田间条件下棉花幼叶光合特性及光保护机制

通过比较棉花(Gossypium hirsutum)幼叶和完全展开叶气体交换参数及叶绿素荧光特性的差异, 探讨高光强下幼叶的光抑制程度及明确光保护机制间的协调机理。在田间自然条件下, 以棉花刚展平的幼嫩叶片(幼叶)和面积已达到最大的完全展开叶片为研究对象, 通过测定不同发育阶段叶片气体交换参数及叶绿素a荧光参数的变化, 并运用Dual-PAM100对不同发育阶段的叶片进行快速光响应曲线的拟合。结果表明: 幼叶和完全展开叶片在光合、荧光特性方面表现出明显的差异。与完全展开叶相比, 较低的叶绿素(Chl)含量和气孔导度(G_s)是幼叶较低净光合速率(P_n)的限制因素, 从而直接导致其光系统II (PSII)实际光化学效率(Φ_PSII)和光化学猝灭系数(q_P)的降低。在1800 μmol·m^-2·s^-1光强以下, 完全展开叶具有较强的围绕PSI循环的电子流(CEF), 有利于合成ATP, 是其具有较高光合能力的原因之一。相同光强下, 幼叶较低的光饱和点(LSP)更易受光抑制, 但其PSII原初光化学效率(F_v/F_m)的日变化幅度显著小于完全展开叶, 说明强光下幼叶通过类胡萝卜素(Car)猝灭单线态氧、光呼吸(P_r)、热耗散(NPQ)以及PSI-CEF等光保护机制能有效地耗散过剩的光能, 从而避免其光合机构发生光抑制。     

田间大豆叶片成长过程中的光合特性及光破坏防御机制

田间大豆叶片在成长进程中光饱和光合速率持续提高,但气孔导度的增加明显滞后.尽管叶片在成长初期就具有较高的最大光化学效率,但是仍略低于发育成熟的叶片.随着叶片的成长,光下叶片光系统Ⅱ实际效率增加;非光化学猝灭下降.幼叶叶黄素总量与叶绿素之比较高,随着叶面积的增加该比值下降,在光下,幼叶的脱环氧化程度较高.因此认为大豆叶片成长初期就能够有效地进行光化学调节;在叶片生长过程中依赖叶黄素循环的热耗散机制迅速建立起来有效抵御强光的破坏.     

遮荫和全光下生长的棉花光合作用和叶绿素荧光特征

 遮荫条件下（遮荫下光强相当于自然光强的40％左右）棉花(Gossypium hirsutum)叶片光合速率明显降低,仅为自然光强下生长叶片的30%～40％,叶片中RuBP羧化酶活性降低,而表观量子效率(AQY)较高。不同光照条件下生长的棉花叶片对短时间持续光强的光合诱导过程有明显的差异,由弱光转到强光下,自然光强下生长的叶片的Pn、Gs、ΦPSⅡ及非光化学猝灭系数(NPQ)都能在较短的时间内达到最大值,而遮荫叶片需要的时间较长;遮荫下生长的棉花叶片的实际光化学效率,随光强的增加下降幅度较大,而自然光照下生长的叶片下降幅度较小;自然光照下生长的叶片的NPQ随光强的升高达到较高水平,而遮荫叶片在较低的光强下即达到最大值,此时NPQ较低,遮荫叶片依赖于叶黄素循环的能量耗散水平较低。遮荫叶片较低的光合速率以及过剩光能耗散能力是其转入自然强光后光抑制严重的主要原因。     

热带雨林冠层树种绒毛番龙眼两种发育阶段叶片的光抑制

 通过测定西双版纳热带雨林冠层树种绒毛番龙眼(Pometia tomentosa)完全伸展嫩叶和成熟叶的叶片解剖、生理特征和雨季晴天自然条件下叶绿素a荧光以及午间强光对部分保护酶活性和膜脂过氧化作用的影响,探讨了两种不同发育阶段叶片光合作用的光抑制与强光和温度的关系。结果表明：绒毛番龙眼全展嫩叶和成熟叶表现出明显的解剖和生理特征差异。与全展嫩叶相比,成熟叶的叶片较厚、叶绿素含量高、气孔导度大、羧化效率高、最大净光合速率和光饱和点高,而气孔密度和保卫细胞长度没有显著差别。在雨季晴天自然条件下,午间最高光强可达2 200 μmol·m-2·s-1以上,最高叶温比气温高7～8 ℃,而成熟叶片的最高温度比全展嫩叶高1.5～2 ℃。上午随光强的增大,两种叶片的非光化学猝灭系数（NPQ）增大,PSⅡ原初光化学效率(Fv/Fm)、实际光化学效率［(Fm′_Fs)/Fm′］逐渐减小,在15∶30左右达最小。下午随着光强的减弱,Fv/Fm逐渐恢复,在傍晚基本恢复到清晨值。初始荧光(F0)在一天中变化很小。这表明绒毛番龙眼叶片光抑制是非辐射能量耗散增加引起的保护光合机构免受光破坏的保护性反应,而非光破坏。全展嫩叶比成熟叶有较低的光化学效率和非辐射耗散能力,对强光和高温处理的敏感性也较强,但在自然条件下一天中的光抑制程度与成熟叶没有显著差别。田间午间强光导致两种叶片的保护酶活性(超氧化物歧化酶,SOD;抗坏血酸过氧化物酶,APX)升高,而H2O2含量变化较小。其中,全展嫩叶的保护酶活性高,丙二醛(MDA)含量低。这表明自然条件下,与成熟叶相比,绒毛番龙眼全展嫩叶通过较低的光能利用效率、较低的叶温和高的保护酶活性减轻了强光高温的光抑制程度。     

砂仁叶片光破坏的防御

报告了生长于热带林窗向阳处砂仁叶片叶绿素荧光参数的日变化,及阻止卷叶和用二硫苏糖醇(DTT)处理对它的影响.受强光照射,砂仁叶片迅速卷起.在雾天上午光强还相当弱(低于100μmol m-2s-1)时,砂仁叶片就发生光抑制,中午最重,下午当光强减弱时,光抑制逐渐得到缓解.其热耗散(qN、NPQ)随光强的升高而增加,且下午仍在缓慢增加.阻止卷叶使强光下砂仁叶片光抑制加剧,F0、NPQ升高.DTT处理也使光抑制加剧,F0升高,且使PSⅡ反应中心发生可逆失活.夜间2300各处理的荧光参数基本恢复.卷叶、叶黄素循环和PSⅡ可逆失活3种保护机制在同种植物中依次启动的现象尚属少见.     

干旱胁迫对不同光环境下的三叶漆幼苗光合特性和叶绿素荧光参数的影响

以2年生三叶漆(T erm inth ia p an icu la ta)幼苗为实验材料,研究了生长于全自然光和遮荫条件(光强相当于自然光强的50%)下幼苗的光合特性和叶绿素荧光参数对不同土壤水分条件的响应,探讨了其对干旱和强光胁迫的生理适应机制.结果表明,叶片相对含水量(RW C)、叶水势(Ψ)、最大光合速率(Pm ax)、表观量子效率(AQY)、暗呼吸速率(Rd)和光合色素含量都随干旱胁迫的加剧而下降.Pm ax、AQY、Rd和比叶重(LM A)随光强的增加而升高,色素含量则随光强升高而降低.Ch la/b、C ar/Ch l随干旱程度和光强的增加有升高的趋势.PSⅡ的最大光能转换效率(Fv/Fm)和光化学量子效率(ФPSⅡ)在日间光较强时明显降低,说明发生了光抑制.电子传递速率(ETR)和非光化学猝灭系数(N PQ)随日间光强的增大而升高,表明三叶漆可能通过增强光呼吸和热耗散抵御光抑制、保护光合机构.二元方差分析表明,水分和光强具有明显的交互作用.全自然光下严重干旱的幼苗仍有较高的Pm ax(9.65μm o l.m-2.-s 1),说明三叶漆对干旱和强光具有极强的适应能力,这也是其成为干热河谷植被优势种的重要原因.     

喜光榕树和耐荫榕树光适应机制的差异

100%和36%光强下生长的喜光的斜叶榕的光合能力高于耐荫的假斜叶榕,而热耗散能力与之相似,说明强光下斜叶榕主要通过光合作用利用光能和热耗散、假斜叶榕主要通过热耗散防御光破坏.100%光强下生长的两种榕树的日间光抑制程度相似,但叶表光强相同情况下各光强下生长的假斜叶榕的光抑制均比斜叶榕严重.100%光强下假斜叶榕叶片悬挂角大于斜叶榕,导致日间叶表光强低于斜叶榕,这可能是两种榕树日间光抑制程度相似的原因,表明叶片悬挂角的适应变化对假斜叶榕有重要的意义.     

叶黄素循环和D1蛋白周转在毛竹叶片光保护中的作用

利用叶绿素荧光技术,对强光胁迫下以及叶黄素循环抑制剂-二硫苏糖醇(DTT)和D1蛋白合成抑制剂-硫酸链霉素(SM)处理后毛竹(Phyllostachys edulis (Carr.) Lehaie)的光抑制特征进行研究。结果显示:在夏季中午强光或人为强光胁迫下,毛竹叶片最大光化学效率Fv/Fm均显著降低;在下午光强减弱或黑暗、弱光条件下,Fv/Fm可有效恢复。DTT和SM均可抑制毛竹叶片非光化学淬灭(NPQ),且DTT效果明显优于SM。另外,在强光下,DTT和SM处理均能使毛竹叶片Fv/Fm、实际光化学效率Y(Ⅱ)和光化学淬灭qP等荧光参数下降幅度增大。研究结果表明毛竹叶片具有完善的光破坏防御机制,NPQ与叶黄素循环和D1蛋白周转紧密关联,在叶片光保护机制中具有重要作用。     

紫茎泽兰光合特性对生长环境光强的适应

测定了不同光强下生长的紫茎泽兰叶片最大净光合速率(Pmax)、叶绿素荧光参数、光合色素含量和比叶重(SLW),探讨了其光适应能力及生理生态学机制．强光下(100％相对光强)紫茎泽兰发生了轻度光抑制,Pmax、SLW、类胡萝卜素含量和日间热耗散升高,但热耗散能力没有提高．强光下紫茎泽兰通过：1)加强日间热耗散和活性氧清除能力以及光系统Ⅱ反应中心可逆失活来耗散过剩光能;2)增大P～以增加光能利用;3)提高SLW,降低单位干重叶绿素含量以减少光能吸收3个途径避免了光合机构光破坏．弱光下(36％、12．5％和4．5％相对光强)紫茎泽兰日间热耗散很小,SLW降低,但P～较高,这有利于其增加光能吸收和利用效率．紫茎泽兰能在很大的光强范围内有效地维持光合系统正常运转,这可能是其表现较强入侵性的原因之一．     

4种木本植物叶片的光合电子传递和吸收光能分配特性对光强的适应

以气体交换和叶绿素荧光测定相结合的方法研究了亚热带自然林乔木荷树、黧蒴和林下灌木九节、罗伞幼苗的光合电子传递及激发能利用的分配对生长光强的适应特性。4种植物生长于100%、36%和16%的自然光下8个月,叶片的光化学速率和热能耗散速率随光强增大而提高,热能耗散占总的光能吸收的比例也因光强不同而改变,16%光下的相对热耗散率约为40%～45%,100%自然光下增大至50%～75%。叶片总的非环式电子流速率及其分配到光呼吸的比例在100%光强下最高。乔木和灌木的电子传递和光能分配特性在16%光下相似,在100%光下差别较明显。除灌木种有较高的热耗散比例之外,其余的参数皆比乔木的低。结果表明乔木与灌木皆可通过提高激发能热耗散比例和提高光合电子传递向光呼吸的比例来适应于高光强条件。     

Enhanced antioxidant protection at the early stages of leaf expansion in ginkgo under natural environmental conditions

Photosynthetic pigments, gas exchange, chlorophyll (Chl) a fluorescence kinetics, antioxidant enzymes and chloroplast ultrastructure were investigated in ginkgo (Ginkgo biloba L.) leaves from emergence to full size. Under natural conditions, the net photosynthetic rate (P_N), contents of Chl a, Chl b and total soluble proteins and fresh and dry leaf mass gradually increased during leaf expansion. The maximum photochemical efficiency of photosystem (PS) 2 (variable to maximum fluorescence ratio, F_v/F_m) was considerably higher at the early stages of leaf development than in fully expanded leaves. During daily course, only reversible decrease in F_v/F_m was distinguished at various stages, implying that no photo-damage occurred. Absorption flux per cross section (CS) and trapped energy flux per CS were significantly lower in newly expanding leaves compared with fully expanded ones, however, dissipated energy flux per CS was only slightly lower in expanding leaves. The ratio of carotenoids (Car)/Chl decreased gradually during leaf expansion due to increasing Chl content. Moreover, activities of the antioxidant enzymes, such as superoxide dismutase, ascorbate peroxidase, catalase and peroxidase, increased at the early stages of leaf expansion. The appearance of osmiophilic granules in fully expanded leaves further proves that photo-protection is significantly strengthened at the early stages of leaf expansion.     

Variations in light energy dissipation in <Emphasis Type="Italic">Woodfordia fruticosa</Emphasis> leaves during expansion

Young leaves of tropical trees frequently appear red in color, with the redness disappearing as the leaves mature. During leaf expansion, plants may employ photoprotective mechanisms to cope with high light intensities; however, the variations in anthocyanin contents, nonphotochemical quenching (NPQ), and photorespiration during leaf expansion are poorly understood. Here, we investigated pigment contents, gas exchange, and chlorophyll (Chl) fluorescence in Woodfordia fruticosa leaves during their expansion. Young red leaves had significantly lower Chl content than that of expanding or mature leaves, but they accumulated significantly higher anthocyanins and dissipated more excited light energy through NPQ. As the leaves matured, net photosynthetic rate, total electron flow through PSII, and electron flow for ribulose-1,5-bisphosphate oxygenation gradually increased. Our results provided evidence that photorespiration is of fundamental importance in regulating the photosynthetic electron flow and CO₂ assimilation during leaf expansion.     

A novel method for the estimation of soybean chlorophyll content using a smartphone and image analysis

The development of smartphones, specifically their cameras, and imaging technologies has enabled their use as sensors/measurement tools. Here we aimed to evaluate the applicability of a fast and noninvasive method for the estimation of total chlorophyll (Chl), Chl a, Chl b, and carotenoids (Car) content of soybean plants using a smartphone camera. Single leaf disc images were obtained using a smartphone camera. Subsequently, for the same leaf discs, a Chl meter was used to obtain the relative index of Chl and the photosynthetic pigments were then determined using a classic method. The RGB, HSB and CIELab color models were extracted from the smartphone images and correlated to Chl values obtained using a Chl meter and by a standard laboratory protocol. The smartphone camera was sensitive enough to capture successfully a broad range of Chl and Car contents seen in soybean leaves. Although there was a variation between color models, some of the proposed regressions (e.g., the S and b index from HSB and Lab color models and NRI [RGB model]) were very close to the Chl meter values. Based on our findings, smartphones can be used for rapid and accurate estimation of soybean and Car contents in soybean leaves.     

O3浓度升高和UV-B辐射增强对大豆叶片叶绿素含量和活性氧代谢的影响

以大豆栽培品种铁丰29为试验材料,利用开顶式气室研究O₃浓度升高和UV B辐射增强复合胁迫对大豆叶片叶绿素(Chl)含量、膜脂过氧化程度、活性氧产生速率、抗氧化酶活性和籽粒产量的影响.结果表明： 在大豆整个生育期内,与对照相比,O₃和UV-B单一胁迫及其复合胁迫下的大豆叶片Chl(a+b)、Chl a和Chl b含量均呈下降趋势;相对电导率、丙二醛含量增大,活性氧产生速率和H₂O₂含量增加,超氧化物歧化酶、过氧化物酶和过氧化氢酶活性下降,产量降低.O₃和UV-B复合胁迫加剧了大豆叶片膜脂过氧化程度,促进大豆体内活性氧自由基的产生,使大豆抗氧化能力减弱,叶绿素含量降低,对大豆表现为协同效应.O₃胁迫对大豆叶片的影响与复合胁迫更相近,其原因可能是在复合胁迫中臭氧起主要作用.     

Spectral reflectance indices and pigment functions during leaf ontogenesis in six subtropical landscape plants

Pigment combinations are regulated during leaf ontogenesis. To better understand pigment function, alterations in chlorophyll, carotenoid and anthocyanin concentrations were investigated during different leaf development stages in six subtropical landscape plants, namely Ixora chinensis Lam, Camellia japonica Linn, Eugenia oleina Wight, Mangifera indica L., Osmanthus fragrans Lowr and Saraca dives Pierre. High concentrations of anthocyanin were associated with reduced chlorophyll in juvenile leaves. As leaves developed, the photosynthetic pigments (chlorophyll and carotenoid) of all six species increased while anthocyanin concentration declined. Chlorophyll fluorescence imaging of Φ_PSII (effective quantum yield of PSII) and of NPQ (non-photochemical fluorescence quenching) and determination of electron transport rate-rapid light curve (RLC) showed that maximum ETR (leaf electron transport rate), Φ_PSII and the saturation point in RLC increased during leaf development but declined as they aged. Juvenile leaves displayed higher values of NPQ and Car/Chl ratios than leaves at other developmental stages. Leaf reflectance spectra (400–800 nm) were measured to provide an in vivo non-destructive assessment of pigments in leaves during ontogenesis. Four reflectance indices, related to pigment characters, were compared with data obtained quantitatively from biochemical analysis. The results showed that the ARI (anthocyanin reflectance index) was linearly correlated to anthocyanin concentration in juvenile leaves, while a positive correlation of Chl NDI (chlorophyll normalized difference vegetation index) to chlorophyll a concentration was species dependent. Photosynthetic reflectance index was not closely related to Car/Chl ratio, while a structural-independent pigment index was not greatly altered by leaf development or species. Accordingly, it is suggested that the high concentration of anthocyanin, higher NPQ and Car/Chl ratio in juvenile leaves are important functional responses to cope with high radiation when the photosynthetic apparatus is not fully developed. Another two leaf reflectance indices, ARI and Chl NDI, are valuable for in vivo pigment evaluation during leaf development.     

Effects of 6N-Benzyladenine on Primary Leaves of Intact Bean Plants and on their Sodium Absorption Capacity

The application of ⁶N-benzyladenine (BA) to primary bean-leaves attached to the intact plant resulted in increased leaf area. This was due to an extension of the duration of the period of leaf expansion. The dry-weight percentage of untreated leaves decreased continuously from emergence to abscission. In BA treated leaves this decrease stopped with the cessation of leaf expansion. Net chlorophyll synthesis occurs in untreated leaves as long as they continue to expand, shortly afterwards net chlorophyll decomposition starts. Benzyladenine treatments diminished the rate of chlorophyll synthesis immediately after its first application, but prevented the loss of chlorophyll afterwards. The abscission of primary leaves was also delayed by BA. During the period of rapid leaf expansion in slices cut from BA treated leaves, sodium absorption rates were lower than in those from untreated leaves. From the age of 14 days after sowing, till abscission time of untreated primary leaves, the BA treatment did not significantly affect sodium absorption rates by leaf slices.     

Photosynthetic characterization of Jerusalem artichoke during leaf expansion

Gas exchange, chlorophyll a fluorescence and modulated 820 nm reflection were investigated to explore the development of photosynthesis in Jerusalem artichoke (Helianthus tuberosus L.) leaves from initiation to full expansion. During leaf expansion, photosynthetic rate (Pn) increased and reached the maximal level when leaves were fully expanded. The same change pattern was also found in the stomatal conductance and chlorophyll content. Lower Pn could not be ascribed to the higher stomatal resistance in developing leaves, as intercellular CO₂ concentration was not significantly lower in these leaves. Lower Pn partly resulted from the lower actual photochemical efficiency of PSII in developing leaves, as more excited energy was dissipated through non-photochemical quenching. The development of primary photochemical reaction and electron transport in the donor side of PSII was completed in the initiating leaves. However, the development of electron transport in the acceptor side of PSII was not accomplished until leaves were fully expanded, indicated by the change in probability that an electron moves further than primary quinone (ψo). PSI activity changed in parallel with ψo suggesting that PSI cooperated well with PSII during leaf expansion. It should be stressed that the development of carbon fixation process was later than primary photochemical reaction but earlier than photosynthetic electron transport during leaf expansion. The later development of photosynthetic electron transport may reduce the production of reactive oxygen species from Mehler reaction, particularly under low carbon fixation.     

Soybean leaf nitrogen,chlorophyll content,and chlorophyll <Emphasis Type="Italic">a/b</Emphasis> ratio

The objective of this study was to assess genotypic variation in soybean chlorophyll (Chl) content and composition, and to test if these data could be used as a rapid screening method to predict genotypic variation in leaf tissue N content. Chl contents and composition were examined among 833 soybean (Glycine max L. Merr.) accessions and related to SPAD meter readings and leaf N content. In the initial year of the study (2002), the relationship between leaf Chl and leaf N contents (r ² = 0.043) was not sufficiently close for Chl to be useful as a predictive tool for leaf N content. Therefore, leaf N content was not determined in 2004 but samples were again collected for determination of Chl content and composition. In 2002, the soybean accessions separated into two distinct groups according to leaf Chl a/b ratios, with the majority of a mean ratio of 3.79. However, approximately 7 % (60) of the genotypes could be readily assigned to a group with a mean Chl a/b ratio of 2.67. Chl a/b analyses in 2004 confirmed the results obtained in 2002 and of 202 genotypes, all but 6 fell into the same group as in 2002.     

Relationship between photosynthetic pigments and chlorophyll fluorescence in soybean under varying phosphorus nutrition at ambient and elevated CO<Subscript>2</Subscript>

To assess the relationship between chlorophyll (Chl) fluorescence (CF) and photosynthetic pigments, soybean was grown under varying phosphorus (P) nutrition at ambient and elevated CO₂ (EC). The EC stimulated, but P deficiency decreased plant height, node numbers, and leaf area concomitantly with the rates of stem elongation, node addition, and leaf area expansion. Under P deficiency, CF parameters and pigments declined except that carotenoids (Car) were relatively stable indicating its role in photoprotection. The CF parameters were strongly related with Chl concentration but not with Chl a/b or Car. However, total Chl/Car showed the strongest association with CF parameters such as quantum efficiency and yield of photosystem II. This relationship was not affected by CO₂ treatment. The high correlation between CF and total Chl/Car underscores the significance of the quantification of both, Chl and Car concentrations, to understand the photochemistry and underlying processes of photoprotection and mechanisms of excess energy dissipation in a given environment.