Nitric oxide counteracts the senescence of rice leaves induced by abscisic acid

In the present study, we evaluate the protective effect of nitric oxide (NO) against senescence of rice leaves promoted by ABA. Senescence of rice leaves was determined by the decrease of protein content. ABA treatment resulted in (1) induction of leaf senescence, (2) increase in H2O2 and malondialdehyde (MDA) contents, (3) decrease in reduced form glutathione (GSH) and ascorbic acid (AsA) contents, and (4) increase in antioxidative enzyme activities (superoxide dismutase, ascorbate peroxidase, glutathione reductase, and catalase). All these ABA effects were reduced by free radical scavengers such as sodium benzoate and GSH. NO donors [N-tert-butyl-alpha-phenylnitrone (PBN), sodium nitroprusside, 3-morpholinosydonimine, and AsA + NaNO2] were effective in reducing ABA-induced leaf senescence. PBN prevented ABA-induced increase in the contents of H2O2 and MDA, decrease in the contents of GSH and AsA, and increase in the activities of antioxidative enzymes. The protective effect of PBN on ABA-promoted senescence, ABA-increased H2O2 content and lipid peroxidation, ABA-decreased GSH and AsA, and ABA-increased antioxidative enzyme activities was reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a NO-specific scavenger, suggesting that the protective effect of PBN is attributable to NO released. Reduction of ABA-induced senescence by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H2O2.     

Inhibition of methyl jasmonate-promoted senescence in rice leaves by a metal chelator, 2,2′-bipyridine

The possible mediatory role of transition metals in methyl jasmonate- (MJ-)induced senescence of rice leaves was investigated. Metal chelators(2,2-bipyridine, 8-hydroxylquinoline and 1,10-phenanthroline) reducedMJ-promoted senescence of rice leaves. The reduction of MJ-promoted senescenceby 2,2-bipyridine(BP) is closely associated with the decrease in lipidperoxidation and increase in activity of superoxide dismutase (SOD). Our resultssuggest that iron or copper plays a major role in MJ-promoted senescence ofdetached rice leaves. BP-reduced senescence of detached rice leaves induced byMJ was reversed by adding Fe²⁺ or Cu²⁺, but notby Mn²⁺ or Mg²⁺. Reduction of MJ-promotedsenescence of detached rice leaves by BP is most likely mediated throughchelation of iron or copper and an increase in SOD activity.     

Nitric oxide acts as an antioxidant and delays methyl jasmonate-induced senescence of rice leaves

In the present study, we evaluate the protective effect of nitric oxide (NO) against senescence of rice leaves promoted by methyl jasmonate (MJ). Senescence of rice leaves was determined by the decrease of protein content. MJ treatment resulted in (1) induction of leaf senescence, (2) increase in H₂O₂ and malondialdehyde (MDA) contents, (3) decrease in reduced form glutathione (GSH) and ascorbic acid (AsA) contents, and (4) increase in antioxidative enzyme activities (ascorbate peroxidase, glutathione reductase, peroxidase and catalase). All these MJ effects were reduced by free radical scavengers such as sodium benzoate and GSH. NO donors [N-tert-butyl-α-phenylnitrone (PBN), sodium nitroprusside, 3-morpholinosydonimine, and AsA+NaNO₂] were effective in reducing MJ-induced leaf senescence. PBN prevented MJ-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of GSH and AsA, and increase in the activities of antioxidative enzymes. The protective effect of PBN on MJ-promoted senescence, MJ-increased H₂O₂ content and lipid peroxidation, MJ-decreased GSH and AsA, and MJ-increased antioxidative enzyme activities was reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, a NO-specific scavenger, suggesting that the protective effect of PBN is attributable to NO released. Reduction of MJ-induced senescence by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H₂O₂     

Differential effect of sorbitol and polyethylene glycol on antioxidant enzymes in rice leaves

Polyethylene glycol (PEG) and sorbitol (ST) have each been used inosmotically induced water stress studies in plants, however, these osmotica maynot have equivalent effects in plants. The present study was designed to examinewhether antioxidant enzyme responses in rice leaves are different for PEG and STof osmotic potential –1.5 MPa. As judged by relative watercontent, PEG treatment resulted in a higher degree of water stress in riceleaves than ST treatment. PEG treatment markedly increased lipid peroxidation,judged by malondialdehyde content, in rice leaves. However, ST treatment had noeffect on lipid peroxidation. An increase in peroxidase (POX), ascorbateperoxidase (APX) and glutathione reductase (GR) activities was observed in riceleaves treated with ST. PEG treatment had no effect on POX and APX activitiesand decreased GR activity in rice leaves. The decrease in superoxide dismutaseactivity induced by PEG was more pronounced than by ST. Cycloheximide blockedthe enhanced activities of POX, APX and GR by ST, indicating de novo synthesisof the enzymes. Results suggest that ST but not PEG treatment can up-regulateantioxidant system in rice leaves.     

杂交稻及其三系叶片衰老过程中SOD、CAT活性和MDA含量的变化

对杂交水稻及其三系主茎第11叶叶片自然衰老过程中超氧物歧化酶(SOD)、过氧化氢酶(CAT)和丙二醛(MDA)含量的变化进行了研究,结果表明:叶片衰老过程中,SOD和CAT活性下降,MDA的含量增加,可作为衰老特征的叶绿素和可溶性蛋白质含量明显下降;SOD的活性和MDA的含量变化相对应;CAT活性大幅度下降与SOD之间的不平衡,致使O_2~-代谢中间产物累积而引起膜的损伤。不育系的衰老进程比杂交水稻、恢复系和保持系慢,其SOD和CAT活性明显高于其它三者,可能是不育系不易早衰的原因之一。     

Cadmium toxicity is reduced by nitric oxide in rice leaves

We evaluate the protective effect of nitric oxide (NO) against Cadmium (Cd) toxicity in rice leaves. Cd toxicity of rice leaves was determined by the decrease of chlorophyll and protein contents. CdCl₂ treatment resulted in (1) increase in Cd content, (2) induction of Cd toxicity, (3) increase in H₂O₂ and malondialdehyde (MDA) contents, (4) decrease in reduced form glutathione (GSH) and ascorbic acid (ASC) contents, and (5) increase in the specific activities of antioxidant enzymes (superoxide dismutase, glutathione reductase, ascorbate peroxidase, catalase, and peroxidase). NO donors [N-tert-butyl-α-phenylnitrone, 3-morpholinosydonimine, sodium nitroprusside (SNP), and ASC + NaNO₂] were effective in reducing CdCl₂-induced toxicity and CdCl₂-increased MDA content. SNP prevented CdCl₂-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of GSH and ASC, and increase in the specific activities of antioxidant enzymes. SNP also prevented CdCl₂-induced accumulation of NH₄ ⁺, decrease in the activity of glutamine synthetase (GS), and increase in the specific activity of phenylalanine ammonia-lyase (PAL). The protective effect of SNP on CdCl₂-induced toxicity, CdCl₂-increased H₂O₂, NH₄ ⁺, and MDA contents, CdCl₂-decreased GSH and ASC, CdCl₂-increased specific activities of antioxidant enzymes and PAL, and CdCl₂-decreased activity of GS were reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, a NO scavenger, suggesting that protective effect by SNP is attributable to NO released. Reduction of CdCl₂-induced toxicity by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H₂O₂.     

The Effect of Polyethylene Glycol on Proline Accumulation in Rice Leaves

The regulation of proline accumulation in polyethylene glycol (PEG, –1.5 MPa) treated rice leaves was investigated. PEG treatment resulted in a decrease in relative water content, indicating that PEG treatment caused water stress in rice leaves. Proline accumulation caused by PEG was related to protein hydrolysis, an increase in ornithine--amino- transferase activity, an increase in the content of ammonia, and an increase in the contents of the precursors of proline biosynthesis, glutamic acid, ornithine, and arginine. Results also show that abscisic acid accumulation is not required for proline accumulation in PEG-treated rice leaves.     

水稻叶片的衰老与超氧物歧化酶活性及脂质过氧化作用的关系

研究了从抽穗开花到籽粒成熟过程中,水稻植株顶部三片叶子的超氧物歧化酶(SOD),脂质过氧化产物丙二醛(MDA)含量及二磷酸核酮糖羧化酶活性的变化。实验结果表明:叶片的衰老伴随着 SOD 活性、RuBP 羧化酶活性及叶绿素含量的降低、丙二醛含量显著增高。分离了三个 SOD 的同工酶,证明为 Cu—Zn SOD。观察了 SOD 同工酶在叶片老化及酶液存放不同时间中的变化。讨论了叶片衰老过程中氧自由基对酶及质膜的损伤影响。     

Superoxide Dismutase Activity and Lipid Peroxidation in Relation to Senescence of Rica Leaves

Superoxide dismutase (SOD), lipid peroxidation, ribulose 1, 5-bisphosphate earboxylasc and chlorophyll content in the leaves of rice were investigated during bloomJug to ripening stages. The results indicated that leaf senescence was associated with the decreascs of SOD and RuBP earboxylase activities and chlorophyll content. A marked increase of malondialdehyde(MDA)contcnt, a produet of lipid pcroxidation was observed during leaf senescence, However, the relative high activities of SOD and RuBP earboxylase and chlorophyll content, lower MDA content in hybrid rice senescenee leaves, compared with their three lines, suggest the presence of physiological hybrid vigor. The analysis of polyacrylamide gel eleetrophoresis showed that three SOD isozymes in leaf extract, which were Cu-Zn SOD. Changes of SOD isozymes were observed during leaf agling and at different time of storage of its extract. The destroying effect of oxygen free radical on enzymes and membrane in the course of leaf senescence was discussed.     

Nitric oxide alleviates arsenic toxicity by reducing oxidative damage in the roots of Oryza sativa (rice)

Nitric oxide (NO) is a bioactive gaseous, multifunctional molecule playing a central role and mediating a variety of physiological processes and responses to biotic and abiotic stresses including heavy metals. The present study investigated whether NO applied exogenously as sodium nitroprusside (SNP) has any protective role against arsenic (As) toxicity in Oryza sativa (rice). Treatment with 50 μM SNP (a NO donor) significantly ameliorated the As-induced (25 or 50 μM) decrease in root and coleoptile length of rice. Further, As-induced oxidative stress measured in terms of malondialdehyde (MDA), superoxide ion (), root oxidizability and H₂O₂ content was lesser upon supplementation of NO. It indicated a reactive oxygen species (ROS) scavenging activity of NO. NO addition reversed (only partially) the As-induced increase in activities of antioxidant enzymes – superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, and catalase. The study concludes that exogenous NO provides resistance to rice against As-toxicity and has an ameliorating effect against As-induced stress.     

棉花叶片衰老过程中激素和膜脂过氧化的关系

以陆地棉品种辽棉9号的去根幼苗为材料,对其进行暗诱导衰老培养.在培养液中分别加入6-BA、ABA、GSH、H2O2、CaCl2、A23187 和A23187 CaCl2,测定在不同培养条件下棉花去根幼苗叶片内源激素、SOD酶活性和MDA含量的变化.结果表明:棉花叶片衰老表现为细胞分裂素含量的下降和ABA含量的上升.6-BA、GSH和钙离子均延缓叶片的衰老,ABA和H2O2促进叶片的衰老.     

Paclobutrazol delayed dark-induced senescence of mung bean leaves

Sixty days old mung beans Vigna radiata (L.) Wilczek were treated with soil applied paclobutrazol, at the rate of 500 μg per 10 inch pot. After seven days of application, the plants along with untreated controls were transferred to the dark for induction of senescence. The treated plants exhibited higher chlorophyll content and activity of catalase (CAT) compared to controls. In contrast, control leaves had higher activity of peroxidase (POX) and a higher content of malondialdehyde (MDA), while superoxide dismutase (SOD) activity remained unchanged. Upon transfer to dark, chlorophyll content declined in both control and treated plants but the decline was much faster in control. The activity of CAT decreased significantly in controls while POX activity and MDA content remained higher in control than in treated plants. Paclobutrazol delayed the dark-induced senescence in attached mung bean leaves in association with the maintenance of higher activity of CAT, low activity of POX, and low MDA contents. The variation in SOD activity was not discernible with senescence levels.     

萝卜离体子叶衰老与膜脂过氧化的关系

萝卜离体子叶在光下或暗中衰老及激素调节衰老过程中,作为叶片衰老指标的叶绿素和蛋白质含量的降低,发生在MDA含量增高之前,更早于SOD活性的下降。表明由SOD活性降低所导致的膜脂过氧化的增强,并非衰老的原初反应,而是叶片衰老到一定程度的生理变化。因此,至少在萝卜离体子叶上,不能将其衰老的启动归因于受SOD控制的膜脂过氧化作用导致的膜累积性质变。     

褐飞虱侵害对水稻叶片、根SOD活性及丙二醛含量的影响

以分蘖期水稻协优963、TN1为供试材料,研究褐飞虱Nilaparvata lugens(St(a)l)侵害后水稻叶片、根超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量变化情况.结果表明:协优963、TN1叶片SOD活性变化不明显;15和30头/株侵害协优963后3、6、9d根SOD活性分别显著下降了88.4%和7...     

Cadmium toxicity of rice leaves is mediated through lipid peroxidation

Oxidative stress, in relation to toxicity of detached rice leaves,caused by excess cadmium was investigated. Cd content inCdCl₂-treated detached rice leaves increased with increasingdurationof incubation in the light. Cd toxicity was followed by measuring the decreasein chlorophyll and protein. CdCl₂ was effective in inducing toxicityand increasing lipid peroxidation of detached rice leaves under both light anddark conditions. These effects were also observed in rice leaves treated withCdSO₄, indicating that the toxicity was indeed attributed to cadmiumions. Superoxide dismutase (SOD), ascorbate peroxidase (APOD), and glutathionereductase (GR) activities were reduced by excess CdCl₂ in the light.The changes in catalase and peroxidase activities were observed inCdCl₂-treated rice leaves after the occurrence of toxicity in thelight. Free radical scavengers reduced CdCl₂-induced toxicity and atthe same time reduced CdCl₂-induced lipid peroxidation and restoredCdCl₂-decreased activities of SOD, APOD, and GR in the light. Metalchelators (2,2-bipyridine and 1,10-phenanthroline) reducedCdCl₂ toxicity in rice leaves in the light. The reduction ofCdCl₂ toxicity by 2,2-bipyridine (BP) is closely associatedwith a decrease in lipid peroxidation and an increase in activities ofantioxidative enzymes. Furthermore, BP-reduced toxicity of detached riceleaves,induced by CdCl₂, was reversed by adding Fe²⁺ orCu²⁺, but not by Mn²⁺ or Mg²⁺.Reduction of CdCl₂ toxicity by BP is most likely mediated throughchelation of iron. It seems that toxicity induced by CdCl₂ mayrequire the participation of iron.     

Silicon alleviates simulated acid rain stress of <Emphasis Type="BoldItalic">Oryza sativa</Emphasis> L. seedlings by adjusting physiology activity and mineral nutrients

Silicon (Si) has been a modulator in plants under abiotic stresses, such as acid rain. To understand how silicon made an effect on rice (Oryza sativa L.) exposed to simulated acid rain (SAR) stress, the growth, physiologic activity, and mineral nutrient content in leaves of rice were investigated. The results showed that combined treatments with Si (1.0, 2.0, or 4.0 mM) and SAR (pH 4.0, 3.0, or 2.0) obviously improved the rice growth compared with the single treatment with SAR. Incorporation of Si into SAR treatment decreased malondialdehyde (MDA) content; increased soluble protein and proline contents; promoted CAT, POD, SOD, and APX activity; and maintained the K, Ca, Mg, Fe, Zn, Cu content balance in leaves of rice seedlings under SAR stress. The moderate concentration of Si (2.0 mM) was better than the low and high concentration of Si (1.0 and 4.0 mM). Therefore, application of Si could be a better strategy for maintaining the crop productivity in acid rain regions.     

Changes in ammonium ion content and glutamine synthetase activity in rice leaves caused by excess cadmium are a consequence of oxidative damage

Ammonium ion accumulation and the decrease in glutamine synthetase (GS)activity induced by CdCl₂ were investigated in relation to lipidperoxidation in detached rice leaves. CdCl₂ was effective inincreasing ammonium ion content, decreasing GS activity and increasing lipidperoxidation. Free radical scavengers (glutathione, thiourea, sodium benzoate)and an iron chelator (2,2-bipyridine) were able to inhibit the decreasein GS activity and ammonium ion accumulation caused by CdCl₂ and atthe same time inhibit CdCl₂-induced lipid peroxidation. Paraquat,which is known to produce oxygen radicals, decreased GS activity, increasedammonium ion content, and increased lipid peroxidation. GS1 appears to be thepredominant isoform present. Excess Cd caused a decrease in GS1 but not in GS2in detached rice leaves. An increase in lipid peroxidation preceded ammoniumionaccumulation and the decrease in GS1 activity. These results suggest that thedecrease in GS activity and the accumulation of ammonium ions in detached riceleaves are a consequence of oxidative damage caused by excess Cd.     

The effect of NaCl on proline accumulation in rice leaves

The regulation of proline accumulation in detached leaves of rice(Oryza sativa cv. Taichung Native 1) was investigated.Increasing concentrations of NaCl from 50 to 200 mM progressivelyincreased proline content in detached rice leaves. NaCl induced prolineaccumulation was mainly due to the effect of both Na⁺ andCl^– ions. Proline accumulation caused by NaCl was related toprotein proteolysis, an increase in ornithine--aminotransferaseactivity,a decrease in proline dehydrogenase activity, a decrease in prolineutilisation,and an increase in the content of the precursors of proline biosynthesis,ornithine and arginine. Results also show that proline accumulation caused byNaCl was associated with ammonium ion accumulation.     

施氮量和花后土壤含水量对小麦旗叶衰老及粒重的影响

在防雨池栽培条件下,研究了施氮量和花后土壤含水量对小麦旗叶衰老和粒重的影响.结果表明：各氮肥处理下,小麦旗叶SPAD值、可溶性蛋白质含量、超氧化物歧化酶（SOD）活性、过氧化氢酶（CAT）活性和光合速率（P_n）均表现为：花后土壤含水量60%～70%处理>80%～90%处理>40%～50%处理,小麦旗叶丙二醛（MDA）含量表现为：花后土壤含水量40%～50%处理>80%～90%处理>60%～70%处理,表明花后土壤含水量过高或过低均可导致小麦旗叶早衰,影响籽粒灌浆,降低粒重.在花后相同土壤含水量条件下,旗叶SPAD值、可溶性蛋白质含量、SOD活性、CAT活性和P_n均随施氮量的增加而升高,MDA含量随施氮量的增加而降低,表明增施氮肥可以延缓小麦旗叶衰老,但过量施用氮肥则不利于小麦粒重的提高,尤其是在花后土壤缺水的情况下,施用过多氮肥可导致小麦粒重下降.在小麦生产中可以将施用氮肥和控制花后土壤水分含量相结合,延缓小麦植株衰老,提高粒重.     

海滨滨麦叶片和根对不同厚度沙埋的生理响应差异分析

以烟台海岸抗风沙植物滨麦为研究材料,通过对不同厚度沙埋下其叶片和根部抗氧化酶活力(超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT))、丙二醛(MDA)含量和渗透调节物含量变化的分析,探讨了叶片和根部对沙埋生理响应的差异。试验按滨麦成株株高(约40 cm)对其进行了轻度沙埋(在株高1/4处)、中度沙埋(2/4处)和重度沙埋(3/4处)。在沙埋第6天,分别测定了不同厚度沙埋处理下,植株各段叶片和根抗氧化酶活力、MDA和渗透调节物含量。结果表明,轻度和中度沙埋均加速植株生长。与对照相比,经轻度、中度沙埋处理6 d,叶片平均MDA含量增加,在重度沙埋下降低。不同厚度沙埋6 d,叶片平均SOD活力和脯氨酸含量增加,而CAT活力、可溶性糖和可溶性蛋白质含量下降。但不同厚度沙埋均使沙上叶片MDA、脯氨酸、可溶性蛋白质含量和SOD和CAT活力增加,尤其是叶片顶部增加最为明显,使沙下叶片MDA、可溶性糖、可溶性蛋白质含量和CAT活力下降,导致同株沙上和沙下叶片MDA、脯氨酸、可溶性糖、可溶性蛋白质含量和SOD和CAT活力差异显著(P0.05)。与叶片相比,根中MDA、可溶性蛋白质含量和SOD和CAT活力较低,而POD活力和可溶性糖含量较高并与叶片差异显著(P0.05)。不同厚度沙埋6 d,滨麦根中MDA和可溶性蛋白质含量变化较小,可溶性糖含量和CAT、POD、SOD活力略有降低。研究表明,滨麦根和叶片对不同厚度沙埋的生理响应不同。沙埋直接作用于叶片并诱发叶内氧自由基积累,但叶片通过快速激活的抗氧化酶保护系统(CAT、SOD)维持氧自由基代谢平衡,以及渗透调节物(脯氨酸、可溶性糖)的积累维护细胞水分代谢平衡,并满足能量的需求和快速生长。但在不同厚度沙埋下,由于根系不受沙埋直接影响而生理变化较小,并且还维持较低的膜脂过氧化水平,这可能是根能维持正常的吸水输水功能并在沙埋处理过程中和沙埋后地上叶片快速生长摆脱沙埋的重要物质基础。