低温锻炼后桑树幼苗光合作用和抗氧化酶对冷胁迫的响应

以桑树品种“秋雨”为试验材料,研究了桑树幼苗在低温锻炼、冷胁迫和常温恢复期间的光合作用和抗氧化酶活性的变化.结果表明: 12 ℃3 d低温锻炼明显提高了桑树幼苗的抗冷性.3 ℃3 d冷胁迫下,12 ℃3 d低温锻炼后的桑树幼苗叶片净光合速率(P_n)、气孔导度(G_s)和PSⅡ 最大光化学效率(F_v/F_m)明显高于对照(未经低温锻炼)处理的桑树幼苗,而且其在常温下的恢复也较对照桑树幼苗迅速.在12 ℃ 3 d低温锻炼和3 ℃ 3 d冷胁迫期间,桑树幼苗叶片脯氨酸和可溶性糖含量明显增加,而经低温锻炼的桑树幼苗叶片丙二醛(MDA)含量明显低于未经低温锻炼的桑树幼苗,经低温锻炼的桑树幼苗叶片抗坏血酸过氧化物酶(APX)活性则明显高于未经低温锻炼的桑树幼苗.说明渗透调节物质含量增加和APX活性提高在低温锻炼诱导桑树幼苗的抗冷性上发挥着重要的作用.     

低温胁迫下烤烟幼苗叶片光合作用和抗氧化能力基因差异表达谱

对低温(5—7℃)胁迫下烤烟"K326"幼苗叶片光合指标、膜氧化水平及其抗氧化指标进行测定,并利用数字化基因表达谱技术进行基因差异表达分析。低温胁迫后烤烟幼苗叶绿素含量、光合能力显著下降,脯氨酸含量、丙二醛含量上升,超氧化物歧化酶活性、过氧化氢酶活性、抗坏血酸含量和谷胱甘肽含量均显著上升。低温胁迫后有2357个基因发生了显著差异表达,其中1673个基因表达上调、684个基因表达下调,其分子功能、细胞位置和主要代谢过程均涉及光系统、膜氧化系统和抗氧化系统。对涉及到的代谢过程进行分析,结果表明:光合天线蛋白调控基因表达量均显著下降、光合作用的主要调控基因表达量多数表现为显著下调、而与氧化能力相关的谷胱甘肽代谢差异表达基因大多数显著上调。基因差异表达谱分析结果和低温胁迫后叶片光合能力、抗氧化能力生理生态指标测定结果基本一致,为进一步研究低温胁迫对作物的生态影响和研究基因克隆与功能提供基础。     

Response of xanthophyll cycle and chloroplastic antioxidant enzymes to chilling stress in tomato over-expressing glycerol-3-phosphate acyltransferase gene

Over-expression of chloroplastic glycerol-3-phosphate acyltransferase gene (LeGPAT) increased unsaturated fatty acid contents in phosphatidylglycerol (PG) of thylakoid membrane in tomato. The effect of this increase on the xanthophyll cycle and chloroplast antioxidant enzymes was examined by comparing wild type (WT) tomato with the transgenic (TG) lines at chilling temperature (4 °C) under low irradiance (100 μmol m⁻² s⁻¹). Net photosynthetic rate and the maximal photochemical efficiency of photosystem (PS) 2 (F_v/F_m) in TG plants decreased more slowly during chilling stress and F_v/F_m recovered faster than that in WT plants under optimal conditions. The oxidizable P700 in both WT and TG plants decreased during chilling stress under low irradiance, but recovered faster in TG plants than in the WT ones. During chilling stress, non-photochemical quenching (NPQ) and the de-epoxidized ratio of xanthophyll cycle in WT plants were lower than those of TG tomatoes. The higher activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in TG plants resulted in the reduction of O₂ ^−· and H₂O₂ contents during chilling stress. Hence the increase in content of unsaturated fatty acids in PG by the over-expression of LeGPAT could alleviate photoinhibition of PS2 and PS1 by improving the de-epoxidized ratio of xanthophyll cycle and activities of SOD and APX in chloroplast.     

Enhanced tolerance to oxidative stress in transgenic tobacco plants expressing three antioxidant enzymes in chloroplasts

The effect of simultaneous expression of genes encoding three antioxidant enzymes, copper zinc superoxide dismutase (CuZnSOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), and dehydroascorbate (DHA) reductase (DHAR, EC 1.8.5.1), in the chloroplasts of tobacco plants was investigated under oxidative stress conditions. In previous studies, transgenic tobacco plants expressing both CuZnSOD and APX in chloroplast (CA plants), or DHAR in chloroplast showed enhanced tolerance to oxidative stresses, such as paraquat and salt. In this study, in order to develop transgenic plants that were more resistant to oxidative stress, we introduced the gene encoding DHAR into CA transgenic plants. Mature leaves of transgenic plants expressing all three antioxidant genes (CAD plants) had approximately 1.6–2.1 times higher DHAR activity, and higher ratios of reduced ascorbate (AsA) to DHA, and oxidized glutathione (GSSG) to reduced glutathione (GSH) compared to CA plants. CAD plants were more resistant to paraquat-induced stress, exhibiting only 18.1% reduction in membrane damage relative to CA plants. In addition, seedlings of CAD plants had enhanced tolerance to NaCI (100 mM) compared to CA plants. These results indicate that the simultaneous expression of multiple antioxidant enzymes, such as CuZnSOD, APX, and DHAR, in chloroplasts is more effective than single or double expression for developing transgenic plants with enhanced tolerance to multiple environmental stresses.     

Responses to chilling stress in French bean seedlings: antioxidant compounds

French bean (Phaseolus vulgaris L. cv. Contender) plants at five developmental stages (4, 8, 12, 16 and 20 d after sowing) were exposed to one of three treatments: 1 - 25 °C (control), 2 - exposure to chilling at 10 °C only for 2 d prior to sampling, and 3 - long-term exposure to chilling at 10 °C. Short- and long-term chilling decreased plant growth. Higher concentrations of ascorbate and glutathione were found in the chilling-treated plants throughout the different period of growth in comparison with those in the control plants. The activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase increased in the chilling-treated seedlings while activities of catalase and peroxidase and of β-carotene content decreased in young chilling-treated plants and slightly increased in older ones. This revised version was published online in July 2006 with corrections to the Cover Date.     

Overexpression of tomato GDP-l-galactose phosphorylase gene in tobacco improves tolerance to chilling stress

Key message

The overexpression of tomato GDP- l -galactose phosphorylase gene enhanced tolerance to chilling stress and reduced photoinhibition of photosystems I and II in transgenic tobacco.

Abstract

Chilling stress is a crucial factor that limits the geographical distribution and yield of chilling-sensitive plants. Ascorbate (AsA) protects plants by scavenging reactive oxygen species and reduces photoinhibition by promoting the conversion of violaxanthin to zeaxanthin in the xanthophyll cycle to dissipate excess excitation energy. Possible mechanisms of AsA for plant photoprotection under chilling stress were investigated by isolating the tomato GDP-l-galactose phosphorylase gene (SlGGP) and producing transgenic tobacco plants with overexpression of SlGGP. The transgenic plants subjected to chilling stress accumulated less H₂O₂, demonstrated lower levels of ion leakage and malondialdehyde, and acquired higher net photosynthetic rate, higher maximum photochemical efficiency of PSII, and higher D1 protein content compared with the wild-type (WT) plants. The transgenic plants subjected to chilling stress also showed higher GDP-l-galactose phosphorylase activity, increased AsA content as well as ascorbate peroxidase and oxidizable P700 activities than WT plants. Thus, SlGGP overexpression is crucial in promoting AsA synthesis and alleviating photoinhibition of two photosystems.     

Different responses of photosystem I and photosystem II in three tropical oilseed crops exposed to chilling stress and subsequent recovery

Key message

Different responses of photosystem I and II to chilling.

Abstract

Tropical crops are sensitive to chilling stress, but the underlying physiological mechanisms are unclear. We investigated the maximum quantum yield of PSII (F _v/F _m), the maximum photo-oxidizable P700 (P _m), the energy distribution in PSII, and the redox state of P700 in leaves of seedlings of three promising oilseed crops originating from tropical regions, Plukenetia volubilis, Jatropha curcas and Ricinus communis, during chilling treatment and subsequent recovery under a photon flux density of 450 μmol m^?2 s^?1. Our results showed that F _v/F _m decreased progressively and significantly to about 44.7, 62.2 and 77.0 % of the control after chilling treatment for 3 days in P. volubilis, J. curcas and R. communis, respectively, mainly due to the decrease in F _m (maximum fluorescence of PSII). After recovery under 18 °C for 6 days, F _v/F _m recovered to 81.4 and 94.9 % of the control in J. curcas and R. communis, but only to 26.3 % in P. volubilis. Under chilling stress and subsequent recovery, P _m remained stable in J. curcas and R. communis, whereas it decreased slightly in P. volubilis. These results indicated that PSII was more sensitive to chilling stress than PSI under moderate light for all three species, and that P. volubilis was the most susceptible. Cyclic electron flow around PSI and effective quantum yield of photosystem II [Y _(CEF)/Y _(II)] ratio were stimulated much more in J. curcas and R. communis compared with that in P. volubilis under chilling conditions, resulting in more severe injury as indicated by higher accumulation of hydrogen peroxide and malondialdehyde. There was a significantly negative relationship between F _v/F _m and Y _(CEF)/Y _(II), suggesting that stimulation of Y _(CEF)/Y _(II) plays a pivotal role in protecting PSI and PSII from photoinhibition caused by chilling stress.     

Different photosynthetic responses to night chilling among twelve populations of Jatropha curcas

Jatropha curcas, one of the most important energy plant resources, is vulnerable to chilling. To evaluate the effects of chilling on photosynthesis of J. curcas and intraspecific differences in chilling tolerance, seedlings of twelve populations were treated with the temperature of 4–6°C for five consecutive nights with normal environmental temperature during the day. Night chilling treatment decreased light-saturated photosynthetic rate (P _max) significantly for all populations. Stomatal limitation could not explain the decreased P _max because intracellular CO₂ concentration was not significantly reduced by night chilling in all populations (with only one exception). The decreased soluble-protein content, which may be related to the increased malondialdehyde (MDA) content, contributed to the decreased P _max. The increased MDA content indicated that oxidative stress occurred after night chilling, which was associated with the larger decrease in P _max compared with the decrease in actual photochemical efficiency of photosystem II, and the slight increase in thermal dissipation of excessive energy. After five-day recovery, MDA (with two exceptions) and P _max still did not recover to the levels as those before night chilling treatment for all populations, indicating that J. curcas was vulnerable to chilling. Chilling tolerance was significantly different among populations. Populations originating from high elevations had greater chilling-tolerant abilities than populations originating from low elevations, showing a local adaptation to environmental temperatures of origins. Our study shed light on the possibility to find or breed chilling-tolerant genotypes of J. curcas.     

低温逆境对不同核桃品种抗氧化系统及超微结构的影响

为揭示核桃抗寒机理,确定核桃抗寒性鉴定适宜的生化指标,以展叶期抗寒性不同的哈特雷、晋龙1号和晋龙2号3个品种1年生枝条的叶片为材料,测定了1℃低温下抗氧化酶活性及超氧阴离子(O2(-))含量的变化,并采用透射电子显微镜观察低温逆境对抗寒性差异大的哈特雷和晋龙2号叶肉细胞超微结构的影响.结果表明:低温胁迫前后抗寒性强的哈特雷叶片中超氧化物歧化酶(SOD)和过氧化物酶(POD)的活性最高,超氧阴离子含量最低,叶肉细胞超微结构较稳定,叶片没有明显冷害症状.抗寒性差的晋龙2号随着低温胁迫时间的延长,3种抗氧化酶活性的下降幅度最大,O2(-)含量始终处于高水平;胁迫72 h时细胞叶绿体普遍膨胀,基粒片层变薄,数目减少,部分叶绿体被膜及质膜清晰度下降,部分顶端小叶叶缘呈水浸状,表现出冷害症状.可见,低温逆境下核桃叶肉细胞超微结构的稳定性与其品种的抗寒性密切相关.SOD、POD活性以及O2(-)含量可作为展叶期核桃抗寒性鉴定的生化指标;低温胁迫下核桃叶片细胞内膜系统的损伤与活性氧积累之间可能存在一定的相互关系.     

Antioxidant enzyme responses to chilling stress in differentially sensitive inbred maize lines

Antioxidant enzyme activities were determined at the first,third and fifth leaf stages of four inbred lines of maize (Zeamays L.) exhibiting differential sensitivity to chilling. Plantswere exposed to a photoperiod of 16:8 L:D for one of three treatments:(a) control (25C), (b) control treatment plus an exposure toa short-term chilling shock (11C 1 d prior to harvesting),and (c) long-term (11 C constant) chilling exposure. Catalase(CAT; EC 1.11.1.6 [EC] ), ascorbate peroxidase (ASPX; EC 1.11.1.11 [EC] ),superoxide dismutase (SOD; EC 1.15.1.1 [EC] ), glutathione reductase(GR; EC 1.6.4.2 [EC] ), and mono-dehydroascorbate reductase (MDHAR;EC 1.6.5.4 [EC] ) activities were assessed. Reducing and non-reducingsugars and starch concentrations were determined as generalmetabolic indicators of stress. Reduced activities of CAT, ASPX,and MDHAR may contribute to limiting chilling tolerance at theearly stages of development in maize. Changes in levels of sugarand starch indicated a more rapid disruption of carbohydrateutilization in comparison to photosynthetic rates in the chilling-sensitiveline under short-term chilling shocks and suggested a greaterdegree of acclimation in the tolerant lines over longer periodsof chilling. Key words: Antioxidant enzymes, differential chilling sensitivity, maize, soluble carbohydrates, Zea mays     

Antioxidant compound responses to chilling stress in differentially sensitive inbred maize lines

Chilling temperatures increase the amounts of potentially lethal toxic oxygen compounds present within plants. These toxic oxygen compounds can be scavenged by antioxidant compounds such as ascorbate and β-carotene. Three developmental stages (first, third and fifth leaf) of four inbred lines of maize ( Zea mays L.) exhibiting differential sensitivity to chilling were examined in order to determine if the chilling-sensitive line had lower concentrations of antioxidant compounds than did the tolerant lines. Plants were exposed to one of three treatments: (1) control (25°C constant), (2) control treatment plus a short-term chilling exposure of 11°C one day prior to harvesting, and (3) long-term (11°C constant) chilling exposure. Total ascorbate, total glutathione, β-carotene, α-tocopherol and chlorophyll contents were quantified, and ratios of dehydroascorbate/ascorbate and reduced/oxidized glutathione were determined. Lower concentrations of β-carotene were found in the chilling-sensitive relative to those in the chilling-tolerant lines for the first-leaf stage under both short- and long-term chilling treatments. Concentrations of total ascorbate and glutathione and β-carotene in the chilling-sensitive line increased as the chilling treatment progressed and as the plants developed until they ultimately became either significantly higher or no different relative to the tolerant lines. Results suggest that this sensitive line became less sensitive to chilling-induced oxidative stress with development.     

Recovery of maize (Zea mays L.) inbreds and hybrids from chilling stress of various duration: photosynthesis and antioxidant enzymes

The differences between two maize (Zea mays L.) inbred lines and their F1 hybrids in their response to chilling periods of various duration (1, 2, 3 or 4 weeks) and subsequent return to optimum temperatures were analysed by the measurement of the photosystem (PS) 1 and 2 activity, the photosynthetic pigments' content and the activity of antioxidant enzymes. The PS2 activity and the chlorophyll content decreased in plants subjected to 3 or 4 weeks of chilling, but not in those subjected to 1 or 2 weeks of chilling. This decrease was more pronounced in inbreds compared to their hybrids. The activity of superoxide dismutase did not much change with the increasing length of chilling period in the inbreds but decreased in the hybrids, the glutathione reductase activity increased in both types of genotypes but more in the inbred lines, while for ascorbate peroxidase and catalase the changes in parents-hybrids relationship did not show any specific trend. The PS1 activity and the carotenoids' content was not much affected.     

Effect of exogenous H2O2 on antioxidant enzymes of Brassica juncea L. seedlings in relation to 24-epibrassinolide under chilling stress

Hydrogen peroxide is most stable molecule among reactive oxygen species, which play a vital role in growth and development of plant as signaling molecule at low concentration in response to various abiotic and biotic stresses. Exogenous application of H2O2 is known to induce chilling tolerance in plants. Brassinosteroids are plant steroid hormones known for their anti-stress properties. In this study, effect of exogenous H2O2 on antioxidant defense system of Brassica juncea L. seedlings was investigated in 24-epibrassinolide (24-EBL) treated and untreated seedlings under chilling stress. The surface sterilized seeds of B. juncea L. were germinated in petriplates containing different concentrations of H2O2 alone and in combination with 10(-8) M 24-EBL. Chilling treatment (4 degrees C) was given to 10-days old seedlings grown in different treatments for 6 h daily up to 3 days. 24 h recovery period was given to chilling treated seedlings by placing at 25 degrees C + 2 degrees C and harvested for antioxidant enzymes on 14th day after sowing (DAS). Treatment of 24-EBL in combination with H2O2 (15 and 20 mM) helped in reducing the toxicity of seed and seedlings due to H2O2 exposure on their germination rate, shoot and root length respectively. 24-EBL treatment at seed and seedling stage helped in alleviating the toxic effect of H2O2 through antioxidant defense system by increasing the activities of various enzymes involved in antioxidant defense system such as catalase (CAT, E.C. 1.11.1.6), ascorbate peroxidase (APOX, E.C. 1.11.1.11), and superoxide dismutase (SOD, E.C. 1.15.1.1). In conclusion, exogenous pretreatment of H2O2 to seeds of B. juncea L. adapted the seedlings to tolerate chilling stress, which was further ameliorated in combination of H2O2 with 24-EBL.     

Effect of chilling on photosynthesis and antioxidant enzymes in Hevea brasiliensis Muell. Arg.

The aim of the present study was to assess the tolerance of Hevea brasiliensis to chilling temperatures since rubber production has been extended to sub-optimal environments. PB260 clone was used to analyze the responses of leaves chilled at 10°C during 96 h, as well as their recovery at 28°C. Some key parameters were used to evaluate photosynthetic apparatus functioning, membrane damage (electrolyte leakage) and oxidative stress. A short-term response versus a long-term one have been recorded, the time point of 24 h, when stomata closure was effective, being the border between the two responses. P _n decreased dramatically at 1 h, and Fv/Fm was slightly affected. NPQ reached its maximal level between 4 and 7 h. Lipid peroxidation and membrane lysis were observed between 48 and 96 h. Activities of antioxidant enzymes increased, along with the induction of antioxidant gene expression. Finally, the plants were capable to recover (net photosynthetic rate, photochemical efficiency, antioxidant enzymes activities) when placed back to 28°C showing that PB260 can withstand long-term chilling.     

Various aspects of inhibition of photosynthesis under light/chilling stress: “Photoinhibition at chilling temperatures” versus “chilling damage in the light”

At chilling temperatures, plants suffer damage to photosynthesis. The sites and the mechanisms involved in this damage differ under different chilling conditions. The current status of our understanding of this damage is reviewed, and how chilling temperatures affect photosynthesis is discussed with emphasis on the role of light and the phase separation of membrane lipids. Recipient of the Botanical Society Award for Young Scientist, 1996     

Physio-anatomical responses of tobacco under caffeine stress

Caffeine, a purine alkaloid, is reported to act both as an inducer or inhibitor to plant growth in various species. The aim of this study was to examine the effect of exogenous caffeine on tobacco (Nicotiana tabacum) plants, a plant that does not naturally synthesise caffeine. A hydroponic experiment was carried out in a growth chamber for 14 d using Hoagland’s solution supplemented with 0 (control), 25, 50, 100, 1,000; and 5,000 μM caffeine. None of the investigated caffeine concentrations significantly decreased the net photosynthetic rate except the highest concentrations of 1,000 and 5,000 μM. Light microscopy of thick-sectioned roots showed that 1,000 μM and 5,000 μM caffeine-treated plants possessed deformed epidermal cells, reduced number of cortical cells, and deformed vascular tissues with cells exhibiting thickened xylem walls as compared with control plants. Moreover, transmission electron micrographs of roots revealed that mitochondria and the plasma membrane were affected.     

Effect of stress on the antioxidant enzymes and gastric ulceration

The effect of cold-restraint stress on the antioxidant enzymes of the rat gastric mucosa was studied with a view to finding out their role in stress induced gastric ulceration. Histological examination revealed stress induced extensive damage of the surface epithelial cell with lesions extending upto submucosa in some cases. Stress causes time-dependent increase in histamine and pepsin content but decrease in acid content of the gastric fluid with the progress of ulceration (ulcer index) for two hours. The tissue lipid peroxidation was significantly increased as evidenced by accumulation of malondialdehyde. Since lipid peroxidation results from the generation of reactive oxygen species, stress effect was studied on some antioxidant enzymes such as superoxide dismutase, peroxidases and prostaglandin synthetase as a function of time. The time dependent increase in stress ulcer correlates well with the concomitant increase in superoxide dismutase activity and decrease in peroxidase and prostaglandin synthetase activity. This creates a favourable condition for accumulation of endogenous H₂O₂ and more reactive hydroxyl radical (OH·). Administration of antioxidants such as reduced glutathione or sodium benzoate prior to stress causes significant decrease in ulcer index and lipid peroxidation and protection of gastric peroxidase activity suggesting the involvement of reactive oxygen species in stress induced gastric ulceration. This is supported by thein vitro observation that OH· can also inactivate peroxidase and induce lipid peroxidation. As prostaglandin is known to offer cytoprotection, stress-induced loss of prostaglandin synthetase activity appears to aggravate the oxidative damage caused by reactive oxygen species.Abbreviations ROS reactive oxygen species - GPO gastric peroxidase - SOD superoxide dismutase - MDA malondialdehyde - GSH reduced glutathione - TCA trichloroacetic acid     

Role of oxidative stress and antioxidant enzymes in Crohn's disease

There is increasing interest in oxidative stress being a potential aetiological factor and/or a triggering factor in Crohn's disease, rather than a concomitant occurrence during the pathogenesis of the disease. Recent research has shown that the immune mononuclear cells of Crohn's disease patients are induced to produce hydrogen peroxide (H2O2). Similarly, the regulation of antioxidant enzymes during disease in these cells has been unravelled, showing that SOD (superoxide dismutase) activity and GPx (glutathione peroxidase) activity is increased during active disease and returns to normal in remission phases. However, catalase remains constantly inhibited which supports the idea that catalase is not a redox-sensitive enzyme, but a regulator of cellular processes. ROS (reactive oxygen species) can be produced under the stimulus of different cytokines such as TNFα (tumour necrosis factor α). It has been shown in different experimental models that they are also able to regulate apoptosis and other cellular processes. The status of oxidative stress elements in Crohn's disease and their possible implications in regulating cellular processes are reviewed in the present paper.     

Effect of chilling on antioxidant enzymes and DPPH-radical scavenging activity of high- and low-vigour cucumber seedling radicles

The chilling tolerance of cucumber seedling radicles was influenced by their relative levels of vigour. Radicles of high‐vigour seedlings grew to 20 mm in length in 36 h at 25 °C, whereas it took 60 h for low‐vigour seedling radicles to reach that length. Chilling at 2·5 °C for 48 h inhibited the subsequent growth of high‐ and low‐vigour seedlings by 39 and 68%, respectively. The 2,3,5‐triphenyltetrazolium chloride (TTC) viability index, and α,α‐diphenyl‐β‐picrylhydrazyl (DPPH)‐radical scavenging activity were higher in high than low‐vigour radicles. Higher ascorbate peroxidase (APX) and catalase (CAT) enzyme activity, DPPH‐radical scavenging activity, and recovery of CAT activity after chilling in high‐vigour radicles corresponded with their higher level of chilling tolerance in comparison with low‐vigour radicles. In contrast, elevated levels of superoxide dismutase, glutathione reductase and guaiacol peroxidase appear to be correlated with chilling injury since they only showed substantial increases in activity in the more chilling‐­sensitive low‐vigour radicles after chilling. Manipulation of APX, CAT, and/or DPPH activity could produce plants with superior and persistent chilling tolerance.