Promotion of 5-aminolevulinic acid treatment on leaf photosynthesis is related with increase of antioxidant enzyme activity in watermelon seedlings grown under shade condition

Watermelon [Citrullus lanatus (Thunb.) Mansfeld] is a photophilic plant, whose net photosynthetic rate was significantly decreased when seedlings were grown under low light condition. However, treatment with 100 mg kg⁻¹ 5-aminolevulinic acid (ALA) could significantly restore the photosynthetic ability under the environmental stress. The parameters of leaf gas exchange, chlorophyll modulated fluorescence and fast induction fluorescence of the ALA-treated plants were higher than that of the control. Additionally, ALA treatment increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Nevertheless, the treatment of diethyldithiocarbamate (DDC), an inhibitor of SOD activity, dramatically depressed photosynthesis of watermelon leaves, while ALA could reverse the inhibition of DDC. Therefore, it can be deduced that ALA promotion on photosynthesis of watermelon leaves under low light stress is attributed to its promotion on antioxidant enzyme activities, and the increased activities of the enzymes, which are mainly located near the reaction centers of PSI, can scavenge superoxide anions, leading to an increase of apparent electron transport rate and an alleviation of photosynthetic photoinhibition under the stressed environment.     

Role of 5-aminolevulinic acid on growth,photosynthetic parameters and antioxidant enzyme activity in NaCl-stressed <Emphasis Type="Italic">Isatis indigotica</Emphasis> Fort.

5-aminolevulinic acid (ALA) is a key precursor for the biosynthesis of porphyrins such as heme and chlorophyll. ALA alleviates salinity stress damage in germinating seeds and improves seedling growth. Exogenous application of ALA at low concentrations has been shown to enhance salt tolerance in a number of plants. In the present study, we studied the effect of exogenous application of ALA on enhancing salt stress tolerance in Isatis indigotica Fort. (Anhui population as S1, Shanxi population as S2). A foliar application of 0, 12.5, 16.7, 25.0, and 50.0 mg/L ALA was given to the leaves of I. indigotica plants treated with 100 mmol/L NaCl. The fresh weight of leaves and roots; chlorophyll relative content (SPAD value); photosynthetic parameters, such as net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular carbon dioxide concentration (Ci) and water use efficiency of the treated plants were determined. The third leaf of each treated plant was used to determine the activities of antioxidant enzymes. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutamate synthase (GOGAT), nitrate reductase (NR) activities and the malondialdehyde (MDA) content increased in response to 100 mmol/L NaCl in both S1 and S2 plants. However, the fresh weight of leaf and root, chlorophyll relative content, Pn, Gs, Ci decreased in response to salt stress in both S1 and S2 plants. In all foliar application of ALA in S1 plants, the MDA content, and the activities of SOD and POD were the highest in response to 50.0 mg/L foliar application of ALA. GOGAT and NR activities were the highest in response to 16.7 mg/L foliar ALA. Chlorophyll content and Pn were the highest in S1 plants treated with by 25.0 mg/L ALA. In S2 plants, plant fresh weight, chlorophyll relative content, SOD, CAT, NR activities and Pn treated with 16.7 mg/L ALA were higher than that of the control (CK0). POD, MDA, GOGAT activities in S2 plants treated with 25.0 mg/L ALA were the highest among all treatments. Thus, our results showed that the optimal concentration of ALA (16.7 ~ 25.0 mmol/L) increases the activity of antioxidant enzymes, which in turn helps to abate the damage caused by salt stress in I. indigotica seedlings. Furthermore, ALA also results in an increase in chlorophyll content, Pn and the activities of GOGAT and NR.     

5-氨基乙酰丙酸对NaCl胁迫下番茄幼苗光合特性的影响

为探讨5-氨基乙酰丙酸（ALA）对NaCl胁迫下番茄光合特性的调控作用,以‘金鹏一号’番茄幼苗为试材,研究叶面喷施50 mg·L^-1或根施10 mg·L^-1 ALA对100 mmol·L^-1 NaCl胁迫下番茄幼苗光合及叶绿素荧光参数的影响.结果表明： NaCl胁迫下,番茄幼苗光合气体交换参数（净光合速率P_n、气孔导度g_s、胞间CO₂浓度C_i、蒸腾速率T_r）及叶绿素荧光参数（实际光化学量子产量F_v′/F_m′、F_m′、PSⅡ反应中心实际光化学效率Φ_PSⅡ、表观光合电子传递效率ETR、光化学淬灭q_P、光化学反应Pc）均显著降低,根施或叶施ALA均可以提高NaCl胁迫下番茄叶片的光合能力,但两种处理方式之间存在一定差异.叶面喷施50 mg·L^-1ALA或根施10 mg·L^-1ALA处理均显著提高了番茄叶片P_n、T_r、g_s和C_i,提高了水分利用效率（WUE）,显著增加了NaCl胁迫下叶片的最大净光合速率,减轻了光抑制.根施ALA对叶绿素含量的作用效果较好,而叶施ALA对光合参数的作用效果较好,两处理叶绿素荧光参数差异不显著.叶面喷施或根施ALA可以提高番茄幼苗的耐盐性,其调控作用与促进叶绿素合成与稳定、维持正常气孔开闭、降低气孔限制,进而提高NaCl胁迫下番茄叶片的光合能力和PSⅡ光化学效率有关.
     

低浓度NaCl对玉米幼苗光合作用的影响

以Hoagland溶液为基础培养液,采用沙培法,研究了0,5,10,20,30mmol／LNaCl对玉米（Zeamays）幼苗光合作用的影响。结果表明,低浓度NaCl（5,10mmol／LNaCl）处理使其叶绿素含量增加,Chla／Chlb增大,PEPCase活性提高,光合速率增强。说明低盐促进玉米的光合作用可能与叶绿素含量增加,Chla／Chlb增大以及PEPCase活性提高有关。     

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～ 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。     

盐胁迫下囊果碱蓬出苗状况及苗期抗盐性

研究了盐胁迫对囊果碱蓬出苗、幼苗生长、离子积累以及光合放氧速率的影响.囊果碱蓬生长的最适盐浓度在200 mmol/L NaCl左右.高浓度NaCl(400 mmol/L和600 mmol/L)没有显著降低其出苗率,200 mmol/L NaCl对出苗率具有促进作用.400 mmol/L和600 mmol/L NaCl显著降低了光合放氧速率.囊果碱蓬在高浓度NaCl处理下能够维持叶片较高的K+/Na+ 及含水量可能是其适应高盐生境的重要机制.     

外源5-氨基乙酰丙酸对NaCl胁迫下黑果枸杞幼苗生理及生长的影响

5-氨基乙酰丙酸(ALA)是植物血红素、叶绿素等四吡咯化合物的关键生物合成前体,对植物适应非生物胁迫至关重要。为验证外源ALA对黑果枸杞幼苗生理生长的影响,该研究用300 mmol·L^-1 NaCl和不同浓度(0、5、10、15、20、25 mg·L^-1)的ALA共同处理黑果枸杞幼苗,并测定其相关的生理指标和生长指标,综合评价各处理幼苗的耐盐性。结果表明：(1)NaCl胁迫使黑果枸杞幼苗总生物量和叶片总叶绿素、类胡萝卜素、可溶性糖含量以及过氧化物酶(POD)活性较CK分别显著降低了33.39%、19.06%、24.38%、39.57%和47.91%(P<0.05),使黑果枸杞幼苗脯氨酸和丙二醛的含量较CK分别显著增加了165.74%和49.16%。(2)当外源ALA和NaCl同时处理时,黑果枸杞幼苗叶片类胡萝卜素和丙二醛含量、POD和过氧化氢酶(CAT)活性以及株高、总生物量均恢复至对照水平,叶片总叶绿素和脯氨酸含量以及SOD活性较CK显著增加。(3)黑果枸杞幼苗叶片叶绿素和脯氨酸含量以及抗氧化酶活性、生物量等指标随ALA浓度增加均呈先...     

Enhanced susceptibility of photosynthesis to low-temperature photoinhibition due to interruption of chill-induced increase of S-adenosylmethionine decarboxylase activity in leaves of spinach (Spinacia oleracea L.)

The possible involvement of polyamines in the chilling tolerance of spinach (Spinacia oleracea L.) was investigated focusing on photosynthesis. During chilling at 8/5C (day/night) for 6 d, S-adenosylmethionine decarboxylase (SAMDC) activity increased significantly in leaves in parallel with the increase in putrescine and spermidine (Spd) content in leaves and chloroplasts. Treatment of leaves with methylglyoxal-bis(guanylhydrazone) (MGBG), an SAMDC inhibitor, resulted in the deterioration of plant growth and photosynthesis under chilling conditions, which was reversed by the concomitant treatment with Spd through the roots. Plants treated with MGBG showed lower photochemical efficiency of PSII than either the control or plants treated with MGBG plus Spd during chilling and even after transfer to warm conditions, suggesting an increase of photoinhibition due to low Spd in chloroplasts. Indeed, MGBG-treated plants had much lower activities of thylakoid electron transport and enzymes in carbon metabolism as well as higher degrees of lipid peroxidation of thylakoid membranes compared to the control. These results indicate that the enhanced activity of SAMDC with a consequential rise of Spd in chloroplasts is crucial for the cold acclimation of the photosynthetic apparatus in spinach leaves.     

Antioxidative responses and their relation to salt tolerance in <Emphasis Type="Italic">Echinochloa oryzicola</Emphasis> Vasing and <Emphasis Type="Italic">Setaria virdis</Emphasis> (L.) Beauv.

Two gramineous species among wild plants, Echinochloa oryzicola Vasing and Setaria viridis (L.) Beauv., and Oryza sativa L. cv. Nipponbare were subjected to salt stress. The relative growth rate (RGR), Na content, photosynthetic rate, antioxidant enzymes activity (superoxide disumutase (SOD), catalase (CAT), ascorbate peroxidase (APx) and glutathione reductase (GR)), and malondialdehyde (MDA) content in leaves after NaCl treatment were studied. RGR significantly decreased in O. sativa more than in E. oryzicola and S. viridis. Comparatively salt-tolerant S. viridis showed higher growth rate, lower Na accumulation rate in leaves, higher photosynthetic rate, and induced more SOD, CAT, APx, and GR activity and lower increase of MDA content as compared to the salt-sensitive O. sativa. At the same time, the comparatively salt-tolerant E. oryzicola also showed higher growth rate, much lower Na accumulation and no observable increase of MDA content, even though the CAT and APx activities were not induced by salinity. These results suggested that the scavenging system induced by H₂O₂-mediated oxidative damage might, at least in part, play an important role in the mechanism of salt tolerance against cell toxicity of NaCl in some gramineous plants     

外源水杨酸对NaCl胁迫下白榆幼苗光合作用及离子分配的影响

以1年生白榆幼苗为研究对象,设置0、0.5、1.0和2.0 mmol·L^-1水杨酸(SA)与0、50、100和150 mmol·L^-1 NaCl处理组合,考察盐胁迫下白榆幼苗生物量、光合色素含量、光合作用参数及根叶离子含量、分配、运输的情况,探讨外源SA对NaCl胁迫下白榆幼苗耐盐生理特征的影响。结果表明:(1)NaCl胁迫显著抑制了白榆幼苗的生长、光合色素含量及光合能力,并破坏了白榆体内离子平衡。(2)喷施外源SA使盐胁迫下白榆幼苗的干重和根冠比均不同程度升高,0.5和2.0 mmol·L^-1 SA不同程度提高了50和100 mmol·L^-1 NaCl处理组幼苗叶片光合色素含量。(3)0.5 mmol·L^-1 SA显著提升了50 mmol·L^-1 NaCl处理组白榆幼苗的净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr),1.0和2.0 mmol·L^-1 SA对150 mmol·L^-1 NaCl处理组幼苗净光合速率改善效果较好,外源SA对100 mmol·L^-1 NaCl处理组幼苗的光合作用参数无显著影响。(4)NaCl胁迫下,外源SA处理的白榆幼苗叶和根Na^+含量及Na^+/K^+、Na^+/Ca^2+和Na^+/Mg^2+显著降低,离子选择运输系数SK,Na、SCa,Na和SMg,Na升高,从而促进了幼苗K^+、Ca^2+和Mg^2+由根向叶片的转运;隶属函数分析发现对白榆幼苗叶和根中离子含量改善效果最好的SA浓度分别为1.0和2.0 mmol·L^-1。因此,适宜浓度的外源水杨酸能够有效改善NaCl胁迫下白榆幼苗的光合能力,有效调节白榆幼苗体内离子状态,从而增强白榆对NaCl胁迫的抗性。     

NaCl胁迫对马齿苋光合作用及叶绿素荧光特性的影响

以马齿苋为材料,采用温室盆栽法研究了14 d NaCl胁迫处理对其幼苗生长、光合作用和叶绿素荧光特性的影响.结果显示:(1)马齿苋幼苗的鲜重和株高在25 mmol·L-1 NaCl胁迫时与对照无显著差异,但其随着NaCl浓度的继续增加均显著降低,且其生物量受到的抑制早于株高.(2) NaCl胁迫下,马齿苋幼苗叶片净光合速率(Pn)降低,胞间二氧化碳浓度(C1)增大,且两者的变化幅度随着NaCl浓度增加而增大.(3)NaCl胁迫下,马齿苋幼苗叶片的初始荧光(F0)、最大荧光(Fm)、可变荧光(Fv)、恒态荧光(Fs)、恒态荧光与初始荧光差值(△F0)、PSⅡ潜在光化学效率(Fv/Fo)和PSⅡ最大光化学效率(Fv/Fm)均降低,叶片光化学荧光猝灭系数(qP)也在NaCl胁迫下降低,而非光化学荧光猝灭系数(NPQ)则上升;在0～50 mmol·L-1NaCl胁迫下,幼苗叶片各荧光参数下降幅度小于其他高浓度NaCl胁迫.研究表明,在NaCl胁迫条件下,马齿苋幼苗叶片的光合作用受光抑制伤害,但在低浓度NaCl下能够较多地将光能用于光化学反应,光抑制程度较低,保持了较高的净光合速率,明显减轻盐胁迫对植株生长的影响,表现出一定的耐盐性.     

不同氮浓度和形态比例对水曲柳幼苗叶绿素合成、光合作用以及生物量分配的影响 (英文)

 水曲柳（Fraxinus mandshurica）是我国东北林区重要的工业用材树种,在东北林区广泛种植,因而其培育近来日益得到高度重视。在水曲柳的种植区域内,尽管林地内凋落物丰富,但该地区气温低,冬季长,氮素矿化速度低,氮素供给显得不足。本研究采用沙培的方式,在为幼苗提供完     

Light activation and molecular-mass changes of NAD(P)-glyceraldehyde 3-phosphate dehydrogenase of spinach and maize leaves

Light modulation of chloroplast glyceraldehyde 3-phosphate dehydrogenase (NAD(P)-GAPDH; EC 1.2.1.13) has been investigated. Complete activation of NADPH-dependent activity is achieved at 25 W.m^–2 photosynthetically active radiation in spinach (Spinacia oleracea L.) and 100 W.m^–2 in maize (Zea mays L.) leaves. Light activation is stronger in spinach (fivefold on average) than in maize (twofold), which shows higher dark activity. The NADH dependent activity does not change appreciably. Several substrate activators can simulate in vitro the light effect with recovery of latent NADPH-dependent activity of spinach enzyme, but they are almost inactive with maize enzyme. A mixture of activators has been devised to fully activate the spinach enzyme under most conditions. The NAD(P)-GAPDH protein can be resolved by rapid gel filtration (fast protein liquid chromatography) into three conformers which have different molecular masses according to the light conditions. Enzyme from darkened leaves or chloroplasts, or dichlorophenyl-1,1-dimethylurea-treated chloroplasts is mainly a 600-kDa regulatory form with low NADPH-dependent activity relative to NADH-activity. Enzyme from spinach leaves or chloroplasts during photosynthesis is mainly a 300-kDa oligomer, which along with the 600-kDa form also occurs in leaves of darkened maize. The conformer of illuminated maize leaves is mainly a 160-kDa species. Results are consistent with a model of NAD(P)-GAPDH freely interconvertible between protomers of the 160-kDa (or 300-kDa intermediate) form with high NADPH-activity, produced in the light by the action of thioredoxin and activating metabolites (spinach only), and a regulatory 600-kDa conformer with lower NADPH-activity produced in darkness or when photosynthesis is inhibited. This behavior is reminiscent of the in-vitro properties of purified enzyme; therefore, it seems unlikely that NAD(P)-GAPDH in the chloroplast is part of a stable multienzyme complex or is bound to membranes.Abbreviations AEM activator equilibrium mixture - Chl chlorophyll - DCMU dichlorophenyl 1,1-dimethylurea - DTT dithiothreitol - FPLC fast protein liquid chromatography - NAD(P)-GAPDH glyceraldehyde 3-phosphate dehydrogenase, NAD(P)-dependent - PAR photosynthetic active radiation - PGK phosphoglycerate kinase - Tricine N-tris(hydroxy-methyl) methyl-glycine This work was supported by grants from the Ministero dell'Università e della Ricerca Seientifica e Tecnologica (40%, years 1990 and 1991).     

Effects of salt on growth,ion accumulation,photosynthesis and leaf anatomy of the mangrove,<Emphasis Type="Italic"> Bruguiera parviflora</Emphasis>

The effects of a range of salinity (0, 100, 200 and 400 mM NaCl) on growth, ion accumulation, photosynthesis and anatomical changes of leaves were studied in the mangrove, Bruguiera parviflora of the family Rhizophoraceae under hydroponically cultured conditions. The growth rates measured in terms of plant height, fresh and dry weight and leaf area were maximal in culture treated with 100 mM NaCl and decreased at higher concentrations. A significant increase of Na⁺ content of leaves from 46.01 mmol m^-2 in the absence of NaCl to 140.55 mmol m^-2 in plants treated with 400 mM NaCl was recorded. The corresponding Cl^- contents were 26.92 mmol m^-2 and 97.89 mmol m^-2. There was no significant alteration of the endogenous level of K⁺ and Fe²⁺ in leaves. A drop of Ca²⁺ and Mg²⁺ content of leaves upon salt accumulation suggests increasing membrane stability and decreased chlorophyll content respectively. Total chlorophyll content decreased from 83.44 g cm^-2 in untreated plants to 46.56 g cm^-2 in plants treated with 400 mM NaCl, suggesting that NaCl has a limiting effect on photochemistry that ultimately affects photosynthesis by inhibiting chlorophyll synthesis (ca. 50% loss in chlorophyll). Light-saturated rates of photosynthesis decreased by 22% in plants treated with 400 mM NaCl compared with untreated plants. Both mesophyll and stomatal conductance by CO₂ diffusion decreased linearly in leaves with increasing salt concentration. Stomatal and mesophyll conductance decreased by 49% and 52% respectively after 45 days in 400 mM NaCl compared with conductance in the absence of NaCl. Scanning electron microscope study revealed a decreased stomatal pore area (63%) in plants treated with 400 mM NaCl compared with untreated plants, which might be responsible for decreased stomatal conductance. Epidermal and mesophyll thickness and intercellular spaces decreased significantly in leaves after treatment with 400 mM NaCl compared with untreated leaves. These changes in mesophyll anatomy might have accounted for the decreased mesophyll conductance. We conclude that high salinity reduces photosynthesis in leaves of B. parviflora, primarily by reducing diffusion of CO₂ to the chloroplast, both by stomatal closure and by changes in mesophyll structure, which decreased the conductance to CO₂ within the leaf, as well as by affecting the photochemistry of the leaves.     

盐地碱蓬二型性种子及其幼苗对盐渍环境的适应性

研究了盐地碱蓬二型性种子中离子含量与刚萌发幼苗耐盐性之间的关系,以及盐分对砂培盐地碱蓬二型性种子的幼苗生长、离子含量及光合特性的影响.棕色种子中离子含量显著高于黑色种子.与对照相比,100和400 mmol/L NaCl对棕色种子幼苗伸长没有抑制作用,却显著抑制黑色种子幼苗的伸长.NaCl处理下棕色种子的幼苗地上部分干重和主茎一级分枝数比黑色种子幼苗高,但二型性种子的幼苗叶片中离子含量、叶绿素含量及光合放氧速率却没有明显差异.上述结果说明盐地碱蓬棕色种子较高的离子含量可能是棕色种子刚萌发幼苗耐盐性较强的重要原因.棕色种子幼苗较高的生物量可能与其较多的分枝数有关.二型种子的这些特征可能决定了其在群落建成中所起到的不同作用.     

NaCl 胁迫对盐芥和拟南芥光合作用的影响

本研究检测了与盐芥(Ghellungiella halophila)和拟南芥(Arabidopsis thaliana)光合作用相关的叶绿素、净光合速率(photosynthetic rate, Pn)、气孔导度(stomatal conductance, Gs)、胞间隙CO2浓度以及叶绿素荧光参数等指标, 观察到随着NaCl浓度逐渐增加, 盐芥的叶绿素a/b值(Chl a/Chl b)、类胡萝卜素/总叶绿素值(Car/Chl)显著高于拟南芥, 且二比值变化幅度较小并保持较高水平。盐胁迫下拟南芥净光合速率下降、气孔导度下降和胞间CO2浓度减小。气孔因素是引起拟南芥光合能力下降的主要因素。叶绿素荧光参数的变化表明, 50-200 mmol.L-1 NaCl降低拟南芥叶绿体对光能的吸收能力, 而且降低叶绿体的光化学活性, 使电子传递速率和光能转化效率大幅度下降,造成光能转化为化学能的过程受阻,进一步加剧了光合放氧和碳同化能力的降低。而50-200 mmol.L-1 NaCl 胁迫没有使盐芥的光合作用受到不良影响。     

蓝桉凋落叶分解对菠菜生长及光合特性的影响

通过盆栽试验,模拟蓝桉(Eucalyptus globulus)凋落叶在土壤中分解对受体植物菠菜(Spinacia oleracea)生长及光合特性的影响,设置L30(30 g/盆)、L60(60 g/盆)、L90(90 g/盆)和L120(120 g/盆)4个凋落叶施用水平,对照(CK)不加凋落叶。结果表明:(1)在分解30 d时,低量的凋落叶(L30)未抑制菠菜生物量的积累,而中量和高量处理(L60、L90和L120)下其生物量显著降低(P0.05);在凋落叶分解50 d后,蓝桉凋落叶的化感抑制效应已经减弱,仅L120仍然抑制菠菜生物量的积累;(2)一定量的凋落叶(L30和L60)对菠菜叶绿素的合成有促进作用,而凋落叶超过一定量时(L120)转为抑制作用,在凋落叶分解28 d时相对不明显,40 d后逐渐显现;(3)经凋落叶处理的菠菜叶片胞间CO2浓度(Ci)、气孔导度(Gs)及蒸腾速率(Tr)均显著高于对照(CK)(P0.05),而净光合速率(Pn)在L30处理下最高,L60和L90处理与CK差异不显著,仅L120处理显著低于CK(P0.05);(4)光响应与CO2响应曲线的特征参数表观量子效率(AQY)、最大净光合速率(Pmax)、光饱和点(Lsp)、光补偿点(Lcp)、暗呼吸速率(Rd)、Ru BP表观羧化效率(CE)和光呼吸速率(Rp)在L30处理下高于CK,其余凋落叶处理均低于CK,而CO2饱和点(Csp)、CO2补偿点(Ccp)随凋落叶量的增加而升高。综合各指标可见,少量的蓝桉凋落叶分解(L30)可通过增加叶绿素含量,提高对光和CO2的利用能力促进菠菜的光合作用,进而促进其生长,而凋落叶超过一定量时(L90—L120)则起到相反的作用。     

外源NO和SA对盐胁迫下番茄幼苗叶片膜脂过氧化及AsA-GSH循环的影响

以番茄(Lycopersicon esculentum Mill.)品种‘秦丰保冠’为试材,在水培条件下研究单独和复配施用一氧化氮(NO)供体硝普钠(SNP)、水杨酸(SA)对100 mmol/L NaCl胁迫下番茄幼苗的生长、叶片光合作用、膜脂过氧化及抗坏血酸-谷胱甘肽(AsA-GSH)循环的影响。结果显示,盐胁迫能显著影响番茄幼苗的生长、光合作用和活性氧代谢系统的相关指标。单独或复配施用SNP、SA均能有效缓解番茄幼苗的盐渍伤害,并以SNP和SA复配处理效果最好。处理3~7 d时,叶片PSⅡ最大光化学效率(Fv/Fm)、净光合速率(Pn)、APX、GR、DHAR的活性、AsA和GSH含量分别较胁迫处理有不同程度的提高;而H2O2、MDA、DHA、GSSG的含量和电解质渗漏率分别较胁迫处理有不同程度的降低。研究结果表明盐胁迫下外源NO、SA单独或复配处理均能通过维持或协调作用促进番茄相关抗氧化酶活性的提高和抑制抗氧化剂含量的降低,起到维持AsA-GSH循环高效运转、减轻膜脂过氧化、促进光合作用、改善植株生长发育和提高幼苗盐渍抗性的作用,且NO和SA复配处理时具有协同增效的作用。     

Developing embryos of Sesbania sesban have unique potential to photosynthesize under high osmotic environment

This study has been carried out to investigate the photosynthetic activities in developing embryos of Sesbania sesban under a highly osmotic environment. In S. sesban, the embryo turns green/chlorophyllous at the early heart shape stage. Interestingly, despite being deeply embedded within the supporting tissues (several layers of pod wall, seed coat and endosperm) and developing in a highly osmotic environment, the growing embryo of the developing seed showed the presence of various components of photosynthetic machinery besides being chlorophyllous. The shade-adaptive nature of the photosynthetic machinery of the embryo is evident from (a) low chlorophyll a/b ratio, (b) photosystem (PS) II attaining maximal activity at low photon flux density and (c) lesser plastoquinone pool. The photosynthetic potential of the growing embryo seems to contribute towards seed filling as it has the potential not only to harvest light energy but also to fix CO2 as efficiently as other photosynthetic parts of S. sesban. In fact, ribulose-1,5 bisphosphate carboxylase purified from embryos manifested subunit composition similar to that of leaves. The PS II activity in leaves, cotyledonary leaves and pod wall declined sharply with increase in the level of NaCl and sucrose above 150 and 300 mmol, respectively. Amazingly, PS II activity in developing embryos was maximal in the presence of 250 mmol NaCl or 500 mmol sucrose and remained high even when NaCl and sucrose levels were increased to 500 and 1000 mmol, respectively. We hypothesize that the developing embryos have some factor(s) which protect(s) the photosynthetic machinery in an environment of high osmotic strength.