Performance index in assessing the physiological state of trees in urban ecosystems

Based on PAM and PEA measurements of fluorescence of bark chloroplasts, we have compared the information capacity of the methods for assessing the physiological state of Tilia cordata Mill. by the maximal quantum efficiency of PS II photochemistry (F _v/F _m) and by the performance index (PI). The measurements were made on annual shoots of linden trees growing in different environs. It was shown that the chlorophyll content in the bark of shoots growing near a busy urban street was twice less than in controls growing out of town. For the trees in the unfavorable environment, a small decrease in (F _v/F _m) was registered, and there was a significant statistical scatter in these values as compared with controls. The PI and its constituent parameters calculated from fluorescence induction curves (PEA method) are more informative and allow recognizing changes in the primary energy conversion processes in PS II when they are still small. Thus, PI can be used as a sensitive, robust, and rapid test to evaluate the physiological state of trees and other plant objects even under minor environmental changes.     

Seasonal Variation of Photoinhibition of Photosynthesis in Bark from Populus Tremula L.

In the bark of Populus tremula L. photochemical efficiency of photosystem 2 (PS2) determined as Fv/Fm decreased during winter. The strongest reduction was found after cold periods. The degree of reduction depended on irradiance since the lowest levels of Fv/Fm were found on the sun-exposed side of the stem and below thin phellem. Therefore, photoinhibition was partly responsible for the reduction in Fv/Fm. The photochemical efficiency of PS2 recovered in late April about a month before the trees got leaves. In the laboratory, Fv/Fm recovered within about a week under low irradiance at 20 °C. Rapid recovery of photochemical efficiency of PS2 in the bark may be important to reduce respiratory loss of CO2 from the stem before the trees get leaves.     

极小种群海南假韶子叶片光合特性和叶绿素荧光参数的动态变化

探讨海南省极小种群物种海南假韶子(Paranephelium hainanensis)的光合生理特性,以期为该物种的保护和利用提供科学依据。应用Li-COR便携式光合仪和FC1000-H便携式植物荧光成像系统测定海南假韶子的光合特性、叶绿素荧光参数的动态变化。结果表明:海南假韶子成年树和林下幼苗在7月和11月时净光合速率(P_n)和蒸腾速率(T_r)的日变化均呈明显"双峰"曲线,成年树的最大P_n达9.24μmol·m^-2·s^-1,最大T_r为3.34μmol·m^-2·s^-1,其光合能力显著强于幼苗;海南假韶子成年树初始荧光值(F₀)在7月和11月最大值分别为323.04和135.87,F_m在7月和11月最大值分别为502.78和307.76,但幼苗的F₀和F_m均低于成年树;成年树F_v/F_m...     

Photosynthetic Properties of Photosystem II in Arabidopsis thaliana lpa1 Mutant

In a previous study, we characterized a high chlorophyll fluorescence lpa1 mutant of Arabidopsis thaliana, 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 lpa1 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 wild-type 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 PSII protein accumulation further confirmed that the amount of PSII reaction center protein is correlated with changes in Fv/Fm in lpa1 plants. Thus, the assembled PSII in the mutant was functional and also showed increased photosensitivity compared with wild-type plants.(Author for correspondence. Tel: +86 (0)10 6283 6256; Fax: +86 (0)10 8259 9384; E-mail: zhanglixin@ibcas.ac.cn)     

草莓叶片光合作用对强光的响应及其机理研究

用便携式调制叶绿素荧光仪和光合仪研究了强光下草莓叶片荧光参数及表观量子效率的变化.结果表明,Fm、Fv/Fm、PSⅡ无活性反应中心数量和Q_A的还原速率在强光下降低,在暗恢复时升高;而PSⅡ反应中心非还原性Q_B的比例在强光下增加,在暗恢复时降低.上述荧光参数的变化幅度均以强光胁迫或暗恢复的前10 min最大.强光下Φ_PSII、ETR和qP先升高后降低,但qN先大幅度降低,然后小幅回升.强光处理4 h后,丰香和宝交早生的表观量子效率(AQY)分别降低了20.9%和37.5%;qE(能量依赖的非光化学猝灭)为NPQ(非光化学猝灭)的最主要成分.强光胁迫下丰香的Fo、Fm、Fv/Fm、Φ_PSII、ETR和AQY的变化幅度均明显比宝交早生小.DTT处理后,草莓叶片的Fm和Fv/Fm明显降低,Fo显著升高.可以认为,依赖叶黄素循环和类囊体膜质子梯度两种非辐射能量耗散在草莓叶片防御光损伤方面起着重要作用,丰香的光合机构比宝交早生更耐强光.     

Inhibition of CO2-fixation and its effect on the activity of Photosystem II,on D1-protein synthesis and phosphorylation

To study the effects of limitations in the Calvin-cycle on Photosystem (PS) II function and on its repair by D1-protein turnover, glycerinaldehyde (DLGA) was applied to 1 h dark-adapted pea leaves via the petiole. The application resulted in a 90% inhibition of photosynthetic oxygen evolution after 90 min illumination at either 120 or 500 µmol m^–2 s^–1. In the control leaves an increase of light-dependent oxygen production to 147 and 171% was observed after 90 min illumination. According to chlorophyll fluorescence quenching analysis the inhibition of photosynthetic electron transport by DLGA led to a substantial increase in the reduction state of the primary quinone acceptor of PS II, QA, and to a rise in membrane energetisation. However, PS II functionality was hardly affected by DLGA at the low light intensity as indicated by the constant high yield of variable fluorescence, Fv/Fm. Only at 500 µmol m^–2 s^–1 a 15% loss of Fv/Fm was observed in the presence of DLGA indicating that inactivated PS II centres had accumulated. The control leaves also showed a slight loss of Fv/Fm which did not affect photosynthetic electron transport due to a faster reoxidation of QA. The relative stability of PS II function in the presence of DLGA could not be ascribed to an increased repair by the rapid turnover of the D1-protein. Radioactive pulse-labelling studies with [14C] leucine in combination with immunological determination of the protein content revealed that both synthesis and degradation of the protein were inhibited in DLGA-treated leaves whereas in the control leaves a stimulation of D1-protein turnover was observed. The changes of D1-protein turnover could be explained by differences in the occupancy state of the QB-binding niche. A relation between the phosphorylation status of the PS II polypeptides and the turnover of the D1-protein could not be established. As shown by radioactive labelling with [32P]i, addition of DLGA led to an increase in the phosphorylation level of the PS II polypeptides D1 and D2 at the low light intensity when compared to the non-treated control. At the higher light intensity the phosphorylation level of the PS II polypeptides in control and DLGA-treated leaves were identical in spite of the substantial differences in D1-protein turnover.     

Effects of Strong Light and Active Oxygen on Photosynthesis in Soybean

With the use of chlorophyll fluorescence technique, it was found that the net photosynthetic oxygen evolution rate decreased after strong light (2 000 μmol· m-2·2-1 ) treatment for two hours in soybean ( Glycine max L. ) leaves. The chlorophyll fluorescence parameters, Fm/Fo, Fv/Fm, ФPSII, qp and qN decreased along with the increase of light intensity. In strong light, exogenous active oxygen H202、·OH and 'O2 were harmful to soybean leaves. The destruction of 'O2 and·OH to leaves was most evident, as was shown that Fv/Fm and PS H decreased significantly. The antioxidants DABCO, mannitol, ascorbate and histidine protected the leaves, but weakly, from strong light. In darkness, the SOD inhibitor sodium diethyldithiocar- bamate (DDC) had no significant effect on Fm/Fo and Fv/Fm, but NAN,, the ascorbate peroxidase (APX)inhibitor, significantly decreased Fm/Fo, Fv/Fm and ФPS II. In strong light, however, beth DDC and NaN3 reduced the above-mentioned fluorescence parameters, but NaN3 was more effective than DDC. The results suggested that photoinhibition did take place in soybean leaves under strong light, and it was related to active oxygen in vivo.     

高温对仁用杏光合特性及PSⅡ光化学活性的影响

为探讨高温胁迫下仁用杏叶片的光合适应机制,以科尔沁沙地生长的4年生'超仁'仁用杏为试材,设置环境温度为25℃、30℃、40℃和50℃处理,利用气体交换技术和快速叶绿素荧光诱导动力学曲线分析技术(JIP-test),研究了仁用杏叶片光合特性和PSⅡ光化学活性.结果表明:在一定温度范围内,随着温度升高,仁用杏通过提高光合色素含量和比例来维持光能的吸收、传递和转换能力,从而保证光合机构正常运转;当高温超过叶片自身生理调节限度后,叶绿素发生分解、净光合速率(Pn)明显下降、胞间CO2浓度(Ci)上升,说明光合作用的下降是由叶肉因素造成的.温度40℃导致单位面积有活性反应中心数量(RC/CSo)显著下降;而50℃高温下荧光诱导曲线中K点(Wk)和J点(Vj)明显增加,高温对仁用杏叶片放氧复合体(OEC)、受体侧和PsⅡ反应中心造成了伤害.此外,50℃高温还导致初始荧光(Fo)显著升高,为对照的2.26倍,PSⅡ最大光化学效率(Fv/Fm)和光化学性能指数(PI/ABS)分别下降为对照的37.9%和10.3%.高温损害了PSⅡ供体侧和受体侧的功能,造成光合效率下降,这是高温胁迫对仁用杏叶片光合机构伤害的主要机制之一.     

干旱胁迫对不同葡萄砧木光合特性和荧光参数的影响

干旱胁迫导致葡萄砧木实生苗叶片光合能力下降.在正常供水和轻度干旱下,砧木的P_n 以3309C最高,其次是1103P,420A较低,各砧木的G_s和T_r差异不显著;中度干旱下,则以1103P的P_n最高,3309C最低;而严重干旱胁迫下,1103P的P_n比3309C高出124%,水分利用效率是3309C的1.95倍.干旱胁迫下,3种砧木的共同趋势是可变荧光 (F_o) 升高,最大荧光 (F_m)、实际光能转化效率 (ФPSⅡ）和可变荧光与最大荧光比 (F_v/F_m) 降低,但品种变幅不同.中度干旱使3309C的F _o升高17.1%,F_v/F_m降低了8.5%,而1103P的F_o升高6.8%,F_v/F_m降低了5.8%;严重干旱则使3309C的F_o升高36.2%,F_v/F_m降低了20.1%,而1103P的F_o升高9.9%,F_v/F_m降低了10.2%.干旱胁迫对不同葡萄砧木光合和荧光参数的影响与其抗旱性密切相关,其中F_v/F_m和P_n的相关系数最大（r=0.9883）.     

模拟干旱胁迫下构树和桑树的生理特征比较

在不同浓度聚乙二醇(PEG 6000)的处理下,测定构树和桑树的碳酸酐酶活性、光响应曲线、二氧化碳响应曲线和叶绿素荧光等指标,比较它们的抗干旱能力.结果表明:(1)构树的碳酸酐酶活力变化不显著,而桑树的碳酸酐酶活力不同的PEG 6000浓度间差异较大.(2)构树的净光合速率受PEG 6000的影响较小,而桑树受到抑制较...     

温州蜜柑叶片光合作用光抑制的保护机理

晴天条件下,使用便携式调制荧光仪和分光光度计观察了温州蜜柑叶片光合作用光抑制发生过程中几个主要荧光参数（初始荧光F0、最大荧光Fm、PSⅡ的光化学效率Fv/Fm、非光化学猝灭qN及其快相qNf和慢相qNs）、电子传递速率（ETR）和玉米黄素相对含量的日变化,结果表明,随着光强的增强,ETR、qN及其qNr与qNs以及玉米黄素相对含量升高,Fv/Fm、Fm和F0下降。用DTT处理后,qNs较对照明显下降,F0较对照明显上升,可以认为,柑橘在光合作用日变化中存在依赖于叶黄素循环和类囊体膜质子梯度两种非辐射能量耗散方式,而且它们在防御光破坏方面起着重要作用。     

Temperature, evapotranspiration and primary photochemical responses of apple leaves to hail

The objective of this work was to examine immediate physiological plant responses to hail and subsequent recovery in terms of evapotranspiration, leaf temperature and primary photochemical processes using apple as a model crop. Thermal emission pictures were taken in darkness to avoid interference from stomatal movements; temperature gradients were identified in concentric rings around sites of hail injury, with a distinct drop in temperature of up to 2.3 degrees C in the center immediately after the induced hail injury. This was due to enhanced evapotranspiration from the injured tissue. Six to twelve minutes after hail injury, the initial decrease in leaf temperature partially reversed. Chlorophyll fluorescence kinetics of light-adapted leaves showed a dramatic decrease in effective photosynthetic electron transport rate (ETR), from 20.5 to 9.0 micromol electron m(-2)s(-1) within 5 min from hail injury, and a rapid recovery to 14.1 micromol electron m(-2)s(-1) within the next 5 min. After 7h, ETR partially recovered to 17.4 micromol electron m(-2)s(-1). An initial drop in non-photochemical efficiency (NPQ) from 1.07 to 0.90 units within 5 min after hail injury was followed by a sharp increase to 1.67 units after another 5 min. During the next hour, NPQ gradually decreased to the initial level. This indicates increased thermal dissipation in photosystem II (PS II) as a protective mechanism against incident excessive energy in the leaves with closed stomata for 1h after hail injury. In contrast to the fluorescence kinetics of light-adapted leaves, maximum quantum yield Fv/Fm of PSII in the dark-adapted state remained unchanged at 0.79-0.81 relative units for the first 5 min after hail injury. Thereafter, Fv/Fm slowly declined to 0.75 within 1h, and to a trough of 0.73 at 3h. Seven hours after hail injury, Fv/Fm values were at 0.76, indicating partial recovery of PS II efficiency. The discrepancy in the dynamics of ETR and Fv/Fm responses may be explained by the formation of alternative electron sinks such as reactive oxygen species, particularly superoxides, which withdraw electrons from the photosynthetic transport, resulting in apparently higher values of calculated ETR.     

Physiological and oxidative stress responses of baldcypress in response to elevated salinity: linking and identifying biomarkers of stress in a keystone species

Globally, saltwater intrusion associated with sea level rise is threatening the vitality of coastal freshwater wetland communities. In the current study, we investigated the impacts of salinity stress on Baldcypress (Taxodium distichum (L.) Rich), a tree common to coastal freshwater wetlands within the southeastern USA. Salinity-induced responses of saplings and adult trees were assessed in a greenhouse and field-based study, respectively. In the greenhouse study, saplings maintained under mesohaline conditions (8 g L^?1) for 10 weeks exhibited a predictable physiological response characterized by decreased maximum quantum yield of photosystem II (Fv/Fm) and increased non-photochemical quenching. Changes in photochemistry were concomitant with increases in leaf sodium, hydrogen peroxide, and free proline content compared to saplings maintained in freshwater. A strong negative correlation existed between Fv/Fm and leaf hydrogen peroxide content. Salinity-stressed saplings also exhibited decreased activity of a low molecular weight peroxidase isozyme within leaf tissue. Taken together, the evidence suggests that H₂O₂ was maintained at marginally elevated levels in leaf tissue to elicit a physiological response. Adult trees sampled in situ displayed similar stress responses to elevated salinity as saplings from the greenhouse study. Specifically, trees sampled at a basin swamp exhibited decreased Fv/Fm and increased non-photochemical quenching, lipid peroxidation, and free proline content in leaf tissue compared to trees at other sites. Thus, coupling chlorophyll fluorescence parameters with stable biomarkers show promise in detecting sub-lethal salinity stress for plants in situ.     

Photochemical Efficiency of PSⅡand Membrane Lipid Peroxidation in Leaves of indica and japonica Rice (Oryza sativa) Under Chilling Temperature and Strong Light Stress Conditions

Relationships between fluorescence parameters and membrane lipid peroxidation in leaves of indica and japonica rice (Oryza sativa L.) during later growth stage were studied under chilling temperature and strong light stress conditions. Results showed that D1 protein contents of PSⅡ in photosynthetic app aratus dropped, the generation of antheraxanthin (A) and zeaxanthin (Z)of xanthophyll cycle were inhibited partly, PSⅡ photochemical efficiency （Fv/Fm）and non photochemical quenching (qN) were also decreased obviously. In addition, endogenous active oxygen scavenger—superoxide dismutase (SOD) reduced, superoxide anion radical (O[SX(B-*3)-[]·[SX]]2) and malondialdehyde (MDA) accumulated, as a result, photooxidation of leaves occurred under chilling temperature and strong light stress conditions. Obvious differences in the changes of the above mentioned physiological parameters between indica and japonica rice were observed. Experiments in leaves treated with inhibitors under chilling temperature and strong light conditions showed that indica rice was more sensitive to chilling temperature with strong light and subjected to photooxidation more than japonica rice. Notable positive correlation between D1 protein contents and Fv/Fm or (A+Z)/(A+Z+V), and a marked negative correlation between Fv/Fm and MDA contents were obtained by regression analysis in indica and japonica rice during chilling temperature and strong light conditions. According to the facts mentioned above, it was inferred that PSⅡ photochemical efficiency（Fv/Fm） was the key index to forecast for the prediction of photooxidation under stress circumstances and the physiological basis were the synthetic capacity of D1 protein and the protection of xanthophyll cycle.     

高温胁迫对柑橘光合速率和光系统Ⅱ活性的影响

用红外CO2分析仪和叶绿素荧光仪测定了温州蜜柑和脐橙叶片的净光合速率(Pn)、初始荧光(Fo)、最大光能转换效率(Fv／Fm)及电子传递速率(ETR)．结果表明,与常温(25℃)相比,高温胁迫(38～40℃)使温州蜜柑和脐橙叶片的Pn、Fv／Fm及ETR下降,Fo升高．胁迫25d后温州蜜柑和脐橙叶片的Pn分别下降55．6％和39．8％．Fv／Fm下降22．0％和6．7％,ETR下降55．0％和41．5％,Fo分别上升了113．8％和14．9％．柑橘经高温胁迫后,在25℃下处理10d,叶片的Pn、Fv／Fm、Fo及ETR恢复明显．这些结果说明柑橘的光合速率下降与PSⅡ反应中心失活有关．     

不同品种美国山核桃叶绿素荧光参数日变化的研究

以湖南省永州市冷水滩采穗圃中的美国山核桃为试材,研究了叶绿素荧光参数的日变化规律。结果表明:初始荧光(Fo)、最大荧光(Fm)、PSII原初光能转化效率(Fv/Fm)、光合量子产额(Yield)、光化学猝灭系数(qP)、非光化学猝灭系数(qN)和表观电子传递速率(ETR)均存在着明显的日变化。其中Fv/Fm、Fm、Yield、qP均呈先下降后上升的趋势,在中午强光下降低到最低值;qN则呈先上升后下降的趋势,在中午时分达到峰值;Fo呈下降趋势,部分品种傍晚稍有回升,但仍比早晨低;ETR日变化呈双峰曲线。不同品种间Fv/Fm、Yield、ETR、qP、qN对光强和温度的响应也存在着明显差异,可作为鉴定品种耐光抑制能力大小的指标。     

海水处理对不同产地菊芋幼苗光合作用及叶绿素荧光特性的影响

种植抗盐耐海水经济作物是合理开发利用沿海滩涂和海水资源、培育耐盐植物的有效措施之一。该研究以不同产地菊芋(Helianthus tuberosus)为试验材料研究了海水处理对菊芋幼苗生长、光合作用和叶绿素荧光特性的影响。结果表明:1)随着海水浓度的增加,各地菊芋幼苗根、地上部的鲜重和干重均降低,但盐城菊芋幼苗地上部和根鲜重及干重降低的幅度小于武威和烟台菊芋幼苗。2)随着海水浓度的增加,各地菊芋叶片的净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)、气孔导度(G_s)和气孔限制值(L_s)均降低,而细胞间隙CO₂浓度(C_i)增大,且在各处理下盐城菊芋较武威和烟台菊芋叶片P_n和T_r大,而盐城菊芋在15%海水处理下,WUE和C_i较武威及烟台菊芋低,G_s和L_s较武威和烟台菊芋高。3)随着海水浓度的增加,各地菊芋叶片的初始荧光(F_o)、最大荧光(F_m)、可变荧光(F_v)、恒态荧光(F_s)、恒态荧光与初始荧光差值(ΔF_o)、PSⅡ潜在光化学效率(F_v/F_o)和PSⅡ最大光化学效率(F_v/F_m)均降低,且在各处理下盐城菊芋较武威和烟台菊芋叶片F_m、F_v、F_s、F_v/F_o大。随着海水浓度的增加,盐城菊芋叶片电子传递速率(ETR)、光化学荧光猝灭系数(q_P)和光化学速率变化幅度不大,武威和烟台菊芋在30%海水处理下显著下降,较盐城菊芋小,各处理下菊芋叶片的PSⅡ实际光化学效率(Φ_PSⅡ)变化也不一致,盐城和武威菊芋叶片的Φ_PSⅡ在15%海水处理较0和30%海水处理下大,而烟台菊芋叶片的Φ_PSⅡ在0海水处理下最大。4)随着海水浓度的增加,各地菊芋叶片的叶绿素a(Chla)含量均降低,而叶绿素b(Chlb)含量没显著差异,且在各处理下盐城菊芋较武威和烟台菊芋叶片Chla含量大,武威和盐城菊芋叶片的Chla/Chlb比值均降低,烟台菊芋叶片的Chla/Chlb比值在0和15%海水处理下没差异。可见海水处理对菊芋幼苗生长发育、光合作用和叶绿素荧光特性均有影响,随海水浓度的增加,其效应越明显,但对各来源地菊芋幼苗的影响不一致,盐城菊芋幼苗表现为更耐海水。     

茄子光系统Ⅱ的热胁迫特性

以耐热性较弱的黑贝一号圆茄和耐热性较强的黑贝二号圆茄为试材,热胁迫处理后采用植物效率仪PEA进行快速叶绿素荧光诱导曲线及其参数测定.结果表明：当温度高于40 ℃,PSⅡ结构受热胁迫影响较为敏感,表现为初始荧光F_o缓慢上升;PSⅡ原初光化学效率F_v/F_m和ΔF/F_m′大幅度下降,且黑贝二号F_v/F_m的半衰时间T₅₀和ΔF/F_m′的半衰温度t₅₀分别大于黑贝一号.较高的热胁迫剂量（48℃处理5 min或44℃处理20～30min）下,快速荧光诱导动力学曲线呈现OKJIP型,在700μs处出现与放氧复合体失活有关的K相.黑贝一号在44 ℃下处理20 min才有K相出现,黑贝二号则晚10 min出现.与35℃相比,在48℃,特别是在52℃的较高剂量热胁迫下,Strasser能量流动模型参数中的DI_o/RC有大幅度地增加,体现了热耗散对PSⅡ的较强保护能力.随着热胁迫温度的升高和热胁迫时间的延长,两品种的无活性中心F_vi/Fv显著增加.     

水淹对水芹叶片结构和光系统Ⅱ光抑制的影响

通过探讨在水淹条件下水芹（Oenanthe javanica）叶片结构的变化以及出水对其光系统II功能和光抑制的影响,阐明水芹光合机构在水淹条件下及出水后死亡的可能原因。结果表明：水淹条件下新生沉水功能叶光系统Ⅱ（PSⅡ）最大光化学效率（Fv/Fm）、电子传递活性与对照叶片差异很小,但水淹使气生功能叶的Fv/Fm显著降低;植株总生物量呈负增长趋势;活体弱光条件下,沉水叶出水后2小时叶片相对含水量（RWC）和Fv/Fm无显著变化;中等光强和强光条件下其RWC和Fv/Fm迅速降低;离体条件下,5小时的中等光强对沉水叶的Fv/Fm影响不显著,在随后的弱光下能恢复到出水时的初始状态;强光能使沉水叶的Fv/Fm大幅降低,且弱光下不能恢复到出水时的初始水平;在解剖结构上,水芹沉水叶的叶片总厚度、上下表皮厚度和气孔大小都显著低于气生叶,而且沉水叶没有明显的栅栏组织分化,但是沉水叶上表皮的气孔密度显著高于气生叶。研究结果表明,水淹使水芹原气生叶PSⅡ功能迅速衰退,但对新生沉水叶片影响很小。水芹植株出水后,沉水叶片结构变化使其在光下保水能力下降,而强光导致了光合机构的光抑制和反应中心失活。田间条件下两者共同作用则加剧了对叶片光合机构的破坏,进而致使其死亡。     

Effect of methylmercury chloride on the primary photosynthetic activity of higher plants

The effect of methylmercury chloride (MeHg) on the fluorescence characteristics of pea seedling leaves and thylakoids isolated from these leaves was studied by the pulse-amplitude-modulation (PAM) fluorometric method. In 3-4 days after the addition of MeHg (20 microM) to the nutritious solution, the maximal (Fv/Fm) and real (under steady state actinic light illumination) (deltaF/F'm) quantum photochemical yield of PS II decreased. The nonphotochemical fluorescence quenching coefficient in control (qN) decreased after its maximum value has been reached. In MeHg-treated samples, this decrease was not observed, possibly due to the disturbance of delta pH energy transducing processes in ATP synthase. This was confirmed by the results of experiments on isolated thylakoids. After MeHg (5 microM) treatment of thylakoids, the photophosphorylation rate and light-triggered Mg2+-dependent H+-ATPase activity were suppressed by 20-40%, depending on the duration of MeHg exposure. However, in experiments with isolated thylakoids, no decrease either in the electron transport rate or in the Fv/Fm ratio was observed. In total, the results obtained allow one to assume that MeHg at concentrations and time duration used directly damages the coupling complex. The PS II inactivation in leaves and algae cells may be a result of the oxidative stress processes.