根际低氧逆境对网纹甜瓜幼苗生长及根系呼吸代谢途径的影响

 以耐低氧性具有明显差异的两个网纹甜瓜(Cucumis melo var. raticulalus)品种为试材,研究了根际低氧胁迫下幼苗生长、根系活力及根系呼吸关键酶活性的变化。结果表明,根际低氧胁迫下,两品种幼苗生长均受到明显抑制,而根系活力升高;根系PDC活性两品种均显著提高,品种间无显著差异; MDH活性两品种均显著降低,且耐低氧性弱的‘西域一号’下降幅度较大;根系ADH和LDH活 性两品种均显著提高,耐低氧性强的‘东方星光’ADH活性增加的幅度显著高于耐低氧性弱的 ‘西域一号’,而‘西域一号’LDH活性增加幅度显著高于‘东方星光’。说明‘东方星光 ’在低氧胁迫下能保持较高的有氧呼吸水平,无氧呼吸的主要途径为乙醇发酵,而‘西域一 号’在低氧胁迫下无氧呼吸的主要途径为乳酸发酵。     

24-表油菜素内酯对低氧胁迫下黄瓜根系抗氧化系统及无氧呼吸酶活性的影响

用营养液水培,研究了根际低氧胁迫下24-表油菜素内酯(EBR)对2个抗低氧能力不同的黄瓜品种根系中抗氧化系统及无氧呼吸酶活性的影响。结果表明,在低氧胁迫下,EBR处理显著提高了低氧胁迫下2品种黄瓜幼苗根系SOD、POD及ADH活性,降低了O2-·、H2O2和MDA含量、LDH活性及‘中农八号’根系PDC活性,而对‘绿霸春四号’根系PDC及2个品种CAT活性无明显影响,表明外源EBR处理通过促进低氧胁迫下根系中抗氧化酶和ADH活性的提高,降低LDH活性及ROS含量,增强植株抗低氧胁迫的能力。     

土壤紧实胁迫对黄瓜根系呼吸代谢的影响

用容重分别为1.20和1.55 g·cm^-3的土壤进行盆栽试验,研究了土壤紧实胁迫对‘津春4号’黄瓜根系呼吸代谢的影响.结果表明: 土壤紧实胁迫条件下,黄瓜根系中丙酮酸脱羧酶、乙醇脱氢酶和乳酸脱氢酶活性显著提高;无氧呼吸主要产物(乙醇、乙醛和乳酸)含量显著升高;参与有氧呼吸的苹果酸脱氢酶、琥珀酸脱氢酶和异柠檬酸脱氢酶活性显著下降,丙酮酸和琥珀酸含量显著提高,苹果酸含量显著下降.说明在土壤紧实胁迫条件下,黄瓜根系的有氧呼吸受到显著抑制,无氧呼吸过程加强.     

土壤紧实胁迫对黄瓜根系呼吸代谢的影响

用容重分别为1.20和1.55 g· cm-3的土壤进行盆栽试验,研究了土壤紧实胁迫对‘津春4号'黄瓜根系呼吸代谢的影响.结果表明:土壤紧实胁迫条件下,黄瓜根系中丙酮酸脱羧酶、乙醇脱氢酶和乳酸脱氢酶活性显著提高;无氧呼吸主要产物(乙醇、乙醛和乳酸)含量显著升高;参与有氧呼吸的苹果酸脱氢酶、琥珀酸脱氢酶和异柠檬酸脱氢酶活性显著下降,丙酮酸和琥珀酸含量显著提高,苹果酸含量显著下降.说明在土壤紧实胁迫条件下,黄瓜根系的有氧呼吸受到显著抑制,无氧呼吸过程加强.     

外源亚精胺对低氧胁迫下黄瓜根系多胺含量和呼吸代谢酶活性的影响

采用营养液水培,研究了根际低氧胁迫下外源亚精胺对2个抗低氧能力不同的黄瓜品种(‘中农八号’和‘绿霸春四号’)根系中多胺含量和呼吸代谢相关酶活性的影响.结果表明,单纯低氧处理下,黄瓜幼苗根系中腐胺、亚精胺和精胺含量显著提高,异柠檬酸脱氢酶(IDH)和琥珀酸脱氢酶(SDH)活性显著降低,乳酸脱氢酶(LDH)、乙醇脱氢酶(ADH)和丙酮酸脱羧酶(PDC)活性显著提高.同时,与抗低氧能力弱的‘中农八号’相比,抗低氧能力强的‘绿霸春四号’根系LDH活性增加幅度较低,ADH活性增加幅度较高,IDH和SDH活性降幅也较小;外源亚精胺能显著提高低氧胁迫下黄瓜幼苗根系中亚精胺和精胺含量,降低腐胺含量;根系中LDH、ADH和PDC活性降低,IDH和SDH活性升高,说明黄瓜幼苗根系中较高的亚精胺、精胺含量可能有利于提高根系有氧呼吸能力,缓解低氧胁迫对植株的伤害.     

低氧胁迫对黄瓜幼苗根系无氧呼吸酶和抗氧化酶活性的影响

对两个抗低氧胁迫能力不同的黄瓜品种进行营养液水培,研究了低氧胁迫下植株根系中无氧呼吸酶和抗氧化酶活性的变化。结果表明,低氧胁迫下,黄瓜植株生长受到抑制,鲜重和干重显著降低,根系中蛋白质含量降低,而根系中乳酸脱氢酶（LDH）、丙酮酸脱羧酶（PDC）、乙醇脱氢酶（ADH）、超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性在低氧胁迫下显著提高,且提高的幅度与品种抗低氧胁迫能力的强弱有关,与“中农8号”相比,抗低氧性胁迫能力较强的“绿霸春四号”根系内LDH活性增幅较小,而ADH、PDC、SOD、POD和CAT活性增幅较大。说明较高的ADH、PDC、SOD、POD、CAT活性和较低的LDH活性有利于增强幼苗植株抗低氧胁迫的能力。     

渗透胁迫下小麦根系渗透调节与根冠淀粉水解的研究

用不同浓度的PEG—600对抗旱性不同的小麦幼苗进行渗透胁迫处理,研究了小麦幼苗根系的淀粉酶活性、可溶性糖含量、渗透势、渗透调节能力和根冠淀粉的水解状况。结果表明,随着渗透胁迫程度的加重,抗旱性强的小麦品种昌乐5号和北农2号根系渗透势和饱和渗透势的降低程度大于抗旱性弱的小麦品种鲁麦5号和921842,并且抗旱性强的小麦品种根系的渗透调节能力大于抗旱性弱的小麦品种。随着渗透胁迫程度的加重．各品种小麦根冠淀粉粒均有不同程度的减少。而抗旱性强的品种根冠淀粉粒的减少程度小于抗旱性弱的品种;抗旱性强的小麦品种根系淀粉酶活性显著高于抗旱性弱的小麦品种,但是,随着渗透胁迫程度的加重,抗旱性弱的品种淀粉酶活性增加的幅度远高于抗旱性强的品种。可溶性糖含量的变化趋势与淀粉酶活性的变化趋势一致．即渗透胁迫下根冠淀粉水解程度大的小麦品种,可溶性糖的含量高。但根冠淀粉水解在根系的渗透调节以及在小麦适应水分胁迫中的作用还有待于进一步探讨。     

茄子嫁接苗根系对低温环境胁迫的响应

以‘济农2000’为对照,研究了低温胁迫下不同抗冷性茄子砧木嫁接苗根系的生理生化变化及其与抗冷性的关系.结果表明,在10 ℃(昼)/3 ℃(夜)低温处理初期,根系对低温最敏感,表现为MDA含量、冷害指数、POD活性、脯氨酸含量、可溶性蛋白含量等迅速增加,而根系呼吸速率、SOD、CAT活性等迅速降低.随着低温胁迫时间的延长,根系呼吸速率持续降低,而冷害指数持续升高,渗透调节物质基本呈增加的趋势.常温恢复3 d后,呼吸速率、渗透调节物质、SOD活性等升高,但均以抗冷性较强的赤茄砧木嫁接苗恢复能力较强,而抗冷性较弱的台茄砧木嫁接苗与自根苗较差.利用抗冷性较强的砧木进行嫁接,可显著增强茄子根系的活性,进而提高其抗冷性.     

D-精氨酸对低氧胁迫下黄瓜幼苗根系多胺含量和无氧呼吸代谢的影响

采用营养液水培法,研究了根际低氧胁迫下D-精氨酸（D-Arg）对两个抗低氧能力不同的黄瓜品种根系中多胺含量和无氧呼吸代谢的影响.结果表明,低氧处理下,黄瓜幼苗根系中多胺含量显著增加,无氧呼吸代谢能力提高;与抗低氧能力弱的‘中农八号’相比,抗低氧能力强的‘绿霸春四号’根系中乙醇发酵活性较高,乳酸发酵活性较低;低氧胁迫下,D-精氨酸能显著降低黄瓜幼苗根系中腐胺、亚精胺和精胺含量,根系中乙醇脱氢酶（ADH）和乳酸脱氢酶（LDH）活性增加,乙醇和乳酸含量升高,植株生长受到抑制,而外源腐胺能缓解D-精氨酸的这种作用.说明黄瓜幼苗根系中较高的多胺含量可能有利于缓解低氧胁迫对植株造成的伤害.     

Ca2+对低氧胁迫下黄瓜幼苗生长和根系无氧呼吸酶的影响

采用营养液水培,以抗低氧能力不同的2个黄瓜品种为试材,研究了Ca2+对黄瓜幼苗植株生长和根系无氧呼吸酶活性的影响.结果表明,在低氧胁迫下,LDH、PDC和ADH活性提高程度与幼苗的抗低氧性和Ca2+浓度密切相关.与抗低氧性较弱的"中农8号"相比,抗低氧性强的"绿霸春4号"幼苗根系LDH活性增加缓慢,而PDC和ADH活性增加幅度较大,因此增强了植株对低氧胁迫的抗性.低氧胁迫下,营养液中8 mmol·L-1 Ca2+处理能显著提高根系ADH活性,降低LDH和PDC活性,0 mmol·L-1 Ca2+处理表现出相反的规律.由此可以说明,低氧胁迫下,Ca2+能够提高ADH活性,降低LDH和PDC活性,可增强黄瓜植株对低氧胁迫的抗性.     

水分胁迫下小麦幼苗呼吸代谢的改变

水分胁迫下小麦幼苗叶和根的呼吸速率变化模式不同:叶片呼吸在胁迫初期升高,然后随相对含水量进一步递减而急剧下降;根的呼吸速率随相对含水量降低成指数下降。自然干旱和PEG渗透胁迫下得到的结果基本一致。小麦叶片在轻度水分胁迫下呼吸上升与磷酸化解偶联有关。水分胁迫也引起呼吸代谢途径的改变。轻度水分胁迫使叶片呼吸速率升高时,EMP途径运行程度稍有上升;增加的呼吸主要通过TCAC;线粒体呼吸中通过细胞色素主链的电子流量增加,抗氰交替途径的相对运行程度下降。当水分胁迫降低根呼吸速率时,EMP和TCAC的运行程度明显降低;细胞色素途径的运行程度也下降,但仍传递大约一半的呼吸电子流。     

小麦幼苗叶片抗氰呼吸对轻度水分胁迫的响应

小麦幼苗经－０．５ＭＰa聚乙二醇（ＰＥＧ－６０００）溶液暗中渗透迫０、６、１２、１８、２４、３０、３６、４２、４８h,叶片的总呼吸速率（Ｖt)呈现先上升后降低的趋势,交替途径呼吸也表现出相同的变化模式。水分胁迫初期（０－１２h),交替途径容量（Ｖalt)、实际运行活性（ρValt)及运行系数（ρ值）均上升,此后（１８－４８h）逐渐下降,水分胁迫也影响了呼吸电子流在２条呼吸途径中的分配比例,胁迫初期的０－１２h内,流经交替途径的电子流增多,而流向细胞色素主路的电子流减少,但随着胁迫时间的延长,交替途径的贡献降低,而细胞色素主路的贡献增加,说明小麦叶片的抗氰呼吸在水分胁迫初期被诱导增加,而随着胁迫进行的延长又表现为下降。     

轻度水分胁迫的小麦幼苗中与呼吸有关的几种酶活性变化

轻度水分胁迫使小麦幼苗叶片呼吸升高时,叶中琥珀酸去氢酶和细胞色素氧化酶活性均明显升高;而同样胁迫使根呼吸下降时,根中这两种酶活性均明显下降。叶和根中ATP酶分解活性在胁迫下都明显升高。轻度水分胁迫使叶片过氧化氢酶活性升高。叶中有明显的乙醇酸氧化酶活性,抗旱品种的酶活性较高,胁迫使此酶活性降低。     

Effect of Osmotic Stress in Early Stages of Ontogenesis on Root Respiration, Growth, Sugar Content, and Cell Injury in Maize Seedlings Differing in Drought Sensitivity

Cultivars of maize （Zea mays L.） with different sensitivity to drought were exposed to 0.3 mol/L sorbitol （-1.4 MPa water potential） for 24 h. Exposure to water deficiency significantly reduced the growth of both shoots （coleoptile and hypocotyl） and roots. Shoot growth was inhibited more than the growth of roots. Osmotic stress enhanced accumulation of soluble sugars. Electrolyte leakage, a cell injury index, was slightly increased after 0.3 mol/L sorbitoh Respiration was measured in the presence and absence of 2,6-dlchloro-phenol indophenoh 2,6-Dichloro-phenol indophenol did not influence respiration rates, because statistically equal results were observed under both conditions. Total respiration （VT） decreased after osmoticum treatment. There were no significant differences in the VT among the cultlvars analysed. The decrease In VT was caused by a decline In the activities and capacities of both cytochrome （Vcyt, Vcyt） and alternative pathway （Valt, Valt） of respiration. A high residual respiration （Vres） was observed, up to 27% of total uninhibited respiration. The result of uncoupler use clearly indicated that coupling was maintained after 24 h of osmotic stress. The recovery of the respiration rate was comparable with that of non-stressed control rates. According to these observations, no possible mltochondrial damage is expected. Water deficiency did not induce a stimulation of the alternative oxidase, so we assume that the stimulation of the alternative pathway is not related to drought stress resistance; rather, the function of the alternative pathway is to balance carbon metabolism and electron transport in a response to a changing environment.     

渗透胁迫和CO~(++)对小麦幼苗内源多胺含量和乙烯产生的影响

抗旱和不抗旱的小麦幼苗叶片与根系,在1MPaPEG渗透胁迫下释出乙烯和生成内源腐胺、亚精胺和精胺的数量增加。当增加2mmol钴离子处理6h和12h后,乙烯生成显著受到抑制,而亚精肢和精胺呈现进一步增加。表明钴离子阻遏了氨基环烷羧酸向乙烯转变的途径,并为多胺合成提供了更多的底物,从而有利于提高小麦抗衰老和抗旱的能力,抗旱品种表现更为明显。     

Modulation of osmotic stress effects on photosynthesis and respiration by temperature in mesophyll protoplast of pea

Exposure of mesophyll protoplast of pea to osmotic stress decreases the rate of photosynthesis while stimulating marginally the respiratory rate of mesophyll protoplasts. The interaction of osmotic and temperature stress during the modulation of photosynthetic and respiratory rates of pea (Pisum sativum var Azad P1) mesophyll protoplasts was investigated. The protoplasts were exposed to either iso-osmotic (0.4 M) or hyper-osmotic (1.0 M) concentration of sorbitol at 15 degrees and 25 degrees C. The rates of photosynthesis and respiration were studied. At optimum temperature of 25 degrees C, there was a decrease in photosynthesis (< 10%) at hyper-osmoticum (osmotic effect), whereas respiration increased marginally (by about 15%). Low temperature (15 degrees C) aggravated the sensitivity of both respiration and photosynthesis to osmotic stress. At 15 degrees C, the decrease in photosynthesis due to osmotic stress was > 35%, while the respiratory rate was stimulated by 30%. The relative proportion of cytochrome pathway decreased by about 50% at both 15 degrees C and 25 degrees C while that of alternative pathway increased, more so, at 15 degrees C, when the mesophyll protoplasts were subjected to hyper-osmoticum stress. The titration experiments showed that extent of engagement of alternative pathway was higher, the slope value was slightly higher for 15 degrees C compared to 25 degrees C. Low temperature modulates the effect of hyper-osmoticum stress on photosynthesis and respiration, and results in increased participation of alternative pathway.     

Respiratory pathways in germinating maize radicles correlated with desiccation tolerance and soluble sugars

We have assessed the activities of the cytochrome and alternative pathways in total respiration and their role in each stage of germination of Zea mays L. radicles. Throughout imbibition, the salicylhydroxamic acid (SHAM) concentration needed to inhibit the cyanide-resistant pathway, without any side effects, decreased from 15 m M in quiescent embryos to 5 m M at 72 h after imbibition. Electrons predominantly flowed through the cytochrome pathway although the alternative pathway was already present at early imbibition. The capacity of the alternative path was about 70% of the control rate of respiration. Its engagement progressively increased from 18% after 10 min of imbibition to 70% at the radicle emergence and then decreased to 50% at 96 h after imbibition, concomitant with the onset of radicle growth. The alternative pathway was, however, not essential for germination. The observed activity of the alternative path correlated with the monosaccharide (glucose + fructose) content, suggesting that the alternative pathway could be acting according to the 'energy overflow model'. On the other hand, up to 24 h after imbibition at 16°C, maize radicles tolerate a severe desiccation, becoming intolerant at 72 h. On reimbibition of tolerant radicles, respiration increased immediately and the alternative pathway was rapidly engaged. At 72 h, no respiration was measured, indicating a total loss of the respiratory systems. The possible correlation between carbohydrate content, loss of desiccation tolerance and activity of the two respiratory pathways is discussed.     

Exogenous Nitric Oxide (as Sodium Nitroprusside) Ameliorates Polyethylene Glycol-Induced Osmotic Stress in Hydroponically Grown Maize Roots

The present study was designed to examine whether exogenous sodium nitroprusside (SNP) supplementation has any ameliorating action against PEG-induced osmotic stress in Zea mays cv. FRB-73 roots. Twenty percent or 40 % polyethylene glycol (PEG6000; ?0.5 MPa and ?1.76 MPa, respectively) treatment alone or in combination with 150 and 300 μM SNP was applied to hydroponically grown maize roots for 72 h. Although only catalase (CAT) activity increased when maize roots were exposed to PEG-induced osmotic stress, induction of this antioxidant enzyme was inadequate to detoxify the extreme levels of reactive oxygen species, as evidenced by growth, water content, superoxide anion radical (O ₂ ^?? ), hydroxyl radical (OH^?) scavenging activity, and TBARS content. However, supplementation of PEG-exposed specimens with SNP significantly alleviated stress-induced damage through effective water management and enhancement of antioxidant defense markers including the enzymatic/non-enzymatic systems. Exogenously applied SNP under stress resulted in the up-regulation of glutathione peroxidase (GPX), glutathione S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), total ascorbate, and glutathione contents involved in ascorbate–glutathione cycle. On the other hand, growth rate, osmotic potential, CAT, APX, GR, and GPX increased in maize roots exposed to both concentrations of SNP alone, but activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase decreased. Based on the above results, an exogenous supply of both 150 and 300 μM SNP to maize roots was protective for PEG-induced toxicity. The present study provides new insights into the mechanisms of SNP (NO donor) amelioration of PEG-induced osmotic stress damages in hydroponically grown maize roots.     

渗透胁迫对水稻幼苗膜脂过氧化及体内保护系统的影响

两个不同抗旱性的水稻品种对PEG6000渗透胁迫(-0.5MPa,-0.8MPa)的反应具有一定差异。渗透胁迫下SOD,POD和CAT活性及Vc,Car含量与膜脂过氧化水平及膜透性呈一定负相关性,表明这些指标可作为水稻抗旱育种的参考依据。     

Polyribosome metabolism, growth and water status in the growing tissues of osmotically stressed plant seedlings

Relationships between growth of osmotically stressed intact seedlings and polyribosome levels and water status of growing tissues were examined. Sudden exposure of barley (Hordeum vulgare L. cv. Arivat) roots to a solution of ?0.8 MPa polyethylene glycol caused leaf growth to stop almost immedately, but growth resumed at a much lower rate after 0.5–1 h. In the growing region of leaves, the polyribosome: total ribosome ratio of free (non-membrane-bound) ribosomes was significantly reduced after 15 min stress, but a decrease in the large polyribosome:total polyribosome ratio occurred only after 1–2 h. Membrane-bound and free polyribosome levels both decreased to 70% of unstressed control values after 4 h stress. Recovery of total polyribosomes occurred within 1 h after relief of 4 h stress, but required 3 h after relief of 24 h stress. Stress detectably reduced the water potential and osmotic potential of growing tissue within 0.5–1.0 h, and osmotic adjustment continued for up to 10 h. Recovery of water status was incomplete after 1 h relief of a 4 h stress. In contrast, expanded blade tissues of stressed plants underwent minor changes in water status and slow decreases in polyribosomes levels. These results confirm that growing tissues of barley leaves are selectively responsive to stress, and suggest that changes in growth, water status and polyribosome levels may be initiated by the same signal. Measurements of seedling growth, polyribosome levels and water status of growing tissues of barley and wheat (Triticum aestivum L. cv. Zaragoza) leaves, etiolated pea (Pisum sativum L. cv. Alaska) epicotyl and etiolated squash (Cucurbita pepo L. cv. Elite) hypocotyl stressed with polyethylene glycol solutions of ?0.3 to ?0.8 MPa for 12 h or more showed that polyribosome levels were highly correlated with seedling growth rate as well as with tissue water and osmotic potentials, while turgor remained unchanged. These results suggest that long-term growth of osmotically stressed plants may be limited by a reduced capacity for protein synthesis in growing tissues and is not dictated by turgor loss.