Effects of Exogenous Spermidine on Antioxidant System Responses of Typha latifolia L. Under Cd^2＋ Stress

The effects of foliar spraying with spermidine (Spd), ranging in concentration from 0.25 to 0.50 mmol/L, on the antioxidant system under Cd^2 stress (range 0.1- 0.2 mmol/L Cd^2 ) in Typha latifolia L. grown hydroponically were investigated in order to offer a referenced evidence for an understanding of the mechanism by which polyamines (PAs) relieve the damage to plants by heavy metal and improve the phytoremediation efficiency of heavy metal-contaminated water. The results showed that Cd^2 stress induced oxidative injury, as evidenced by an increase in the generation of superoxide anion (O2), as well as the hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents in both leaves and caudices. With the exception of superoxide dismutase (SOD) activity in the leaves, an increase in the activities of catalase (CAT), guaiacol peroxidase (GPX), and glutathione reductase (GR) was observed in both leaves and caudices, SOD activity was increased in caudices, and ascorbate peroxidase (APX) activity was increased in leaves following Cd^2 treatment. The reduced glutathione (GSH) content in both leaves and caudices and the reductive ascorbate content in leaves was obviously increased, which were prompted by the application of exogenous Spd. Spraying with Spd increased the activity of GR and APX in both leaves and caudices, whereas the activity of SOD, CAT, and GPX was increased only in caudices following spraying with Spd. The generation of O2 and the H2O2 and MDA content in both leaves and caudices decreased after spraying with Spd. The decrease in MDA was more obvious following the application of 0.25 than 0.50 mmol/L Spd. It is supposed that exogenous Spd elevated the tolerance of T. latifolia under Cd^2 stress primarily by increasing GR activity and the GSH level.     

The Effects of Water Stress on Photosystem Ⅱ in Wheat

The fluorescence yield at room temperature, the capacity of excitation energy distribution between photosystem Ⅰ and Ⅱ by Mg2+, variable fluorescence yield, variable fluorescence quenching rate and fluorescence complementary area were decreased under water stress. These indicated that photosystem Il was impaired. The inhibited variable fluorescence yield could be partly recovered by the addition of artificial electron donor DPC. Therefore, water stress inhibited not only the oxidizing site of photosystem Ⅱ but also impaired partly the reaction center of photosystem Ⅱ.     

Effect of Exogenous ABA on the Salt Tolerance of Corn Seedlings Under Salt Stress

The exogenous ABA in different concentrations was used to spray Zea mays L. (cv. Luyu 11) seedlings under different salinity. The growth status, osomotic potential and osmotic regulatory activity, the contents of Na+ and K+, soluble sugars and proline were determined at different time after treatment. The results were shown as follows: The exogenous ABA gave an increase in salt resistance and dry weight of corn seedlings under different salinity, this increase was as a result of inhanced osmotic adjustment activity and exclusion of sodium ions from the shoot through the action of exogenous ABA, resulting an accumulation of sodium in the roots. Moreover, the decrease of osmotic potential and the increase of osmotic regulatory activity were for reasons of enhancement of organic osmotors, instead inorganic, e.g. Na+ and K+ osmotors. The mechanism of sodium exclusion from the shoot was also discussed.     

Effects of Exogenous Nitric Oxide on Photochemical Activity of Photosystem Ⅱ in Potato Leaf Tissue Under Non-stress Condition

Under non-stress condition, effects of exogenous nitric oxide (NO) on chlorophyll fluorescence parameters in detached leaves and leaf discs of potato (Solanum tuberosum L.) were surveyed. Results showed that the maximal quantum efficiency (Fv/Fm) and the effective quantum efficiency (F P_SⅡ) of photosystem Ⅱ (PSⅡ) were reduced by exogenous NO under illumination (150 mmol.m^-2.s^-1, 25 ℃). This influence was related not only to the concentration of sodium nitroprusside (SNP, a NO donor) solution, but also to the active duration of NO on leaf tissue. Results with leaf discs showed that the effects of SNP on F P_SⅡ could be prevented by bovine hemoglobin (a powerful NO scavenger), while a mixture of NO^2- and NO^3- (the decomposition product of NO or its donor SNP) had much less influence on F P_SⅡ than SNP, indicating that effects of exogenous SNP on PSⅡ photochemical activity was mainly due to NO generation. Under light (150 mmol.m^-2.s^-1, 25 ℃) for 4 h or longer period, the non-photochemical quenching (NPQ) in SNP-soaked leaves was statistically similar to that in H₂O-soaked control, but F P_SⅡ and the proportion of open reaction centers (measured as qP) were lower than control, respectively. After 25 min dark-adaptation, the maximal fluorescence (Fm) in SNP treatment (8 and 12 h illumination duration) was significantly lower than the control, while the initial fluorescence (F_o) in SNP and H₂O-treated leaves had no significant difference. Therefore this indicated that under the present experimental condition, the NO-affected site might not be the PSⅡ reaction centers. On the donor side of PSⅡ, NO putatively influenced the light-harvesting capacity of leaves under light; on the acceptor side, NO-affected sites were some components of electron transport chain after Q_A, i.e. NO enhanced the reductive degree of reaction centers through blocking the electron transport after Q_A, thus reducing the photochemical activity of PSⅡ.     

Effects of Exogenous γ-Aminobutyric Acid (GABA) on Photosynthesis and Antioxidant System in Pepper (Capsicum annuum L.) Seedlings Under Low Light Stress

The effects of γ-aminobutyric acid (GABA) treatment on parameters of photosynthesis and antioxidant defense system were measured in pepper (Capsicum annuum L.) leaves under low-light (LL) stress. Seedlings exposed to LL stress showed increased chlorophyll content as well as decreased net photosynthetic rate (P _n), stomatal conductance (g _s), maximum quantum yield of PSII (F _v/F _m), actual PSII photochemical efficiency (Φ_PSII), electron transport rates and photochemical quenching coefficient (q _p). However, almost all the photosynthetic parameters above were enhanced markedly in seedlings treated with GABA under LL stress. Moreover, LL stress increased malondialdehyde (MDA) content, superoxide anion radical (O₂ ^·?) and hydrogen peroxide (H₂O₂) production. GABA-treated, LL-stressed seedlings exhibited lower MDA, O₂ ^·? and H₂O₂ production, and showed an activated antioxidant defense system, including increased activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, ascorbate and glutathione. Moreover, seedlings subjected to LL stress showed increased endogenous GABA levels, and the level was further improved by application of exogenous GABA. These results suggest that GABA mitigates the LL-induced stress via regulating the antioxidant defense system and maintaining a high level of photochemical efficiency in pepper seedlings.

     

Photosynthetic Properties of Photosystem Ⅱ in Arabidopsis thaliana Ipa1 Mutant

In a previous study, we characterized a high chlorophyll fluorescence Ipal mutant of Arabidopsis thallana, in which approximately 20% photosystem （PS） Ⅱ protein is accumulated. In the present study, analysis of fluorescence decay kinetics and thermoluminescence profiles demonstrated that the electron transfer reaction on either the donor or acceptor side of PSII remained largely unaffected in the Ipa1 mutant. In the mutant, maximal photochemical efficiency （Fv/Fm, where Fm is the maximum fluorescence yield and Fv is variable fluorescence） decreased with increasing light intensity and remained almost unchanged in wildtype plants under different light conditions. The Fv/Fm values also increased when mutant plants were transferred from standard growth light to low light conditions. Analysis of PSll protein accumulation further confirmed that the amount of PSll reaction center protein is correlated with changes in Fv/Fm in Ipal plants. Thus, the assembled PSll in the mutant was functional and also showed increased photosensitivity compared with wild-type plants.     

Does Seed Priming Induce Changes in the Levels of Some Endogenous Plant Hormones in Hexaploid Wheat Plants Under Salt Stress？

In order to assess whether salt tolerance could be Improved In spring wheat （Triticum aestivum L.）, the present study was performed by soaking the seeds of two cultlvars, namely MH-97 （salt sensitive） and Inqlab-91 （salt tolerant）, for 12 h In distilled water or 100 mol/m^3 CaCl2, KCI, or NaCI. Primed seeds from each treatment group and non-primed seeds were sown In a field In which NaCI salinity of 15 dS/m was developed. Priming of seeds with CaCl2, followed by priming with KCI and NaCI, was found to be effective In alleviating the adverse effects of salt stress on both wheat cultivars In terms of shoot fresh and dry weights and grain yield. Priming with CaCl2 alleviated the adverse effects of salt stress on hormonal balance In plants of both cultlvars. In MH-97 plants, CaCl2 pretreatment considerably reduced leaf absclslc acid （ABA） concentrations and Increased leaf free salicylic acid （SA） concentrations under both saline and non-saline conditions. In contrast, In the Inqlab-91 plant, CaCl2 Increased free Indoleacetic acid （IAA） and indolebutyrlc acid （IBA） content. However, priming of seeds with CaCl2 did not alter free polyamlne levels in either cultlvar, although spermldlne levels were considerably lower In plants raised from seeds treated with CaCl2 for both cultlvars under saline conditions. Priming with KCI Increased growth In Inqlab-91 plants, but not In MH-97 plants, under saline conditions. The salinity Induced reducUon In auxins （IAA and IBA） was alleviated by NaCI priming In both cultlvars under saline conditions. However, NaCI Increased leaf free ABA content and lowered leaf SA and putresclne levels In Inqlab-91 plants under saline conditions. In conclusion, although all three priming agents （I.e. CaCl2, KCI, and NaCI） were effective In alleviating the adverse effects of salt stress on wheat plants, their effects on altering the levels of different plant hormones were different In the two cuItlvars.     

Effect of “External” Superoxide Anion on Apoptosis in Coleoptiles of Wheat Seedlings

A derivative of phthalic acid, dibutylphthalate (DBP), which has gametocidal effect at the concentration of approximately 10(-4) M, increased apoptosis in coleoptiles of wheat seedlings. This was associated with activation of chromatin margination and generation of mitochondria-containing vesicles. At the same concentration, DBP activated the release by the coleoptiles of superoxide anion into the environment. Lower (10(-5) M) and higher (10(-3) M) concentrations of DBP virtually had no effect on either process. A probable mechanism of effect of the "external" superoxide anion on apoptosis within the plant cell is discussed.     

外源H2O2对盐胁迫下小麦幼苗生理指标的影响

以‘郑麦-004’小麦幼苗为供试材料,采用Hoagland营养液培养方法,通过添加H2O2的清除剂过氧化氢酶(CAT)和抗坏血酸(ASA),研究0.05μmol/L外源H2O2处理对150mmol/L NaCl胁迫下小麦幼苗生长和抗氧化系统活性的影响,探讨低浓度外源H2O2对盐胁迫下小麦幼苗伤害的防护作用及其生理机制。结果显示:外源H2O2能缓解盐胁迫对小麦幼苗生长的抑制效应,降低丙二醛(MDA)含量和超氧自由基(O2.-)的产生速率,使小麦幼苗的株高、根长和干重均显著增加,并能提高超氧化物歧化酶(SOD)、过氧化物酶(POD)、CAT、抗坏血酸氧化酶(APX)等保护酶活性和抗氧化物质谷胱甘肽(GSH)的含量;而H2O2清除剂(CAT和AsA)能够逆转外源H2O2对盐胁迫下小麦幼苗生长的促进作用。研究表明,低浓度外源H2O2处理能促进小麦幼苗中的酶类和非酶类抗氧化剂的产生,减少脂质过氧化物的含量,提高小麦幼苗的耐盐性。     

外源亚精胺对硝酸钙胁迫下小白菜生长与光合作用及其品质的影响

以小白菜品种‘寒笑’为实验材料,采用营养液栽培法,研究了80 mmol/L硝酸钙胁迫下,叶面喷施0.5mmol/L亚精胺(Spd)对小白菜生长、光合作用及其品质的影响。结果表明,(1)Ca(NO3)2胁迫显著抑制了小白菜幼苗生长,使植株的株高、根长、叶面积、根体积、干鲜重显著降低,而叶面喷施Spd可有效缓解胁迫对生长的抑制。(2)Ca(NO3)2胁迫处理植株叶绿素含量比正常营养液培养处理(对照)显著下降了54.72%,而叶面喷施Spd可以有效缓解Ca(NO3)2胁迫对光合色素含量的抑制,并且使植株类胡萝卜素含量比Ca(NO3)2胁迫处理显著提高53.33%。(3)Ca(NO3)2胁迫显著降低了小白菜幼苗光合作用效率,使植株净光合速率(Pn)比对照显著下降34.45%,而叶面喷施Spd可以有效缓解Ca(NO3)2胁迫对Pn的抑制,使植株Pn比Ca(NO3)2胁迫处理显著提高28.11%。(4)Ca(NO3)2胁迫显著降低了小白菜幼苗品质,其植株维生素C、可溶性糖、可溶性蛋白含量比对照显著降低,同期有机酸、硝酸盐含量却比对照显著升高,而叶面喷施Spd可以显著改善上述小白菜营养指标。研究认为,外源亚精胺可有效缓解Ca(NO3)2胁迫对小白菜生长和光合作用的抑制,提高Ca(NO3)2胁迫环境条件下小白菜的品质。     

外源亚精胺对盐胁迫下燕麦幼苗生长及生理特性的影响

为探讨外源喷施亚精胺(Spd)对燕麦幼苗生长和耐盐性的影响,该研究选用燕麦品种'白燕5号'为试验材料,通过水培试验研究70 mmol/L盐胁迫下(NaCl和Na2SO4摩尔比1∶1混合),叶面喷施不同浓度的亚精胺对燕麦幼苗生长、根系活力、抗氧化酶活性以及丙二醛、游离脯氨酸和离子含量的影响.结果 显示:(1)盐胁迫显著抑...     

外源精胺对水分胁迫下小麦幼苗保护酶活性的影响

通过营养液培养试验,研究了水分胁迫下外源精胺(Spm)对抗旱性不同的小麦品种幼苗叶片质膜相对透性及保护酶活性的影响.结果表明:水分胁迫下,小麦叶片的质膜相对透性、M DA含量增加、SOD、CAT和POD活性上升,外源精胺处理可延缓水分胁迫下小麦叶片质膜相对透性和M DA含量上升,提高了SOD、CAT、POD酶活性的上升幅度;并且对抗旱性弱的品种保护酶活性增幅高于抗旱性强的品种.因此,外源精胺处理对抗旱性弱的品种缓解水分胁迫作用大于抗旱性强的品种.     

叶面喷施亚精胺对高温胁迫下番茄叶绿素合成代谢的影响

以设施番茄栽培品种‘金棚朝冠’幼苗为试验材料,研究叶面喷施0.25 mmol·L~(-1)亚精胺(Spd)对高温胁迫下(38℃/28℃,昼/夜)番茄幼苗生长及叶绿素合成过程中前体物质含量、关键酶活性和叶绿素含量的影响,探讨Spd缓解番茄高温胁迫伤害的生理机制。结果表明:(1)高温胁迫显著抑制了番茄幼苗的生长,叶面喷施Spd可有效缓解高温胁迫对番茄幼苗地上部生长的抑制作用,但对于地下部的生长无显著缓解作用。(2)高温胁迫下番茄叶片叶绿素合成前体物质δ-氨基酮戊酸(ALA)和胆色素原(PBG)的含量显著提高,而尿卟啉原Ⅲ(UroⅢ)、原卟啉Ⅸ(ProtoⅨ)、镁-原卟啉Ⅸ(Mg-protoⅨ)和原叶绿素酸(Pchl)的含量显著降低,证明叶绿素前体由PBG向UroⅢ的转化受阻,导致叶绿素a(Chla)、总叶绿素(Chlt)含量和Chla/Chlb显著降低。(3)叶面喷施Spd能增强高温胁迫下胆色素原脱氨酶(PBGD)活性,有效缓解了高温胁迫对PBG到UroⅢ转化的阻碍作用,促进PBG之后叶绿素合成前体物质的合成,Chla含量和Chla/Chlb显著增加。研究发现,高温胁迫显著抑制番茄幼苗的生长,叶面喷施Spd可通过显著增强PBGD活性来缓解由PBG向UroⅢ的受阻程度,促进高温胁迫下番茄叶片的叶绿素前体合成,提高叶绿素含量和番茄植株的生长量,减轻高温胁迫对番茄幼苗生长的伤害。     

外源Spd预处理对甜瓜白粉病抗性及其内源多胺的诱导分析

以甜瓜感病品种‘0544’为试材,测定外源亚精胺(Spd)预处理和白粉病菌接种后甜瓜幼苗的光合参数、抗氧化酶活性、内源多胺含量及多胺合成与代谢相关基因表达等的变化,探讨外源Spd处理对甜瓜幼苗白粉病抗性的诱导作用机制。结果显示:(1)1.0mmol·L-1外源Spd处理可显著降低甜瓜幼苗的白粉病病情指数,缓解植株发病症状;(2)外源Spd处理可诱导甜瓜幼苗的多胺合成以及代谢相关基因(SAMDC、ADC、ODC、Spd、Spm、PAO)显著上调表达;(3)外源Spd处理可诱导甜瓜幼苗腐胺(Put)和Spd含量显著增加,而外源Spd并接种白粉病菌处理对甜瓜幼苗精胺(Spm)含量积累的诱导更加显著;(4)接种白粉病菌诱导了甜瓜幼苗的多酚氧化酶(PPO)、过氧化物酶(POD)和超氧化物歧化酶(SOD)的活性,外源Spd预处理后再接种白粉病的诱导作用更大,同时外源Spd处理还诱导了甜瓜幼苗过氧化氢(H_2O_2)含量的升高;(5)在观测期(120h)内,接种白粉病菌对甜瓜叶片的光合作用抑制较小,而外源Spd预处理并接种白粉病菌共同诱导了甜瓜幼苗的光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)的显著升高。研究认为,在外源Spd预处理甜瓜幼苗后再接种白粉病菌,甜瓜幼苗可以通过多胺的快速积累及代谢产生的H_2O_2来启动响应机制,进而通过增强防御酶活性等途径来提高对白粉病的抗性。     

外源亚精胺对荇菜抗Hg2+胁迫能力的影响

3 mg/L的Hg2降低了叶内亚精胺(spermidine,Spd)、精胺(spermine,Spm)含量,促进了腐胺(put resci ne,Put)合成,喷施Spd可提高叶内Spd、Spm含量,对Put含量则在低浓度下使其下降、高浓度(将近1mmo1/L)下使之上升.3mg/L的Hg2 可显著降低SOD、CaT、APx活性,提高02-产生速率,导致膜脂过氧化物(MDA)过量积累,造成叶绿素、可溶性蛋白大幅度下降.而喷施Spd可减轻Hg2 处理的这些作用,喷施的最适浓度为0.1～0.5 mmol/L.     

水分胁迫下小麦类脱水素基因表达的半定量RT-PCR分析

以‘郑引1号’小麦为材料,经水分胁迫后进行RT-PCR扩增,结果在胁迫条件下获得500bp的脱水素基因(wzy1-1)。利用半定量RT-PCR方法,分析‘陕合6号’和‘郑引1号’小麦在正常供水条件下及PEG6000胁迫后18、24和42h,以及复水6和12h时wzy1-1在叶片中的表达。结果表明:2个小麦品种中wzy1-1在水分胁迫后18h均有表达,至胁迫24、48h时表达量较18h均有所增多;复水6h后该基因表达迅速降低,至复水后12h表达消失。且该基因在‘陕合6号’(抗旱性较强)叶片中表达量较‘郑引1号’(抗旱性较弱)高,表明该基因的表达与小麦的抗旱性密切相关。     

He-Ne激光对水分胁迫下小麦幼苗生理特性的影响

用He-Ne激光(5.23×10-3W.mm-2)处理经不同浓度PEG6000胁迫的小麦幼苗,研究水分胁迫条件下激光辐照对小麦幼苗生理特性的影响。结果表明,He-Ne激光辐照可显著提高水分胁迫下小麦幼苗的根系活力以及抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性(P<0.05),并使其脯氨酸含量显著增加(P<0.05),而对其超氧化物歧化酶(SOD)的活性没有显著影响。可见,He-Ne激光可通过提高根系活力、抗氧化酶活性和脯氨酸含量来显著增强小麦幼苗的抗旱性。