机械损伤对重瓣玫瑰防御酶的诱导

为研究重瓣玫瑰（Rosa rugosa ‘plena’）的诱导抗虫性,采用机械损伤方式诱导处理重瓣玫瑰,研究机械损伤对重瓣玫瑰叶片防御酶活性的影响。结果表明,机械损伤可诱导重瓣玫瑰叶片苯丙氨酸解氨酶(PAL)、多酚氧化酶(PPO)、过氧化物酶(POD)活性的增加,PPO、POD活性先升高后下降,PAL活性的升高持续时间较长。T3（打孔损伤,3孔/叶）处理为最适的损伤程度,诱导的PAL、PPO、POD活性分别在第7、3、5天达到最高值。因此认为,采用适度地损伤能够诱导重瓣玫瑰较高的防御酶活性,提高植株的防御能力。     

蓟马取食、机械损伤以及外源水杨酸甲酯和茉莉酸对菜豆叶片防御酶活性的影响

【目的】探讨菜豆对昆虫取食防御反应的生化机制。【方法】研究了西花蓟马Frankliniella occidentalis取食、机械损伤以及外源水杨酸甲酯（MeSA）和茉莉酸（JA）处理后菜豆叶片防御酶活性的变化。【结果】西花蓟马取食、机械损伤及MeSA和JA处理均能明显提高过氧化物酶（POD）的活性,前2种处理POD活性在72 h上升到最高峰,而后2种处理则在48 h达到最高峰。蛋白酶抑制剂（PI）活性在西花蓟马取食后升高最明显。JA途径关键酶脂氧合酶（LOX）和多酚氧化酶（PPO）的活性在西花蓟马取食、机械损伤和JA诱导处理均升高,但外源MeSA诱导处理则不能诱导它们的活性(P>0.05)。SA途径的关键酶苯丙氨酸解氨酶（PAL）在西花蓟马取食和机械损伤后均有一个先升高后下降的过程,外源MeSA诱导只在24 h引起PAL活性升高,其余时间下和对照没有明显的区别,外源JA诱导未能引起PAL活性的显著变化(P>0.05)。西花蓟马取食、JA和MeSA诱导以及机械损伤均能诱导β-1,3 葡聚糖酶（PR-2）活性上升(P<0.05)。【结论】结果说明,不同处理可诱导菜豆植株产生明显的防御反应,但酶活性的变化与处理方式和处理时间有关。     

Different responses of young and expanded lettuce leaves to fungicide Mancozeb: chlorophyll fluorescence,lipid peroxidation,pigments and proline content

This work aimed to study the effects of commercial doses of the fungicide, Mancozeb, on the photosynthetic apparatus of lettuce young leaves (YL) and expanded leaves (EL). Seven days after Mancozeb application, chlorophyll a fluorescence, pigment contents, lipid peroxidation, and proline content were evaluated. Independently of leaf age, Mancozeb treatment reduced the efficiency of photosystem II photochemistry, increased the nonphotochemical quenching and proline content, decreased pigment contents, and induced lipid peroxidation. Moreover, EL showed a more stable photosynthetic apparatus, less prone to oxidative damages compared with YL. The parameters measured proved to be good markers for the rapid and preliminary diagnosis of fungicide toxicity.     

高大气CO2浓度下氮素对小麦叶片光能利用的影响

关于氮素对高大气CO₂浓度下C₃植物光合作用适应现象的调节机理已有较为深入的研究, 但对其光合作用适应现象的光合能量转化和分配机制缺乏系统分析。该文以大气CO₂浓度和施氮量为处理手段, 通过测定小麦(Triticum aestivum)抽穗期叶片的光合作用-胞间CO₂浓度响应曲线以及荧光动力学参数来测算光合电子传递速率和分配去向, 研究了长期高大气CO₂浓度下小麦叶片光合电子传递和分配对施氮量的响应。结果表明, 与正常大气CO₂浓度处理相比, 高大气CO₂浓度下小麦叶片较多的激发能以热量的形式耗散, 增施氮素可使更多的激发能向光化学反应方向的分配, 降低光合能量的热耗散速率; 大气CO₂浓度升高后小麦叶片光化学淬灭系数无明显变化, 高氮叶片的非光化学猝灭降低而低氮叶片明显升高, 施氮促进PSII反应中心的开放比例, 降低光能的热耗散; 高大气CO₂浓度下高氮叶片通过PSII反应中心的光合电子传递速率(J_F)较高, 而且参与光呼吸的非环式电子流速率(J₀)显著降低, 较正常大气CO₂浓度处理的高氮叶片下降了88.40%, 光合速率增加46.47%; 高大气CO₂浓度下小麦叶片J_F-J₀升高而J₀/J_F显著下降, 光呼吸耗能被抑制, 更多的光合电子分配至光合还原过程。因此, 大气CO₂浓度增高条件下, 小麦叶片激发能的热耗散速率增加, 但增施氮素后小麦叶片PSII反应中心开放比例提高, 光化学速率增加, 进入PSII反应中心的电子流速率明显升高, 光呼吸作用被抑制, 光合电子较多地进入光化学过程, 这可能是高氮条件下光合作用适应性下调被缓解的一个原因。     

外源硫对镉胁迫下马齿苋光合性状和矿质元素吸收的影响

从光合反应系统揭示外源硫(S)诱导马齿苋镉(Cd)耐受性的生理机制,为外源S缓解重金属毒害提供理论依据.采用营养液培养,研究外源S供体(NH4)2SO4对100 mg/L Cd胁迫下马齿苋叶片光合色素、光合特性、叶绿素荧光参数和矿质营养元素的影响.结果表明,Cd胁迫可显著降低马齿苋叶片中叶绿素a和叶绿素b含量;净光合速率、蒸腾速率、气孔导度均显著降低,而胞间二氧化碳浓度上升,表明非气孔因素是Cd胁迫诱导马齿苋光合抑制的主要因素;同时,PSⅡ实际光化学效率(ФPSII)、电子传递效率(J)、化学猝灭系数(qP)显著下降,而非化学猝灭系数(qN)显著上升,表明Cd胁迫影响马齿苋PSⅡ反应系统的正常运行.外施400 mg/L(NH4)2SO4显著提高马齿苋叶片叶绿素a含量、叶绿素b含量和叶绿素a/b比值,增强马齿苋叶片光合作用和PSⅡ原初光化学反应量子效率.对5种与光反应系统密切相关的矿质元素含量进行分析发现,Cd处理显著增加马齿苋叶片中的Ca和Fe含量,显著抑制马齿苋对Mg、Mn和Cu的吸收.Cd胁迫下马齿苋叶片的变黄与Mg、Mn的亏缺有关,而与Fe缺乏无关;添加外源S可显著提升马齿苋叶片中Ca、Mg、Fe、Cu和Mn含量,从而增强Cd胁迫下马齿苋叶片的PSII反应系统功能.     

重金属对盐生草光合生理生长特性的影响

以盐生草幼苗为试验材料,分别设置0(CK)、50、100、200、400μg?g-1的Ni2+、Cu2+处理,研究重金属Ni2+和Cu2+对盐生草光合生理特性的影响.结果表明:盐生草叶片光合色素含量、净光合速率(Pn)、气孔导度Gs、蒸腾速率Tr、PSⅡ最大光化学效率Fv/Fm、非光化学猝灭系数qN及生长指标(株高、地上部干重和鲜重)在50μg?g-1的Ni2+处理时均达到最大值,后随Ni2+浓度继续增加,其叶片叶绿素a、叶绿素b、Pn、Gs、Tr、Fv/Fm、PSⅡ电子传递量子产率ΦPSⅡ、光化学猝灭系数qP、qN及各项生长指标逐步下降并低于对照水平,而细胞间隙CO2浓度(Ci)较对照呈增加趋势.在50μg?g-1的Cu2+处理时,盐生草叶片光合色素含量、Pn、Gs、Tr、Ci、Fv/Fm、ΦPSⅡ、qP、qN及各项生长指标均达峰值;在100μg?g-1Cu2+处理时,光合色素含量、Pn、Gs、Tr、Fv/Fm、ΦPSⅡ、qN及各项生长指标较对照仍有增加,而后随Cu2+浓度继续增加,其叶绿素a、叶绿素b、各光合参数、叶绿素荧光参数及生长指标均逐步降低并低于对照.可见,盐生草Pn在Ni2+胁迫下的下降主要是由非气孔限制所致,而Cu2+胁迫下的下降主要是由气孔限制所致;低浓度Ni2+和Cu2+对盐生草生长具有一定促进作用,过高浓度Ni2+和Cu2+则会通过抑制盐生草叶片叶绿素合成,影响其光合作用,从而抑制植株生长.     

Antioxidant system and photosynthetic characteristics responses to short-term PEG-induced drought stress in cucumber seedling leaves

The effect of short-term drought stress on the water content, antioxidant system and photosynthetic characteristics was investigated using cucumber (Cucumis sativus L.) seedlings. The results indicated that polyethylene glycol induced water stress reduced water content in shoots of cucumber seedling after treatment of 36 hours, and caused obvious reductions in net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration of leaves. In addition, water stress significantly reduced the photosynthetic pigment content and inhibited photochemical activity, including actual photochemical efficiency, maximal quantum yield of photosystem II photochemistry and coefficient for photochemical quenching. Meanwhile non-photochemical quenching increased. As responses to drought stress, significant increases in electrolyte leakage, malondialdehyde, superoxide anion and hydrogen peroxide levels were detected in leaves. The superoxide dismutases, catalase, glutathione reductase and dehydroascorbate reductase activities, protein, ascorbate and glutathione content, all decreased and peroxidases activity increased, while ascorbate peroxidase and monodehydroascorbate reductase activities exhibited different trend under different degree of water stress. Therefore, it can be concluded that water stress strongly disrupted the normal metabolism of leaves and restrained water absorption.     

Brassinosteroids protect photosynthesis and antioxidant system of eggplant seedlings from high-temperature stress

The effects of 24-epibrassinolide under high temperature in eggplant (Solanum melongena L.) seedlings were studied by investigating the plant growth, chlorophyll content, photosynthesis and antioxidant systems. High temperature significantly inhibited the plant growth and markedly decreased the chlorophyll content, net photosynthetic rate, stomatal conductance and transpiration rate, while it increased intercellular CO₂ concentration. In a similar manner, high temperature also decreased significantly maximum quantum efficiency of PSII, potential photochemical efficiency, the quantum efficiency of PSII, photochemical quenching, the excitation capture efficiency of open centers, and increased non-photochemical quenching. Application of 0.05–0.2 μM EBR remarkably promoted the plant growth and alleviated high-temperature-induced inhibition of photosynthesis. Under high temperature, reactive oxygen species levels and lipid peroxidation were markedly increased, which were remarkably inhibited by application of 0.05–0.2 μM EBR. The activities of antioxidative enzymes such as superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and contents of ascorbic acid and reduced glutathione were significantly increased during high-temperature treatments, and these increases were more pronounced than those of EBR at 0.05–0.2 μM treatment. The EBR treatment also greatly enhanced contents of proline, soluble sugar and protein under high-temperature stress. Taken together, it can be concluded that 0.05–0.2 μM EBR could alleviate the detrimental effects of high temperatures on plant growth by increasing photosynthetic efficiency and enhancing antioxidant enzyme systems. Addition of 0.1 μM EBR had the best ameliorative effect against high temperature, while the addition of 0.4 μM EBR had no significant effects.     

Time-Resolved Analysis of Signals Involved in Systemic Induction of Pin2 Gene Expression

The systemic induction of proteinase inhibitor genes in tomato plants is mediated either by electrical signals, hydraulic signals or chemical messengers. In the present study we analyzed the effects of mechanical wounding, heat treatment and electrical current application on wild-type tomato plants (Lycopersicon esculentum Mill, cv Moneymaker) and ABA-deficient mutants of tomato (sitiens). Kinetic studies revealed that systemic Pin2 gene expression could be slightly induced by the fast transient membrane potential change which left the damaged leaf within 30–60s after wounding. Moreover, a signal leaving the damaged tissue between 2 and 4 minutes after wounding was responsible for a significant amplification of Pin2 gene expression. This signal could either be a decrease in turgor pressure, which occurred 3–4min after treatment, or a slow electrical transient. In addition, mechanical wounding and electrical current seem to involve ABA to induce changes in membrane potential and to promote Pin2 gene expression. In contrast, heat triggers fast and slow electrical transients leading to an induction of Pin2 gene expression within the plant independently of ABA. Turgor pressure, in turn, is presumably adjusted in relation to ionic movements across the membrane, elucidated by membrane potential recordings. In conclusion, wound-induced changes in membrane potential seem to be dependent on the endogenous level of ABA. These shifts in membrane potentials, in turn, are involved in regulation of turgor pressure within the plant.     

Localized Wounding by Heat Initiates the Accumulation of Proteinase Inhibitor II in Abscisic Acid-Deficient Plants by Triggering Jasmonic Acid Biosynthesis

To test whether the response to electrical current and heat treatment is due to the same signaling pathway that mediates mechanical wounding, we analyzed the effect of electric-current application and localized burning on proteinase inhibitor II (Pin2) gene expression in both wild-type and abscisic acid (ABA)-deficient tomato (Lycopersicon esculentum Mill.) and potato (Solanum phureja) plants. Electric-current application and localized burning led to the accumulation of Pin2 mRNA in potato and tomato wild-type plants. Among the treatments tested, only localized burning of the leaves led to an accumulation of Pin2 mRNA in the ABA-deficient plants. Electric-current application, like mechanical injury, was able to initiate ABA and jasmonic acid (JA) accumulation in wild-type but not in ABA-deficient plants. In contrast, heat treatment led to an accumulation of JA in both wild-type and ABA-deficient plants. Inhibition of JA biosynthesis by aspirin blocked the heat-induced Pin2 gene expression in tomato wild-type leaves. These results suggest that electric current, similar to mechanical wounding, requires the presence of ABA to induce Pin2 gene expression. Conversely, burning of the leaves activates Pin2 gene expression by directly triggering the biosynthesis of JA by an alternative pathway that is independent of endogenous ABA levels.     

外源6-BA对低温胁迫下茄子幼苗光合作用、叶绿素荧光参数及光能分配的影响

本文研究了外源6-BA对低温胁迫下茄子幼苗光合作用、叶绿素荧光参数和能量分配的影响。结果表明,外源6．BA显著增加了低温胁迫下茄子叶绿素含量、净光合速率（Pn）、蒸腾速率（t）、气孔导度（Gs）和胞间CO2浓度（c1）;同时外源6-BA明显提高了低温胁迫下茄子幼苗叶片的PSⅡ最大光化学效率（Fv/Fm）、PSⅡ潜在活性（R／Fo）、PSII天线转化效率（FvFm）、实际光化学效率（φpsⅡ）、光化学猝灭系数（g,）和光化学反应能量（P）,降低了非光化学猝灭系数（NPQ）、天线热耗散能量（D）,对非光化学反应耗散能量（E）无明显影响。表明外源6-BA处理通过促进低温胁迫下茄子幼苗光合作用,提高光合电子传递效率,从而保护光合系统,降低低温胁迫对植物的损伤。     

Early photosynthetic response of Arabidopsis thaliana to temperature and salt stress conditions

Temperature changes and salt accumulation are among the most common abiotic factors affecting plants in agricultural and natural ecosystems. The different responses of plants to these factors have been widely investigated in previous works. However, detailed mechanism of the early photosynthetic response (first 24 h) has been poorly studied. The aim of the work was to monitor the early response of adult Arabidopsis thaliana plants exposed to different thermal (cold and heat) and salt conditions. Detailed evaluation of the efficiency of photosystem II was done, and the various routes of energy output as well as measurements of the contents of H₂O₂, proline, and photosynthetic pigments at different times during the first 24 h of treatment were examined. The conditions used in the study were those that caused a weak stress with time of exposure. Cold-treated plants showed the most continuous inhibitory effect on photosynthetic activity, with a fast metabolic slowdown (reduced PSII efficiency and decreased pigment contents), although they also demonstrated clear acclimation responses (increased heat dissipation and protein content). Heat-treated plants showed a late but stronger effect on photosynthesis with significantly increased quantum yield of nonregulated energy dissipation (??_NO) and H₂O₂ content at the last measurements. Finally, salt-induced oxidative stress (increased H₂O₂ content), decreased PSII efficiency and pigment content.     

苯嗪草酮对苹果坐果和光合生物学特征的影响

为解决苹果人工疏果费时费工、效率低等问题,以矮化中间砧红富士苹果为试材,以清水为对照(CK),研究了幼果期喷施化学疏果剂苯嗪草酮200、300和400 mg ? L-1的疏果效应及对叶片光合生物学特征的影响.结果表明:与CK相比,喷施苯嗪草酮可显著降低花序和花朵坐果率,降幅分别为16.5％～22.8％和50.9％～53...     

Effects of gamma-aminobutyric acid on the photosynthesis and chlorophyll fluorescence parameters of muskmelon seedlings under hypoxia stress

By the method of hydroponic culture, this paper studied the effects of exogenous gamma-aminobutyric acid (GABA) on the photosynthetic pigment contents, photosynthesis, and chlorophyll fluorescence parameters of muskmelon seedlings under hypoxia stress. Hypoxia stress induced a significant decrease of photosynthetic pigment contents, resulting in the decrease of photosynthesis. Applying GABA could significantly increase the photosynthetic pigment contents, net photosynthetic rate (P(n)), stomatal conductance (G(s)), intercellular CO2 concentration (C(i)), carboxylation efficiency (CE), maximal photochemical efficiency of PS II (F(v)/F(m)), photochemical quenching (q(P)), apparent photosynthetic electron transfer rate (ETR), and quantum yield of PS II electron transport (phi(PS II)), and decrease the stomatal limitation value (L(s)), minimal fluorescence (F(o)), and non-photochemical quenching (NPQ) under both hypoxic and normal conditions. The alleviation effect of GABA on photosynthetic characteristics was more obvious under hypoxia stress. However, simultaneously applying GABA and VGB could significantly decrease the alleviation effect of GABA under hypoxia stress.     

诱导处理小麦对蚜虫生长发育的影响及小麦特异基因的表达

分析了麦二叉蚜在小麦98-10-30上不同诱导处理后发育时间、成虫重量和平均相对生长率,以及不同诱导处理下小麦98-10-30特异基因的表达.结果表明,用针刺、蚜虫取食和BTH（benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester）处理98-10-30后,蚜虫发育成成虫的时间缩短,成虫体重下降,平均相对生长率在各处理间无显著差异.对处理后小麦体内特异基因的表达研究表明,LOX、AOS、PDF1.2、PAL1、PR-1和BGL2基因在mRNA的表达量或质上存在差异.PDF1.2基因在蚜虫取食后mRNA的量显著增加,但BTH处理却不诱导PDF1.2基因的表达,同时,BGL2基因在蚜虫取食和BTH处理后,mRNA的量增加,但对照和针刺处理后BGL2基因不表达.不同诱导处理表明,98-10-30诱导的抗性对麦二叉蚜的生长发育有一定影响,蚜虫取食诱导的防卫反应与机械损伤和BTH处理有相似或相同之处,但存在明显差异.这说明蚜虫诱导的抗性是一种特异反应,与受伤反应和抗病反应有重叠交叉之处,但又不同于二者诱导产生的抗性反应.     

机械损伤对Bt玉米化学防御的系统诱导效应

植物在生长过程中形成了抵御机械损伤等外界胁迫的直接和间接防御体系, 并具有明显的系统性特征。Bt (Bacillus thuringiensis)玉米(Zea mays)是全球商品化最快的抗虫转基因作物之一。机械损伤等外界胁迫对Bt玉米和常规玉米化学防御的系统诱导效应是否存在差异是值得探讨的问题。该文以两个不同转化事件的Bt玉米‘5422Bt1’(Bt11)和‘5422CBCL’(Mon810)以及它们共同的同源常规玉米‘5422’幼苗为材料, 对玉米第一叶进行机械损伤处理6 h后, 检测非损伤部位(第二叶和根系)中Bt蛋白含量、直接防御物质丁布(DIMBDA)含量及其调控基因(Bx1、Bx6和Bx9)表达、直接防御物质总酚含量及其调控基因(PAL)表达、直接防御蛋白调控基因(MPI和PR-2a)表达以及间接防御物质挥发物调控基因(FPS和TPS)表达的变化。结果表明, 与健康植株相比, 机械损伤对两个Bt玉米第二叶和根系的Bt蛋白含量均没有显著影响; 机械损伤第一叶只能系统诱导常规玉米‘5422’第二叶中PAL、TPS和根系中PAL、FPS基因的表达, 使得第二叶丁布含量显著增加, 但根中丁布含量及其调控基因Bx6和Bx9基因的表达量明显下降; 而机械损伤能系统诱导Bt玉米‘5422Bt1’第二叶中Bx6、PAL、PR-2a、TPS和根系中Bx6、Bx9、PAL、MPI、PR-2a、TPS基因的表达, 使得第二叶丁布含量明显增加; 对于另一Bt玉米‘5422CBCL’而言, 机械损伤能系统诱导第二叶中Bx9、PAL、PR-2a、TPS和根系中Bx6、PAL、MPI、TPS基因的表达, 使得根系的总酚含量显著增加。由此可见, 机械损伤对两个Bt玉米化学防御反应的系统诱导作用均强于常规玉米‘5422’, 说明在机械损伤的系统诱导防御过程中, 人工导入抗性(Bt基因)与自身化学防御过程之间的互作关系是协同的。     

γ-氨基丁酸（GABA）对低氧胁迫下甜瓜幼苗光合作用和叶绿素荧光参数的影响

采用营养液水培方法,研究了低氧胁迫下外源γ-氨基丁酸（GABA）对甜瓜幼苗光合色素含量、光合作用及叶绿素荧光参数的影响.结果表明：低氧胁迫导致甜瓜幼苗光合色素含量显著下降,光合作用降低;外源GABA能显著提高正常通气和低氧胁迫下甜瓜幼苗的光合色素含量、净光合速率、气孔导度、胞间CO₂浓度、CO₂羧化效率、最大光化学效率、光化学猝灭系数、表观光合电子传递速率和PSⅡ光合电子传递量子效率,而气孔限制值、初始荧光和非光化学猝灭系数显著降低,GABA在低氧胁迫下的提高效果更明显;同时添加GABA和GABA转氨酶抑制剂γ-乙烯基-γ-氨基丁酸（VGB）处理显著降低了低氧胁迫下GABA对甜瓜幼苗光合特性的缓解效果.     

Nicotine concentration in leaves of flue-cured tobacco plants as affected by removal of the shoot apex and lateral buds

It is believed that the nicotine concentration in tobacco is closely correlated with the amount of nitrogen (N) supplied.On the other hand,N uptake mainly occurs at the early growth stage,whereas nicotine concentration increases at the late growth stage,especially after removing the shoot apex.To identify the causes of the increased nicotine concentration in tobacco plants,and to compare the effects of different ways of mechanical wounding on nicotine concentration,field experiments were carried out in Fuzhou,Fujian Province in 2003 and 2004.Excision of the shoot apex had almost no influence on N content in the plant;however,it caused dramatic increases in nicotine concentration in leaves,especially in the middle and upper leaves.An additional increase of the nicotine concentration was obtained by removal of axillary buds.The wounding caused by routine leaf harvests,however,did not change the leaf nicotine concentration,and neither did reducing leaf harvest times.The present results revealed no direct relationship between N supply and nicotine concentration in tobacco leaves,and indicate that not all kinds of mechanical wounding were capable of stimulating nicotine synthesis in tobacco plants.Since nicotine production is highly dependent on the removal of apical meristems and hence on the major sources of auxin in the plant,and application of 1-naphthylacetic acid onto the cut surface of the stem after removing the shoot apex markedly decreased the nicotine concentration in different leaves and the total nicotine content in the plant,the results suggest that decreased auxin supply caused by removal of the shoot apex as a kind of mechanical wounding might regulate nicotine synthesis in the roots of tobacco plants.     

Photosynthesis is improved by exogenous glycinebetaine in salt-stressed maize plants

The effects of exogenous application of glycinebetaine (GB) (10 m M ) on growth, leaf water content, water use efficiency, photosynthetic gas exchange, and photosystem II photochemistry were investigated in maize plants subjected to salt stress (50 and 100 m M NaCl). Salt stress resulted in the decrease in growth and leaf relative water content as well as net photosynthesis and the apparent quantum yield of photosynthesis. Stomatal conductance, evaporation rate, and water use efficiency were decreased in salt-stressed plants. Salt stress also caused a decrease in the actual efficiency of PSII ( Φ _PSII), the efficiency of excitation energy capture by open PSII reaction centers ( F _v'/ F _m'), and the coefficients of photochemical quenching ( q _P) but caused an increase in non-photochemical quenching (NPQ). Salt stress showed no effects on the maximal efficiency of PSII photochemistry ( F _v/ F _m). On the other hand, in salt-stressed plants, GB application improved growth, leaf water content, net photosynthesis, and the apparent quantum yield of photosynthesis. GB application also increased stomatal conductance, leaf evaporation rate, and water use efficiency. In addition, GB application increased Φ _PSII, F _v'/ F _m', and q _P but decreased NPQ. However, GB application showed no effects on F _v/ F _m. These results suggest that photosynthesis was improved by GB application in salt-stressed plants and such an improvement was associated with an improvement in stomatal conductance and the actual PSII efficiency.     

The effects of phenolic acids on the photosynthetic characteristics and growth of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">euramericana</Emphasis> cv. ‘Neva’ seedlings

Populus × euramericana cv. ‘Neva’ is an important tree species in northern China. In the study, we used its potted oneyear- old seedlings as experimental material and established three treatments (CK, 0.5X, and 1.0X) according to the concentrations of phenolic acids in order to examine the effects of different concentrations on the photosynthetic characteristics and growth of poplar. With increasing concentrations of phenolic acids, the net photosynthetic rate, stomatal limitation, transpiration rate, apparent quantum yield, photochemical quenching coefficient, electron transport rate, chlorophyll content, and total biomass decreased significantly. The intercellular CO₂ concentration, light-compensation point, nonphotochemical quenching, malondialdehyde content, and root/shoot ratio increased significantly. Peroxidase and superoxide dismutase activities initially decreased and then increased. We concluded that phenolic acids significantly inhibited poplar’s photosynthesis and the higher phenolic acid concentration, the greater inhibition of photosynthesis occurred. This inhibition effect was mainly caused by nonstomatal factors. Phenolic acids induced noticeable photoinhibition, resulted in the irreversible damage of membrane structure, and then changed intracellular metabolic processes. To cope with phenolic acid stress, poplar seedlings increased dissipation of excess light energy and distributed relatively more biomass to underground parts within carbon allocation.