作用增强,膜透性增加、ＳＯＤ活性下降,外源自由基处理的叶片中自由基量增加,Ｏ２＾－产生高峰提前,膜脂过氧化作用和膜透性增加。     

豌豆叶绿体脂氧合酶活性与叶片衰老及膜脂过氧化作用的关系

豌豆叶绿体脂氧合酶(LOX)活性在连体叶片衰老过程中变化不大。ABA处理离体叶片2d叶绿体LOX活性升高,处理时间延长活性下降。抗氧化剂α-生育酚、谷胱甘肽、没食子酸丙酯抑制豌豆叶绿体LOX活性。脂质过氧化产物丙二醛对豌豆叶绿体LOX和大豆纯LOX-1的活性均有抑制作用,大豆LOX-1能促进离体豌豆叶绿体膜脂过氧化作用。因此,豌豆叶绿体LOX可能参与叶片衰老过程中叶绿体膜结构和功能的改变,又受膜脂过氧化产物的制约。     

衰老叶片和叶绿体中H_2O_2的累积与膜脂过氧化的关系

在自然衰老和ABA处理的叶片和叶绿体中活性氧H_2O_2均比对照明显增高。外加H_2O_2刺激水稻叶绿体膜脂过氧化作用。叶绿体的丙二醛含量随H_2O_2浓度、光照时间、光照强度及叶绿体完整性而变化。AsA、GSH、SOD、甘露醇和过氧化氢酶对外源H_2O_2引起的膜脂过氧化有缓解作用,Fe~(2+)有刺激作用。而H_2O_2对叶绿体过氧化损伤主要是转化为OH之故。     

NaCl胁迫及外源自由基对离体小麦叶片O_2~和膜脂质过氧化的影响(简报)

在NaCl胁迫初期,离体小麦叶片内O2含量较低,随着胁迫时间的延长,自由基产生速率逐渐增加,第4天达最高峰,以后又迅速下降。随着NaCl胁迫强度增加,叶片内O2浓度升高,膜脂过氧化作用增强,膜透性增加、SOD活性下降。外源自由基处理的叶片中自由基含量增加,O2产生高峰提前,膜脂过氧化作用和膜透性增加。     

Phase Behavior of Chloroplast and Microsomal Membranes during Leaf Senescence

Wide angle x-ray diffraction of chloroplast and microsomal membranes from primary leaves of Phaseolus vulgaris has revealed that for both types of membrane, portions of the lipid become crystalline as the tissue senesces. For young leaves the transition temperature is about 23 C for microsomes and below −30 C for chloroplast membranes, indicating that at physiological temperature the lipid is entirely liquid-crystalline. Between 2 and 3 weeks after planting the transition temperature rises to 38 C for microsomes, but for chloroplasts this increase to a point above physiological temperature does not occur until between 3 and 4 weeks. Thereafter the transition temperature continues to rise for both types of membrane with advancing senescence, although the rate of increase is greater for chloroplasts than for microsomes. The appearance at physiological temperature of gel phase lipid in the microsomes coincides temporally with the initiation of a decline in total protein in the tissue, and the incidence of crystallinity in chloroplasts coincides with loss of chlorophyll. This change in phase behavior cannot be attributed to an alteration in fatty acid composition, but for both membrane systems it correlates with an increase of about 4-fold in the sterol to phospholipid ratio.     

Effects of alpha-tocopherol (vitamin E) on the stability and lipid dynamics of model membranes mimicking the lipid composition of plant chloroplast membranes

Tocopherol (vitamin E) is widely recognized as a cellular antioxidant. It is essential for human and animal health, but only synthesized in photosynthetic organisms, where it is localized in chloroplast membranes. While many studies have investigated non-antioxidative effects of tocopherol on phospholipid membranes, nothing is known about its effects on membranes containing chloroplast glycolipids. Here, liposomes resembling plant chloroplast membranes were used to investigate the effects of alpha-tocopherol on vesicle stability during freezing and on lipid dynamics. alpha-Tocopherol had a pronounced influence on membrane dynamics and showed strong interactions in its effects on membrane stability during freezing with the cryoprotectant sucrose. alpha-Tocopherol showed maximal effects at low concentrations (around 2mol%), close to its contents in chloroplast membranes.     

A role for membrane lipid polyunsaturation in chloroplast biogenesis at low temperature

Two different mutants of Arabidopsis thaliana deficient in chloroplast membrane lipid polyunsaturation were indistinguishable in appearance from the wild-type when grown at 22°C. By contrast, leaf tissues of the mutants that developed during growth at 5°C were chlorotic, whereas the wild type was not. This is the first direct evidence that chloroplast lipid polyunsaturation contributes to low-temperature fitness. Chloroplasts from mutant lines grown at 5°C were much smaller than those of the wild-type, and the thylakoid membrane content was reduced by up to 70%. However, there was no discernible effect of low temperature on chloroplasts that developed prior to exposure to low temperatures. These and related observations suggest that the high degree of chloroplast membrane lipid polyunsaturation is required for some aspect of chloroplast biogenesis.     

Liver microsomal membrane fluidity and lipid characteristics in vitamin A-deficient rats.

Rat liver microsomes (microsomal fraction) were isolated from vitamin A-deficient and -sufficient rats and analysed for membrane lipid characteristics. Membrane fluidity was found to be significantly decreased in microsomes from the vitamin A-deficient rats, but not in liposomes prepared from lipid extracts. Microsomes from vitamin A-deficient animals showed a significant decrease in C18:2, omega 6 and an increase in C22:5, omega 6 fatty acids.     

Altered chloroplast structure and function in a mutant of Arabidopsis deficient in plastid glycerol-3-phosphate acyltransferase activity

Mutants of Arabidopsis thaliana deficient in plastid glycerol-3-phosphate acyltransferase activity have altered chloroplast membrane lipid composition. This caused an increase in the number of regions of appressed membrane per chloroplast and a decrease in the average number of thylakoid membranes in the appressed regions. The net effect was a significant decrease in the ratio of appressed to nonappressed membranes. A comparison of 77 K fluorescence emission spectra of thylakoid membranes from the mutant and wild type indicated that the ultrastructural changes were associated with an altered distribution of excitation energy transfer from antenna chlorophyll to photosystem II and photosystem I in the mutant. The changes in leaf lipid composition did not significantly affect growth or development of the mutant under standard conditions. However, at temperatures above 28°C the mutant grew slightly more rapidly than the wild type, and measurements of temperature-induced fluorescence yield enhancement suggested an increased thermal stability of the photosynthetic apparatus of the mutant. These effects are consistent with other evidence suggesting that membrane lipid composition is an important determinant of chloroplast structure but has relatively minor direct effects on the function of the membrane proteins associated with photosynthetic electron transport.     

Growth temperature effects on thylakoid membrane lipid and protein content of pea chloroplasts

The lipid composition and level of unsaturation of fatty acids has been determined for chloroplast thylakoid membranes isolated from Pisum sativum grown under cold (4°/7°C) or warm (14°/17°C) conditions. Both the relative amounts of lipid classes and degree of saturation were not greatly changed for the two growth conditions. In cold-grown plants, there was a slightly higher linolenic and lower linoleic acid content for the glycolipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol. In contrast to thylakoid membranes, a non-thylakoid leaf membrane fraction including the chloroplast envelope, had a higher overall level of fatty acid unsaturation in cold-grown plants due mainly to an increase in the linolenic acid content of MGDG, DGDG, phosphatidylglycerol, and phosphatidylcholine. The most clear cut change in the thylakoid membrane composition was the lipid to protein ratio which was higher in the cold-grown plants.     

Search for an endotherm in chloroplast lamellar membranes associated with chilling-inhibition of photosynthesis

The phase transition of chloroplast lamellar membrane lipids has been proposed to be the underlying cause of chilling-induced inhibition of photosynthesis in sensitive plants. Differential scanning calorimetry has been used to search for any endotherms arising from lipid state changes in chloroplast lamellar membranes of the chilling-sensitive plants cantaloupe , kidney bean, domestic tomato, and soybean. For comparison, calorimetric scans of chloroplast lamellar membranes from the chilling-insensitive plants spinach, pea, and wild tomato were made. A large reversible endotherm, extending from below 10 degrees to nearly 40 degrees C, was observed in chloroplast membranes from tomatoes of both chilling-sensitive (Lycopersicon esculentum Mill. cv. Floramerica ) and chilling-insensitive (L. hirsutum LA 1361) species. A much smaller endotherm, approximately 5 to 10% of the area of that seen in the two tomato species, and extending over a similar temperature range, was detected in chloroplasts from chilling-insensitive spinach and peas, and also was generally observed in chloroplasts from chilling-sensitive cantaloupe , kidney bean, and soybean. The enthalpy of these smaller endotherms indicates that, if the endotherm arose entirely from a lipid transition, then it corresponded to the melting of less than about 10% of the total membrane polar lipid. On the basis of these data it is concluded that there is no correlation between chilling sensitivity of photosynthesis and the presence or absence of a phase transition of bulk membrane lipids of the chloroplast lamellar membrane at temperatures above 5 degrees C.     

Lipid peroxidation, vitamins C, E and reduced glutathione levels in patients with pulmonary tuberculosis

The present study examined the relationship between lipid peroxidation and vitamin C, vitamin E and reduced glutathione levels in plasma, erythrocytes and erythrocyte membranes of pulmonary tuberculosis patients and an equal number of age-and sex-matched healthy subjects. Enhanced plasma, erythrocytes and erythrocyte membrane lipid peroxidation with concomitant decline in vitamin C, vitamin E and reduced glutathione levels were found in pulmonary tuberculosis patients. The elevated lipid peroxidation and decreased vitamin C, vitamin E and reduced glutathione levels indicate the potential of oxidative damage to erythrocytes and erythrocyte membranes of pulmonary tuberculosis patients.     

Enhanced thermal tolerance in a mutant of Arabidopsis deficient in palmitic Acid unsaturation

A mutant of Arabidopsis thaliana, deficient in the activity of a chloroplast ω9 fatty acid desaturase, accumulates high amounts of palmitic acid (16:0), and exhibits an overall reduction in the level of unsaturation of chloroplast lipids. Under standard conditions the altered membrane lipid composition had only minor effects on growth rate of the mutant, net photosynthetic CO₂ fixation, photosynthetic electron transport, or chloroplast ultrastructure. Similarly, fluorescence polarization measurements indicated that the fluidity of the membranes was not significantly different in the mutant and the wild type. However, at temperatures above 28°C, the mutant grew more rapidly than the wild type suggesting that the altered fatty acid composition enhanced the thermal tolerance of the mutant. Similarly, the chloroplast membranes of the mutant were more resistant than wild type to thermal inactivation of photosynthetic electron transport. These observations lend support to previous suggestions that chloroplast membrane lipid composition may be an important component of the thermal acclimation response observed in many plant species which are photosynthetically active during periods of seasonally variable temperature extremes.     

Tocopherol cyclase (VTE1) localization and vitamin E accumulation in chloroplast plastoglobule lipoprotein particles

Chloroplasts contain lipoprotein particles termed plastoglobules. Plastoglobules are generally believed to have little function beyond lipid storage. Here we report on the identification of plastoglobule proteins using mass spectrometry methods in Arabidopsis thaliana. We demonstrate specific plastoglobule association of members of the plastid lipid-associated proteins/fibrillin family as well as known metabolic enzymes, including the tocopherol cyclase (VTE1), a key enzyme of tocopherol (vitamin E) synthesis. Moreover, comparative analysis of chloroplast membrane fractions shows that plastoglobules are a site of vitamin E accumulation in chloroplasts. Thus, in addition to their lipid storage function, we propose that plastoglobules are metabolically active, taking part in tocopherol synthesis and likely other pathways.