不同耐盐性水稻幼苗根氨同化酶对盐胁迫的反应

在盐胁迫下,检测了耐盐性不同的水稻(Oryza sativa L.)品种根部氨同化酶及其相关参数的变化。结果表明,根的可溶性蛋白、谷氨酰胺合成酶(GS)及依赖于NADH的谷氨酸合酶(NADH-GOGAT)活性在高盐浓度下不同程度地降低,其影响大小依次为早花二号(盐敏感品种)、金珠一号(正常栽培品种)、津稻779(耐盐品种),与其耐盐性相一致。在盐胁迫条件下,在耐盐性较高的水稻品种中, GS和GOGAT活性比盐敏感品种高,NH4 浓度维持在较低的水平。Native-PAGE和活性染色结果表明,GSrb更容易受到外界环境的影响。在高浓度盐的胁迫下,早花二号、金珠一号的依赖于NADH的谷氨酸脱氢酶(NADH-GDH)活性都有较显著的升高,津稻779却无明显的变化,这和NH4 含量的变化相一致。盐不同程度地导致可溶性糖(TSS)在金珠一号和津稻779根部积累,而在早花2号的根部,可溶性糖的水平则随盐浓度的不同而表现出不同的变化。在所检测的品种中,脯氨酸的含量均有不同程度的升高,但在高盐浓度下,盐敏感品种的含量较低。这些结果提示,不同的水稻品种对盐胁迫的敏感程度与该品种GS以及GOGAT活性的高低有关。     

水稻种子萌发期间谷氨酰胺合成酶和NADH-谷氨酸合酶的变化

测定了水稻种子不同萌发时期胚乳、胚芽鞘和幼根的谷氨酰胺合成酶（GS）和依赖于NADH的谷氨酸合酶（NADH－GOGAT）活性变化。胚乳和胚芽鞘的GS活性在萌发过程中升高,幼根的GS活性则有所降低。NADH－GOGAT的活性变化趋势与GS相同。Native-PAGE活性染色表明,在萌发阶段的水稻种子胚乳和幼根里,始终只观察到一种GS活性带。但是,在水稻种子萌发3d后,在胚芽鞘中除继续检测到GS1的活性外,还可以观察到GS2的活性。蛋白质印迹显示,水稻种子胚乳中的GS（GSe)和GS1和GSra一样是一种胞质型GS。实验结果提示,这些不同组织中的GS与NADH－GOGAT构成的循环途径也许是水稻种子萌发时氨同化的主要途径。     

外源亚精胺对盐胁迫下黄瓜幼苗体内抗氧化酶活性的影响

以不同耐盐性黄瓜品种“长春密刺”和“津春2号”为材料,采用营养液栽培,研究了外源亚精胺(Spd)对NaCl胁迫下黄瓜幼苗叶片与根系中超氧阴离子(O2-.)产生速率、超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性的影响。结果表明,外源Spd对未经盐胁迫处理(对照)黄瓜幼苗体内O2-.产生速率、SOD、CAT和POD活性均无显著性影响;盐胁迫处理提高了O2-.产生速率,SOD、POD和CAT活性都有不同程度的升高;外源Spd处理进一步提高了盐胁迫下SOD、POD和CAT活性,减缓了O2-.产生速率。与耐盐型“长春密刺”品种相比,盐胁迫对盐敏感型“津春2号”影响较大,外源Spd对盐敏感型黄瓜品种盐胁迫伤害的缓解作用较大。表明盐胁迫下外源Spd可缓解盐胁迫对膜的伤害,从而提高黄瓜幼苗的耐盐性。     

不同黄瓜品种种子萌发期的耐盐性研究

在不同浓度的NaCl胁迫盐境下发芽,对黄瓜种子萌发有显著影响,随着NaCl胁迫浓度增大,对种子萌发的抑制作用明显增强,种子活力指数、发芽指数、幼胚一级侧根数比发芽率对NaCl胁迫的反应更敏感.在供试的14个黄瓜品种中,不同黄瓜品种种子萌发受盐胁迫抑制的程度不同,其中耐盐品种有中农12号和津春5号,新秀2号和津优1号为不耐盐品种,其他为耐盐性中等品种.     

快生型大豆根瘤菌的渗透调节

弗雷德中华根瘤菌(Sinorhizobium fredii)RT 19是快生型大豆根瘤菌。该菌株在不同浓度NaCl条件下,其细胞内的游离谷氯酸和钾离子含量随盐浓度的提高而急剧增加。在无盐和低浓度NICl条件下,测不出细胞内有游离苏氨酸,但在较高浓度盐存在时,其含量也随着盐浓度的提高而递增。RT19在对数生长后期,突然加入NaCl,使其培养液中的NaCl的最终浓度达到300mmol／L,定时取样测定细胞内氨基酸含量,发现5分钟后谷氨酸含量急剧上升,比不加盐的对照高出5倍,而且在3小时内保持不变．苏氨酸也出现类似情况。测定了RT 19及其转化子RTt1 9和gTt50的谷氨酸脱氢酶(GDH)、谷氨酰胺合成酶(GS)和谷氨酸合成酶(GOGAT)在盐压下的活性,发现在300 mmol／L NaCl或300mm。I／L KC1存在时,GDH酶活性稍为下降或不变,而GS和GOGAT酶活性则显著提高。     

盐胁迫对海岛棉和陆地棉幼苗生长及生理特性的影响

采用盆栽法,以海岛棉(Gossypium barbadense)品种新海21号、新海34号和陆地棉(G.hirsutum)品种新陆早50号、新陆早57号为材料,探讨了盐胁迫下海岛棉和陆地棉植株的生长、叶绿素含量、净光合速率、蒸腾速率、抗氧化酶活性、渗透调节物质及丙二醛含量变化的差异。结果显示,随着盐浓度的增加,4个供试品种幼苗的生长、叶绿素含量、净光合速率、蒸腾速率均呈不同程度的下降,而过氧化物酶、超氧化物歧化酶及可溶性糖含量随着盐浓度的增加呈先增后降的趋势,脯氨酸和丙二醛含量均上升。不同品种之间,新海21号和新海34号受胁迫的影响程度小于新陆早57号和新陆早50号。在0.6%Na Cl胁迫下,海岛棉和陆地棉品种均表现出较好的耐盐性。而0.8%和1.0%的Na Cl胁迫对4个供试品种的生长抑制作用大,导致新陆早57号和新陆早50号幼苗生长缓慢、叶面积小、干物质积累少甚至死苗。在较高浓度的盐胁迫下,棉花品种幼苗第1片真叶展开受到显著抑制,可以作为棉花耐盐品种的筛选指标。     

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.     

NaHSO3对盐胁迫下小麦幼苗氮同化酶及脯氨酸含量的影响

以普通小麦(Triticum aestivumL.)为材料,研究了NaHSO3对不同盐度胁迫下小麦幼苗氮素同化酶和脯氨酸含量的调节。结果表明,盐胁迫降低了叶片中硝酸还原酸(NR)的活性,加入NaHSO3之后,NR活性表现出进一步的降低。谷氨酰胺合成酶(GS)在低浓度盐胁迫下活性增加,在高浓度盐胁迫下活性降低;NaHSO3加入时,即便在低盐浓度下GS活性也降低。依赖于NADH的谷氨酸脱氢酶(NADH-GDH)和依赖于NADP的异柠檬酸脱氢酶(NADP-ICDH)的变化趋势一致,在盐胁迫下它们的活性都明显增加;NaHSO3加入促进了它们活性的进一步增加,尤其对NADH-GDH活性的促进更为明显。游离脯氨酸在高浓度盐胁迫下大量积累,在低浓度盐胁迫下含量增加不明显;NaHSO3促进了盐胁迫下脯氨酸的积累,提示了NaHSO3促进了盐胁迫下小麦幼苗碳氮营养元素的贮存。     

叶施NO对NaCl胁迫下红砂幼苗叶片和根系中氮代谢酶及营养物质的影响

以当年生红砂(Reaumuria soongorica)幼苗为材料,采用盆栽实验,考察叶面喷施不同浓度(0、0.01、0.10、0.25、0.50、1.00 mmol·L^-1)NO供体硝普钠 (SNP) 对NaCl(300 mmol·L^-1)胁迫下红砂根、叶中可溶性蛋白、游离氨基酸和硝态氮含量,以及谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)、硝酸还原酶(NR)活性的影响,并采用主成分分析和隶属函数法筛选NO对NaCl胁迫缓解效应的氮代谢指标和最佳NO浓度,以探讨外源NO对NaCl 胁迫下红砂缓解效应的氮代谢响应机制。结果表明：(1)在300 mmol·L^-1 NaCl胁迫处理下,红砂幼苗根、叶中可溶性蛋白、硝态氮含量以及GS、GOGAT、NR活性均比对照显著下降。(2)外源NO能显著提高盐胁迫下红砂叶、根中GS、GOGAT、NR活性和硝态氮含量,增加根中可溶性蛋白和游离氨基酸含量。(3)NR和GOGAT活性可用于评价NO对NaCl胁迫下红砂幼苗的缓解作用,外源NO(SNP)对红砂幼苗在NaCl胁迫下的缓解效果强弱表现为0.25 mmol·L^-1> 0.50 mmol·L^-1> 0.10 mmol·L^-1> 1.00 mmol·L^-1> 0.01 mmol·L^-1。研究发现,300 mmol·L^-1 NaCl胁迫显著抑制了红砂幼苗氮代谢,外源NO(SNP)有助于提高盐胁迫下红砂NR活性,加快硝态氮转化为铵态氮,促进红砂叶片和根中GS/GOGAT对转化物的同化,从而增强红砂幼苗的耐盐性,并以0.25 mmol·L^-1SNP处理时缓解作用最佳;NR和GOGAT活性可作为NO缓解盐胁迫的评价指标。     

水稻分蘖期耐盐性鉴定评价方法确立及种质筛选

分蘖期是水稻由秧田生长向本田生长过渡的营养生长关键时期。在盐渍化土壤上种植水稻,分蘖期耐盐性对水稻能否正常生长至关重要。合适的耐盐性鉴定方法是水稻耐盐种质筛选的前提。本研究目的在于通过水稻分蘖期盐浓度梯度筛选试验,明确水稻分蘖期耐盐性鉴定最适盐胁迫浓度和调查时间;利用确立的鉴定方法,筛选出水稻分蘖期耐盐种质。本研究选取具有不同程度耐盐性的26份水稻品种,于2015年和2016年分别在10个和7个盐浓度梯度下,以盐害等级为分蘖期耐盐评价指标,开展水稻分蘖期耐盐性鉴定评价试验。结果表明,在0.5%盐浓度下,处理4～6周后供试种质的盐害等级差异表现为最大,因此认为0.5%盐浓度是水稻分蘖期耐盐性鉴定的最适盐胁迫浓度,盐处理后4～6周是水稻分蘖期盐害等级调查的最佳调查时间。参照国际水稻所提出的水稻分蘖期耐盐性评价标准,本研究对其进行了改进,提出以单株为单位进行水稻分蘖期耐盐性评价方法,利用平均盐害等级评估分蘖期耐盐性。该方法能够方便、准确地评价水稻耐盐性强弱。依据上述确立的水稻分蘖期耐盐性鉴定评价方法,本研究于2017-2019年期间对2886份来自不同生态区域的水稻种质进行分蘖期耐盐性鉴定评价,鉴定筛选出137份耐盐种质,为水稻耐盐遗传机制和育种研究提供资源支撑。     

盐胁迫下水稻叶绿体中Na~ 、Cl~-积累导致叶片净光合速率下降

研究了 0～ 2 0 0mmol/L的NaCl胁迫下耐盐性不同的水稻品种Pokkali(耐盐 )和Peta(盐敏感 )根系、叶片和叶绿体中Na 、K 和Cl-含量的变化及其与叶片光合作用的关系。结果表明 :随着NaCl胁迫时间和浓度的增加 ,供试 2个品种在根、叶片和叶绿体中Na 、Cl-含量增加 ,K 含量下降。耐盐品种体内Na 、Cl-含量增加或K 含量减少的幅度小于盐敏感品种。在 2 0 0mmol/L的NaCl胁迫下盐敏感品种根、叶片和叶绿体中的Na /K 分别是耐盐品种的 2 0 8%、30 8%和 2 97%。与Na 相比 ,耐盐品种根系对K 的吸收和向叶片运输的选择性 (SK ,Na)较强。但在经过0、10 0和 2 0 0mmol/L的NaCl处理后 2个品种叶绿体中的Na /K 均高于叶片 (SK ,Na均小于 1)。盐胁迫下水稻叶绿体中Na 、Cl-含量和Na /K 与叶片净光合速率呈极显著负相关。     

盐胁迫下水稻叶绿体中Na+、Cl-积累导致叶片净光合速率下降

研究了0-200mmol/L的NaCl胁迫下耐盐性不同的水稻品种Pokkali(耐盐）和Peta(盐敏感）根系,叶片和叶绿体中Na^ ,K^ 和Cl^-含量的变化及其与叶片光合作用的关系。结果表明：随着NaCl胁迫时间和浓度的增加,供试2个品种在根,叶片和叶绿体中Na^ ,Cl^－含量增加,K^ 含量下降。耐盐品种体内Na^ ,Cl^－含量增加或K^ 含量减少的幅度小于盐敏感品种。在200mmol/L的NaCl胁迫下盐敏感品种根,叶片和叶绿体中的Na^ /K^ 分别是耐盐品种的208％,308％和297％。与Na^ 相比,耐盐品种根系对K^ 吸收和向叶片运输的选择性（SK,Na)较强。但在经过0,100和200mmol/L的NaCl处理后2个品种叶绿体中的Na^ /K^ 均高于叶片（SK,Na均小于1）。盐胁迫下水稻叶绿体中Na^ ,Cl^-含量和Na^ /K^ 与叶片净光合速度呈极显著负相关。     

Phenolic content and antioxidant activity in two contrasting Medicago ciliaris lines cultivated under salt stress

The objective of this study was to determine more indepth physiological and antioxidant responses in two Medicago ciliaris lines (a salt-tolerant line TNC 1.8 and a salt-sensitive line TNC 11.9) with contrasting responses to 100 mM NaCl. Under salt stress, both lines showed a decrease in total biomass and in the growth rate for roots, but TNC 1.8 was less affected by salt than TNC 11.9 in that it maintained leaf growth even in the presence of added salt. In both lines, salt stress mainly affected micronutrient status (Fe, Mn, Cu and Zn) rather than K nutrition, but the tolerant line TNC 1.8 accumulated more Na in leaves and less in roots compared with TNC 11.9. Salt stress decreased total soluble sugars (TSS) in all organs of the sensitive line TNC 11.9, whereas TSS was only reduced in roots of the tolerant line. The salt-induced drop in growth was linked to an increase in lipid peroxidation in roots of both lines and in leaves of the sensitive line. The salt-tolerant line TNC 1.8 was more efficient at managing salt-induced oxidative damage in leaves and to a lesser extent in roots than the salt-sensitive line TNC 11.9, by preserving higher phenolic compound and superoxide dismutase levels in both organs.     

Potassium nitrate application alleviates sodium chloride stress in winter wheat cultivars differing in salt tolerance

A sand culture experiment was conducted to answer the question whether or not exogenous KNO(3) can alleviate adverse effects of salt stress in winter wheat by monitoring plant growth, K(+)/Na(+) accumulation and the activity of some antioxidant enzymes. Seeds of two wheat cultivars (CVs), DK961 (salt-tolerant) and JN17 (salt-sensitive), were planted in sandboxes and controls germinated and raised with Hoagland nutrient solution (6 mM KNO(3), no NaCl). Experimental seeds were exposed to seven modified Hoagland solutions containing increased levels of KNO(3) (11, 16, 21 mM) or 100 mM NaCl in combination with the four KNO(3) concentrations (6, 11, 16 and 21 mM). Plants were harvested 30 d after imbibition, with controls approximately 22 cm in height. Both CVs showed significant reduction in plant height, root length and dry weight of shoots and roots under KNO(3) or NaCl stress. However, the combination of increased KNO(3) and NaCl alleviated symptoms of the individual salt stresses by improving growth of shoots and roots, reducing electrolyte leakage, malondialdehyde and soluble sugar contents and enhancing the activities of antioxidant enzymes. The salt-tolerant cultivar accumulated more K(+) in both shoots and roots compared with the higher Na(+) accumulation typical for the salt-sensitive cultivar. Soluble sugar content and activities of antioxidant enzymes were found to be more stable in the salt-tolerant cultivar. Our findings suggest that the optimal K(+)/Na(+) ratio of the nutrient solution should be 16:100 for both the salt-tolerant and the salt-sensitive cultivar under the experimental conditions used, and that the alleviation of NaCl stress symptoms through simultaneously applied elevated KNO(3) was more effective in the salt-tolerant than in the salt-sensitive cultivar.     

Control of glutamate dehydrogenase from Pisum sativum roots

-Glutamate dehydrogenase (GDH) was found in soluble and particulate (mitochondrial) fractions of pea roots. The activity of NADH-dependent GDH in fresh mitochondrial extract was increased about 10-fold by addition of zinc, manganese or calcium, but high concentrations of zinc were inhibitory. During storage, GDH activity of the mitochondrial extract slowly increased. The NADH activity was inhibited by citrate and other chelating agents. NADH-dependent reductive amination was also inhibited by glutamate, the product of the reaction; by contrast NADPH dependent activity was relatively unaffected by zinc, chelating agents or glutamate. Sensitivity (of NADH-GDH) to glutamate was lost on purification, but was restored when the enzyme was immobilized by binding to an insoluble support (AE cellulose). Glutamate appears to change the affinity of the enzyme for 2-oxoglutarate.     

Nitrogen uptake and metabolism in Populus x canescens as affected by salinity

External salinization can affect different steps of nitrogen (N) metabolism (ion uptake, N assimilation, and amino acid and protein synthesis) depending on the inorganic N source. Here, we assessed the net uptake of N supplied as nitrate or ammonium and N assimilation (combining metabolite analyses with molecular biological approaches) in grey poplar (Populus x canescens) plants grown under saline (75 mM NaCl) and control conditions. The specific (micromol N g(-1) dry weight fine roots h(-1)) and total plant (micromol N per plant h(-1)) N net uptake rates, total plant N content, total plant biomass and total leaf protein concentration were reduced under saline conditions when plants were supplied with ammonium. In both nutritional groups, salt treatment caused pronounced accumulation of soluble N compounds in the leaves. The mRNAs of genes coding for enzymes catalyzing rate-limiting steps of both proline synthesis and degradation (delta-1-pyrroline-5-carboxylate synthase and proline dehydrogenase) as well as for NADH-dependent glutamate synthase were accumulated under saline conditions. Whereas under control conditions the plant N status seemed to be superior when ammonium was supplied, the N balance of ammonium-fed plants was more severely affected by salt stress than that of plants supplied with nitrate. Possible metabolic implications of stress-related accumulation of particular amino acids are discussed.     

NaCl effects on proline metabolism in rice (Oryza sativa) seedlings

Salt-stress effects on osmotic adjustment, ion and proline concentrations as well as proline metabolizing enzyme activities were studied in two rice ( Oryza sativa L.) cultivars differing in salinity resistance: I Kong Pao (IKP; salt-sensitive) and Nona Bokra (salt-resistant). The salt-sensitive cultivar exposed to 50 and 100 m M NaCl in nutritive solution for 3 and 10 days accumulated higher levels of sodium and proline than the salt-resistant cultivar and displayed lower levels of osmotic adjustment. Proline accumulation was not related to proteolysis and could not be explained by stress-induced modifications in Δ¹-pyrroline-5-carboxylate reductase (P5CR; EC 1.5.1.2) or proline dehydrogenase (PDH; EC 1.5.1.2) activities recorded in vitro. The extracted ornithine Δ -aminotransferase (OAT; EC 2.6.1.13) activity was increased by salt stress in the salt-sensitive cultivar only. In both genotypes, salt stress induced an increase in the aminating activity of root glutamate dehydrogenase (GDH; EC 1.4.1.2) while deaminating activity was reduced in the leaves of the salt-sensitive cultivar. The total extracted glutamine synthetase activity (GS; EC 6.3.1.2) was reduced in response to salinity but NaCl had contrasting effects on GS1 and GS2 isoforms in salt-sensitive IKP. Salinity increased the activity of ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) extracted from leaves of both genotypes and increased the activity of NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in the salt-sensitive cultivar. It is suggested that proline accumulation is a symptom of salt-stress injury in rice and that its accumulation in salt-sensitive plants results from an increase in OAT activity and an increase in the endogenous pool of its precursor glutamate. The physiological significance of the recorded changes are analyzed in relation to the functions of these enzymes in plant metabolism.     

High temperature effects on ammonium assimilation in leaves of two Festuca arundinacea cultivars with different heat susceptibility

The aim of this study was to determine the effects of high temperature stress on ammonium assimilation in leaves of two tall fescue cultivars (Festuca arundinacea), Jaguar 3 brand (J3) (heat-tolerant) and TF 66 (T6) (heat-sensitive). High temperature stress for either 10 d or 20 d, and particularly the 20 d stress, produced dramatic changes in ammonium assimilation. After 20 d of stress treatment, the accumulations of total nitrogen, nitrate, soluble protein and total free amino acid (20 amino acids) decreased in both cultivars. Moreover, the activities of main regulatory enzymes, such as nitrate reductase, glutamine synthetase (GS), NADH-dependent glutamate synthase (GOGAT), as well as Δ¹-pyrroline-5-carboxylate reductase (P5CR), also decreased in both cultivars when exposed to 20 d stress. Heat stress had little influence on ammonium accumulation in J3, but this was not the case with T6. The accumulations of nitrate, ammonium, soluble protein, and total free amino acid between the two cultivars were different. This suggests that accumulations of these nitrogen forms were associated with heat tolerance in both tall fescue cultivars. Changes of both NADH-glutamate dehydrogenase (NADH-GDH) activity and Glx (glutamine and glutamic acid) concentration in both cultivars indicated that there is an alternative system for assimilation of nitrogen through glutamate dehydrogenase (GDH) in T6 during longer high temperature stress periods. Our results provide an insight to further selection and breeding of heat-tolerant tall fescue turfgrass cultivars.     

Influence of host genotypes on growth,symbiotic performance and nitrogen assimilation in faba bean (Vicia faba L.) under salt stress

Fifteen genotypes of faba bean (Vicia faba L.) were inoculated with salt-tolerant Rhizobium leguminosarum biovar. viciae strain GRA 19 in solution culture with 0 (control) and 75 mM NaCl added immediately after transplanting. Genotypes varied in their tolerance of high levels of NaCl. Physiological parameters (dry weight of shoot and root, number and dry weight of nodules) were not affected by salinity in lines VF46, VF64 and VF112. Faba bean line VF60 was sensitive to salt stress. Host tolearance appeared to be a major requisite for nodulation and N₂ fixation under salt stress. Tolerant line VF112 sustained nitrogen fixation under saline conditions. Activity of the ammonium assimilation enzymes glutamine synthetase and glutamate synthase, and soluble protein content, were reduced by salinity in all genotypes tested. Evidence presented here suggests a need to select faba bean genotypes that are tolerant to salt stress.Abbreviations ARA acetylene reduction activity - NADH-GOGAT NADH-dependent glutamate synthase - GS glutamine synthetase