Simulation of the effects of leaf senescence on membranes by treatment with paraquat

Chloroplast and microsomal membranes from the primary leaf of bean acquired increasing proportions of gel phase lipid as the tissue senesced. The lipid-phase transition temperature for microsomes rose from about 25 to 43 C and that for chloroplasts rose from below −30 C to about 52 C within 5 weeks of planting. This was accompanied by large increases (2- to 4-fold) in the sterol to phospholipid ratio of the membranes, which reflected breakdown of phospholipid. Changes in fatty acid saturation were of insufficient magnitude to account for the rise in transition temperature. All of these senescence-related changes in chloroplast and microsomal membranes were also induced by treating young, 2-week-old-plants with 10 milligrams per liter paraquat. Within 48 hours of treatment, the transition temperature rose from 25 to 57 C for microsomes and from below −30 to 24 C for chloroplasts. The membranes sustained only small changes in fatty acid saturation, comparable to those incurred during natural senescence, and there was a selective loss of phospholipid, resulting in augmented sterol to phospholipid ratios. Malondialdehyde, a product of lipid peroxidation, rose by 2- to 3-fold in both senescing and paraquat-treated leaves. Paraquat is known to form cation redicals that react with O₂ to produce O₂⁻ and has been implicated as an agent of lipid peroxidation. Accordingly, these observations suggest that membrane deterioration during natural senescence may be due in part to free radical damage.     

模拟酸雨及其酸化土壤对小麦幼苗膜脂过氧化水平的影响

以小麦为试材,采用盆栽的方法研究了模拟酸雨及其酸化土壤对小麦幼苗膜脂过氧化水平的影响。结果表明以黄棕壤为材料通过模拟酸雨的淋溶,引起了土壤酸化和盐基流失。当模拟酸雨的pH值由5.6下降到2.5时,土壤pH值由6.06下降到3.41,土壤中交换性盐基总量便从56.5mmol/kg下降到41.1mmol/kg。将小麦幼苗栽培在该酸化土壤上,并分别用5种不同pH值的模拟酸雨喷淋地上器官,导致小麦幼苗体内的膜脂过氧化水平增高和保护酶的活性变化。其中模拟酸雨喷淋小麦幼苗对叶片中的膜脂过氧化水平及保护酶活性的影响大于酸化土壤对其产生的影响。而酸化土壤对小麦幼苗根系中的膜脂过氧化水平和保护酶活性的影响大于模拟酸雨喷淋对其产生的影响。同时,pH≤3.0的高强度酸雨以及由其产生的酸化土壤(T4、T5土壤)对小麦幼苗的膜脂过氧化水平和保护酶的活性产生了严重的影响。     

Biochemical changes induced by accelerated aging in sunflower seeds. I. Lipid peroxidation and membrane damage

When stored at 42°C and 100% relative humidity for 1 to 8 days, sunflower seeds (Helianthus annuus L. cv. Rodeo) aged prematurely and lost 25% of their initial viability. A ten-fold increase in conjugated dienes as well as a decrease of unsaturated fatty acids in diacylglycerol and polar lipids fractions were observed after 8 days of accelerated aging, demonstrating the occurrence of lipid peroxidation in prematurely aged sunflower seeds. However, the viability remained relatively high. The absence of membrane damage in seeds and of lipid peroxidation in isolated microsqmes suggested that lipid peroxidation concerned mainly lipid reserves. These results suggest that, at least within the first 8 days of treatment, the lipid reserve in sunflower seeds might act as a detoxifying trap, protecting membranes from excessive damage.     

Induction of gel-phase lipid in plasma membrane of chick intestinal cells after coccidial infection

When chickens are infected with the coccidial parasite Eimeria necatrix, the plasma membrane of intestinal cells harbouring second-generation schizonts becomes refractory to mechanical shearing, hypotonic shock and ultrasonication. Plasma membrane from these infected cells was isolated to high purity as judged by enriched levels of ouabain-sensitive (Na⁺ + K⁺)-stimulated Mg²⁺-dependent ATPase activity and sialic acid content, the lack of detectable cytochrome oxidase and glucose-6-phosphatase activities and electron microscopic analysis of the final preparation. Wide-angle X-ray diffraction patterns recorded from the isolated membranes revealed that during the later stages of parasite maturation the host cell plasma membrane acquires increasing proportions of gel-phase lipid. By contrast, purified membrane from isolated parasites is in a liquid-crystalline state. The transition temperature of host cell plasmalemma at 100 h postinfection is 61°C, about 20°C above physiological temperature. By contrast, liposomes of plasma membranes from infected cells undergo a thermal transition at about 28°C. The accumulation of gel-phase lipid in the host cell plasma membrane is not attributable either to an increase in the constituent ratio of saturated to unsaturated fatty acids or to a significant change in the cholesterol to phospholipid ratio. During the late stages of infection, the cells become stainable with trypan blue which suggests that the acquisition of crystalline phase lipid disrupts the permeability of the host cell plasmalemma.     

Nonesterified fatty acids and lipid peroxidation

Oxygen free radicals damage cells through peroxidation of membrane lipids. Gastrointestinal mucosal membranes were found to be resistant to in vitro lipid peroxidation as judged by malonaldehyde and conjugated diene production and arachidonic acid depletion. The factor responsible for this in this membrane was isolated and chemically characterised as the nonesterified fatty acids (NEFA), specifically monounsaturated fatty acid, oleic acid. Authentic fatty acids when tested in vitro using liver microsomes showed similar inhibition. The possible mechanism by which NEFA inhibit peroxidation is through iron chelation and iron-fatty acid complex is incapable of inducing peroxidation. Free radicals generated independent of iron was found to induce peroxidaton of mucosal membranes. Gastrointestinal mucosal membranes were found to contain unusually large amount of NEFA. Circulating albumin is known to contain NEFA which was found to inhibit iron induced peroxidation whereas fatty acid free albumin did not have any effect. Addition of individual fatty acids to this albumin restored its inhibitory capacity among which monounsaturated fatty acids were more effective. These studies have shown that iron induced lipid peroxidation damage is prevented by the presence of nonesterified fatty acids.     

The role of calcium in improving photosynthesis and related physiological and biochemical attributes of spring wheat subjected to simulated acid rain

The response of photosynthesis parameters, catalase, superoxide dismutase and peroxidase activity, malondialdehyde, proline, chlorophyll, yield and yield components to foliar application of calcium and simulated acid rain in wheat were investigated. Foliar treatment of calcium led to significant increases in the photosynthesis rate, transpiration rate, stomatal conductance, proline, chlorophyll, yield and yield components in plants subjected to acid rain. Antioxidant enzyme activity and lipid peroxidation in the wheat leaves decreased because of calcium foliar application. Calcium hindered degradation of the rubisco subunits under acid rain treatment compared with water-treated plants. Results suggest that acid rain induces the production of free radicals resulting in lipid peroxidation of the cell membrane so that significant increase in antioxidant enzyme activity was observed. In addition, photosynthetic parameters i.e. photosynthesis rate, transpiration rate and stomatal conductance were drastically suppressed by acid rain. The cellular damage caused by free radicals might be reduced or prevented by a protective metabolism including antioxidative enzymes and calcium. We report that foliar application of calcium before acid rain may ameliorate the adverse effects of acid rain in wheat plants.     

An <i>in Vitro</i> Approach to Investigate the Role of Abscisic Acid in Alleviating the Negative Effects of Chilling Stress on Banana Shoots

Banana is a tropical crop cultivated in warm places. Chilling stress in Egypt is making banana crops less productive. Abscisic acid (ABA), a key plant hormone, regulates metabolic and physiological processes and protects plants from a variety of stresses. In vitro growing banana shoots were pre-treated with ABA at four concentrations (0, 25, 50, and 100 mM) and chilled at 5°C for 24 h, followed by a six-day recovery period at 25°C. By comparing ABA treatments to both positive and negative controls, physiological and biochemical changes were investigated. Chilling stress (5°C) caused a considerable increase in lipid peroxidation and ion leakage and reduced photosynthetic pigments in cold-treated plantlets. Increasing the concentration of ABA to 100 µM enhanced the response to chilling stress. ABA had a major effect on mitigating chilling injury in banana shoots by keeping cell membranes stable and lowering the amount of ion leakage and lipid peroxidation. Also, ABA significantly maintained the photosynthetic pigment concentration of banana shoots; accumulated higher amounts of total soluble carbohydrates and proline; and increased DPPH radical scavenging activity. Furthermore, ABA treatment enhanced cold tolerance in chilling-stressed banana shoots through the regulation of antioxidant enzyme activity. Overall, the results show that ABA is a good choice for protecting banana shoots from the damage caused by chilling stress.     

Light-dependence of paraquat-initiated membrane deterioration in bean plants. Evidence for the involvement of superoxide

Treatment of primary bean leaves with 10 mg/I paraquat induces the formation of gel phase lipid in microsomal and chloroplast membranes and enhances the activity of superoxide dismutase, but only if the leaves are exposed to light. These light-dependent changes in membrane lipid phase properties show a close temporal correlation with enhanced O₂⁷ production by illuminated chloroplasts and the onset of lipid peroxidation. Malondialdehyde and ethane, which are both formed during lipid peroxidation, are produced in large amounts by paraquat-treated leaves exposed to light, but not by those maintained in the dark. Electron spin resonance measurements indicate that production of O₂⁷ by illuminated chloroplasts is more than 2-fold greater in the presence of paraquat than in its absence. The identity of the radical formed by illuminated chloroplasts in the presence of paraquat was confirmed by using the diagnostic spin trap 5,5'-dimethyl-l-pyrroline-l-oxide and by establishing that its formation is sensitive to superoxide dismutase. The observations collectively indicate that paraquat-mediated membrane deterioration is light-dependent and attributable to enhanced O₂⁷-production.     

Changes in malondialdehyde content and in superoxide dismutase, catalase and glutathione reductase activities in sunflower seeds as related to deterioration during accelerated aging

Sunflower ( Helianthus annuus L.) seeds progressively lost their ability to germinate at 25°C, the optimal temperature for germination, after accelerated aging was carried out at 45°C (a temperature too high to permit germination) in water or at 76 or 100% relative humidity (RH). The deleterious effects of the high-temperature treatment increased with increasing seed moisture content. Incubation of seeds at 45°C in water resulted in electrolyte leakage, which indicated a loss of membrane integrity. A relationship between leakage and loss of seed viability could not be assumed, since no increase in electrolyte efflux occurred after aging al 100% RH. Accelerated aging induced accumulation of malondialdehyde, suggesting that seed deterioration was associated with lipid peroxidation. However, there was no direct relationship between lipid peroxidation and deterioration in membrane integrity. Loss of seed viability was also associated with a decrease in superoxide dismutase, catalase and glutathione reductase activities. Finally, the results obtained suggest that sunflower seed deterioration during accelerated aging is closely related to a decrease in the activities of detoxifying enzymes and to lipid peroxidation.     

Mitochondrial lipid peroxidation is influenced by dietary factors in early colon carcinogenesis

Oxidative damage to mitochondrial proteins, lipids, and DNA seem to influence the promotion and progression of tumors. High-fat diets and diets high in iron decrease manganese superoxide dismutase activity, a mitochondrial antioxidant, in colon mucosa. Lipid peroxidation products are low in microsomal preparations from colonic mucosa even under peroxide-inducing conditions. However, damage specific to mitochondrial membranes is unknown. This study was designed to investigate dietary lipid and iron effects on fatty acid incorporation and lipid peroxide formation in mitochondrial membranes of colonic mucosa. Male Fischer rats were fed high-fat diets containing either corn oil or menhaden oil with an iron level of either 35 or 535 mg/kg diet. Animals were given two injections of the colon carcinogen, azoxymethane, or saline. Colon tissue was collected 1 and 6 weeks after injections. Mitochondrial and microsomal fractions were prepared for fatty acid analysis and quantitation of lipid peroxidation products. Results showed that lipid composition of both subcellular fractions were influenced by diet. Fatty acid composition of mitochondria differed from microsomes, but overall saturation remained constant. Peroxidation products in mitochondrial membranes were significantly greater than in microsomal membranes. Dietary treatment significantly affected mitochondrial peroxidation in carcinogen-treated animals. Therefore, mitochondria from colon mucosa are more susceptible to peroxidation than are microsomes, dietary factors influence the degree of peroxidation, and the resulting damage may be important in early colon carcinogenesis.     

Contrasting photo- and thermoperiod-induced changes in abscisic acid and lipid contents in leaves of mungbean seedlings

Seedlings of Phaseolus aureus ROXB were grown under 12/12 h light/dark cycles with the light period at 32.5°C and darkness at 10°C (normal conditions N) or with light at 10°C and darkness at 32.5°C (inverse conditions, I). I-conditions affected the level of chlorophyll and carotenoids (very low), monogalactosyldiacylgycerol (low) and phosphatidylinositol (high) in the leaves. Leaves of I-seedlings showed a sharp and durable decline of relative water content during the low temperature phase. For the N-seedlings, loss of water was restricted to the end of this period. The loss of water was accompanied by visible symptoms of wilting at specific times of day. Although the pigment content remained nearly unchanged, ABA content of leaves of both N-and I-seedlings increased during water stress. Upon return to the warm period, ABA level continued to increase after the leaves had regained turgor, this 'after stress'increase being more pronounced in the leaves of I-seedlings. Exogenous application of ABA induced a slight increase in the content of phospholipids in N- and I-leaves and a decrease in free fatty acids, whereas monogalactosyldiacylglycerol content was significantly reduced in N-leaves after application of ABA. Upon transfer of I-plants to 20°C for 12 h during the light period, pigment and chloroplastic lipid content increased rapidly whereas upon a further exposure to 10°C in light, pigments and especially monogalactosyldiacylglycerol were lost. The control of pigment and lipid metabolism and the role of ABA during chilling stress are discussed.     

Effect of Ascorbate on Red Blood Cell Lipid Peroxidation

The present study investigates the effect of ascorbate on red cell lipid peroxidation. At a concentration between 0.2 mmol-20 mmol/l ascorbic acid reduces hydrogen peroxide-induced red blood cell lipid peroxidation resulting in a marked decrease in ethane and pentane production as well as in haemolysis. Ascorbic acid also shows an antioxidant effect on chelated iron-catalyzed hydrogen peroxide-induced peroxidation of erythrocyte membranes. At a concentration of 10 mmol/l ascorbic acid totally inhibits oxidative break-down of polyunsaturated fatty acids by radicals originating from hydrogen peroxide.

Our results indicate that ascorbate at the chosen concentration has an antioxidant effect on red blood cell lipid peroxidation.     

Ultrastructure and lipid alterations induced by cadmium in tomato (Lycopersicon esculentum) chloroplast membranes

The effects of cadmium (Cd) uptake on ultrastructure and lipid composition of chloroplasts were investigated in 28-day-old tomato plants (Lycopersicon esculentum var. Ibiza F1) grown for 10 days in the presence of various concentrations of CdCl2. Different growth parameters, lipid and fatty acid composition, lipid peroxidation, and lipoxygenase activity were measured in the leaves in order to assess the involvement of this metal in the generation of oxidative stress. We first observed that the accumulation of Cd increased with external metal concentration, and was considerably higher in roots than in leaves. Cadmium induced a significant inhibition of growth in both plant organs, as well as a reduction in the chlorophyll and carotenoid contents in the leaves. Ultrastructural investigations revealed that cadmium induced disorganization in leaf structure, essentially marked by a lowered mesophyll cell size, reduced intercellular spaces, as well as severe alterations in chloroplast fine structure, which exhibits disturbed shape and dilation of thylakoid membranes. High cadmium concentrations also affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the fatty acid content and a shift in the composition of fatty acids, resulting in a lower degree of fatty acid unsaturation in chloroplast membranes. The level of lipid peroxides and the activity of lipoxygenase were also significantly enhanced at high Cd concentrations. These biochemical and ultrastructural changes suggest that cadmium, through its effects on membrane structure and composition, induces premature senescence of leaves.     

月季切花衰老过程中多胺与膜脂过氧化的关系

以月季切花为材料,研究了月季切花瓶插过程中多胺含量的变化,外源多胺处理对月季药花体内多胺含量的影响以及多胺与膜脂过氧化的关系。结果表明,月季切花瓶插衰老过程中腐胺在前2d略有增加,亚精胺和精胺均呈下降趋势;外源亚精胺和精胺处理均能增加切花体内多胺含量,并能延缓切花衰老和改善切花品质;且亚精胺和精胺处理降低了MDA含量的积累和膜相对透性的上升趋势。     

外源一氧化氮供体硝普钠对干旱胁迫下小麦幼苗叶中ATP酶活性和膜脂过氧化的影响

研究外源一氧化氮（NO）供体硝普钠（sNP）对干旱胁迫下小麦幼苗叶片ATP酶活性和膜脂过氧化影响的结果表明,15％聚乙二醇．6000（PEG-6000）模拟的干旱胁迫下小麦幼苗叶中H^＋-ATP酶和Ca^2＋．ATP酶活性显著升高后迅速下降,硫代巴比妥酸反应产物（TBARs）和质量膜透性增加;0．1mm01．L^-1 SNP可提高干旱胁迫下小麦幼苗叶中超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（cAT）活性,降低超氧阴离子（O2^-）和过氧化氢（H2O2）水平,缓解膜脂过氧化,稳定生物膜的结构和功能,H^＋-ATP酶和Ca^2＋-ATP酶也可以保持更高的活性。     

Lipid peroxidation in higher plants : the role of glutathione reductase

To study the role of glutathione reductase in lipid peroxidation, bean leaves (Phaseolus vulgaris) cv Fori were treated with the herbicide acifluorfen-sodium (sodium 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid). Acifluorfen is a potent inducer of lipid peroxidation. In beans, decrease of acid-soluble SH-compounds and lipid peroxidation, measured as ethane evolution, were the toxic events after treatment of leaves with acifluorfen. As a primary response to peroxidation, increased production of antioxidants, such as vitamin C and glutathione, was found. This was followed by elevation of glutathione reductase activity. Enhanced activity of the enzyme prevented both further decline of acid-soluble SH-compounds and lipid peroxidation. Increased production of antioxidants and elevated activity of antioxidative enzymes, like glutathione reductase, seem to be a general strategy to limit toxic peroxidation in plants.     

Effect of paclobutrazol and chilling on leaf membrane lipids in cucumber seedlings

The effects of paclobutrazol on the leaf membrane lipid composition of seedlings of cucumber ( Cucumis sativus L. cv. Victory) subjected to chilling temperatures were assessed. At a non-injurious temperature (12.5°C), there was no difference in the polar lipid fatty acid composition or in the glycolipid, phospholipid or free sterol content of leaves from treated vs untreated seedlings, regardless of whether paclobutrazol was administered 1 or 7 days prior to analysis. In the latter case (7 days pretreatment), there were clear effects of the bioregulator on plant growth and morphology as well as on leaf chlorophyll content. At an injurious chilling temperature (5°C), desaturation of leaf polar lipid fatty acids was markedly reduced in both treated and untreated seedlings. Chilling at 5°C resulted in losses of fresh weight and membrane lipids in leaves of both groups of plants. These losses were either reversible or irreversible, depending upon the duration of chilling and of pretreatment with paclobutrazol. Seedlings pretreated with 10 μg ml⁻¹ paclobutrazol generally sustained less chilling injury than untreated controls, as judged by the extent of wilting, necrosis and desiccation. This correlated with reduced losses of leaf fresh Weight and membrane lipids.     

Lipid peroxidation and peroxide-scavenging enzymes associated with accelerated aging of peanut seed

Accelerated aging is known to reduce seed viability and vigor in many crop species. The phenomenon is due in part to aging-induced lipid peroxidation, which has the potential to damage membranes of the seed tissues. This study was undertaken to evaluate the effect of accelerated aging on germinability and several physiological characteristics related to peroxidation in the seed of two peanut cultivars. Accelerated aging was achieved by incubating seed at 45°C and 79% relative humidity in a closed chamber for 3, 6, or 9 days. The results indicate that accelerated aging inhibited seed germination and seedling growth. Enhanced lipid peroxidation and increased peroxide accumulation were observed in the axis and cotyledons of aged seed. Accelerated aging also inhibited the activity of superoxide dismutase, peroxidase, ascorbate peroxidase, and lipoxygenase. Seed axes appeared to be more susceptible to aging than cotyledons. The changes in germination and physiological activities, expressed as a function of aging duration, were similar in the two cultivars, despite differences in their seed weight.     

模拟酸雨对棉花子叶圆片膜保护酶活性和膜脂质过氧化作用的影响

以棉花子叶为材料研究了模拟酸雨对活性氧代谢的影响,发现酸雨使膜保护酶活性下降,膜脂质过氧化作用加强,超氧化物歧化酶在控制子叶膜脂质过氧化中起重要作用。自由基清除剂(FRS)的应用能有效地抑制伤害子叶膜脂质过氧化作用,并有利于保持较高的膜保护酶活性和维持活性氧代谢平衡。     

Cadmium effects on lipid metabolism of rape (Brassica napus L.)

Treatment of rape seedlings with increasing CdCl₂ concentrations in the culture medium resulted in a cadmium accumulation within plant tissues, which increased with external metal dose; such accumulation was more important in roots than in leaves. Biomass production was severely inhibited, even at low cadmium concentration. In leaves, quantities of chloroplastic lipids, monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfolipids (SL) and phosphatidylglycerol (PG) decreased sharply under metallic treatment. However, contents of extrachloroplastic lipids, mainly phosphatidylcholine (PC) and phosphatidylethanolamine (PE) increased significantly. In contrast to leaves, contents of root phospholipids decreased. Likewise, levels of tri-unsaturated fatty acids: linolenic (C18:3) and hexadecatrienoïc (C16:3) dropped in leaves of treated seedlings as compared to those of controls, suggesting that heavy metals induced an alteration in the fatty acid desaturation process or a stimulation of their peroxidation. Also, trans palmitoleic acid (C16:1-trans) level in PG decreased considerably. In roots, there was a slight decrease in C18:3 level, with a concomitant increase in the C18:2 percentage. Radioactive labelling of leaf lipids with (1-¹⁴C) acetate allowed to show that fatty acid biosynthesis was noticeably altered at the highest cadmium dose used (50 μM). Biosynthesis of tri-unsaturated fatty acids was also inhibited which may explain the decline in non-labelled lipid contents. Results showed that metallic ion seems to affect selectively chloroplastic membranes due to an inhibition of polyunsaturated fatty acid biosynthesis. Moreover, a lipid peroxidation occurred in our case because of the spectacular increase of malondialdehyde (MDA) content observed in cadmium treated leaves. To cite this article: N. Ben Youssef et al., C. R. Biologies 328 (2005).