Prompt chlorophyll fluorescence as a tool for crop phenotyping: an example of barley landraces exposed to various abiotic stress factors

The study examined photosynthetic efficiency of two barley landraces (cvs. Arabi Abiad and Arabi Aswad) through a prompt fluorescence technique under influence of 14 different abiotic stress factors. The difference in the behavior of photosynthetic parameters under the same stress factor in–between cv. Arabi Abiad and cv. Arabi Aswad indicated different mechanisms of tolerance and strategies for the conversion of light energy into chemical energy for both the landraces. This study confirmed the suitability of some chlorophyll fluorescence parameters as reliable biomarkers for screening the plants at the level of photosynthetic apparatus.     

Effects of salt stress on photosystem II efficiency and CO2 assimilation of two Syrian barley landraces

The photosynthetic activity of two Syrian barley landraces, Arabi (A.) Aswad and A. Abiad, grown under 120 mM NaCl, was studied, using gas exchange and chlorophyll (Chl) a fluorescence transient (OJIP) measurements. Salt treatment of barley seedlings decreased both the rates of photosynthesis and photosystem II (PSII) activity, as evaluated from chlorophyll fluorescence data. However, the noted decrease was dependent on the duration of the salt treatment and the barley cultivar. Several parameters (e.g., light absorption flux per cross section of leaf; time to reach maximum chlorophyll a fluorescence intensity; plastoquinone pool size; yield of heat loss; rate of reaction center closure; and the so-called Performance Index), calculated and inferred from Chl fluorescence measurements, and related to PSII activity, were affected after 24 h of salt application, but these changes were much more pronounced after 7 days of salt treatment. Similar changes were found for measured gas exchange parameters: CO₂ uptake (photosynthetic) rate and stomatal conductance. The photosynthetic apparatus of the cultivar variety (c.v.) Arabi Aswad was found to be much more tolerant to salt treatment, compared with c.v. Arabi Abiad. After 7 days of salt treatment, the latter showed a very high value of the initial (minimal) fluorescence (F_o) and then essentially almost flat fluorescence transient curve; this result may be due to several causes that include structural changes as well as changes in the rate constants of different dissipative processes. The parameters that were most affected, by salt treatment, were: the time needed to reach the maximal chlorophyll fluorescence (F_m), and the inferred oxygen evolving complex activity (F_v/F_o, where F_v, is F_m − F_o), and the calculated Performance Index (PI_ABS) that depends on the efficiency and the yield of energy transfer and primary photochemistry. We suggest that the early reactions of the photosynthetic apparatus of barley plants could play a key role in their tolerance to salt stress. Further, we found that the first stage of salinity effect on photosynthesis of barley plants is related to stomatal conductance limitation rather than to PSII activity reduction. Thus, on the basis of our results on the two barley landraces, we recommend the use of a combination of gas exchange measurements along with the analysis of the OJIP fluorescence transient for the detection of salt stress-induced changes in plants.     

The change of chlorophyll fluorescence parameters in winter barley during recovery after freezing shock and as affected by cold acclimation and irradiance

The change of chlorophyll fluorescence parameters in froze leaves of 3 leaf-age seedlings were examined using two winter barley cultivars (Chumai 1 and Mo 103) differing in cold tolerance to investigate physiological response to low temperature as affected by cold acclimation (under 3/1 degrees C, day/night for 5 days before freezing treatment) and irradiation size (high irradiance: 380+/-25 micromol m(-2)s(-1) and low irradiance: 60+/-25 micromol m(-2)s(-1)) during recovery. The results showed that non-lethal freezing shock (exposed to -8 degrees C for 18 h) did not obviously affect maximum quantum efficiency in photosystem II (PSII), but dramatically increased non-photochemical quenching and reduced effective quantum yield in PSII. Cold acclimation significantly improved stability of photosynthetic function of leaves after freezing stress through buffering excessive energy and alleviating photoinhibition during recovery, indicating it increased recovery ability of barley plants from freezing injury. High irradiance was quite harmful to the stability of PSII in barley plants during recovery from freezing injury. The electron transport rate of PSII varied with cold-acclimation, irradiance and genotype. Cold acclimation caused significant increase in electron transport rate of PSII for relatively tolerant cultivar Mo 103, but not for relatively sensitive cultivar Chumai 1. It can be concluded that some chlorophyll fluorescence parameters during recovery from freezing shock may be used as the indicators in identification and evaluation of cold tolerance in barley.     

Response of the photosynthetic apparatus of cotton (Gossypium hirsutum) to the onset of drought stress under field conditions studied by gas-exchange analysis and chlorophyll fluorescence imaging.

The functioning of the photosynthetic apparatus of cotton (Gossypium hirsutum) grown during the onset of water limitation was studied by gas-exchange and chlorophyll fluorescence to better understand the adaptation mechanisms of the photosynthetic apparatus to drought conditions. For this, cotton was grown in the field in Central Asia under well-irrigated and moderately drought-stressed conditions. The light and CO(2) responses of photosynthesis (A(G)), stomatal conductance (g(s)) and various chlorophyll fluorescence parameters were determined simultaneously. Furthermore, chlorophyll fluorescence images were taken from leaves to study the spatial pattern of photosystem II (PSII) efficiency and non-photochemical quenching parameters. Under low and moderate light intensity, the onset of drought stress caused an increase in the operating quantum efficiency of PSII photochemistry (varphi(PSII)) which indicated increased photorespiration since photosynthesis was hardly affected by water limitation. The increase in varphi(PSII) was caused by an increase of the efficiency of open PSII reaction centers (F(v)'/F(m)') and by a decrease of the basal non-photochemical quenching (varphi(NO)). Using a chlorophyll fluorescence imaging system a low spatial heterogeneity of varphi(PSII) was revealed under both irrigation treatments. The increased rate of photorespiration in plants during the onset of drought stress can be seen as an acclimation process to avoid an over-excitation of PSII under more severe drought conditions.     

塔里木河下游地下水位对柽柳叶绿素荧光特性的影响

选取塔里木河下游3处地下水埋深6m的监测井位作为研究点,结合典型生态监测断面的地下水位监测数据,分析不同地下水埋深处柽柳的叶绿素荧光特性和光系统的光合活性.结果表明:随着地下水埋深加大和干旱胁迫加剧,柽柳叶片的实际光化学效率、电子传输速率和光化学猝灭等参数普遍下降;非光化学猝灭和调节性能量耗散量子产量等参数显著升高,而最大光量子产量总体处于相对适宜状态.干旱胁迫下柽柳的PSII光合活性随地下水埋深增大而下降,捕获光能的过剩程度加剧,发生光抑制的几率增大,其自身良好的抗旱性和自我调节机制,使光系统II尚未发生显著光损伤.     

Loss of the precise control of photosynthesis and increased yield of non‐radiative dissipation of excitation energy after mild heat treatment of barley leaves

The after effects of a short exposure of intact barley leaves to moderately elevated temperature (40°C, 5 min) on the induction transients and the irradiance dependencies of photosynthesis and chlorophyll fluorescence are presented. This mild heat treatment strongly reduced the oscillations in the rate of photosynthesis and in the yield of chlorophyll fluorescence. However, only a 25% irreversible inhibition of maximum photosynthetic capacity of photosystem II (PSII) measured by oxygen evolution was produced and the intrinsic quantum yield of PSII measured by the chlorophyll fluorescence ratio (F_m‐ F_o)/F_m decreased by only 15%. In contrast, the above treatment increased radiationless dissipation processes in PSII by a factor of two. In heat‐treated leaves, photosynthesis was not saturated even by strong light. Both ΔpH‐dependent quenching of excitons in PSII (including formation of zeaxanthin) and state 1/state 2 transition were found to be stimulated. Heat exposure enhanced the control of PSII activity by PSI, as evidenced by a significant increase in the quenching effect of far‐red light on the maximum yield of chlorophyll fluorescence. It was deduced that after mild heat treatment, the photosynthetic apparatus in leaves lacks the precise coordinating control of electron transport and carbon metabolism owing to the inability of PSII to support electron transport at a level adequate for carbon metabolism. This effect was not related to the small irreversible thermal damage to PSII, but was rather due to a significant increase in non‐photochemical quenching of excitation energy.     

Heat stress induces an inhibition of excitation energy transfer from phycobilisomes to photosystem II but not to photosystem I in a cyanobacterium Spirulina platensis.

The effects of high temperature (30-52.5 degrees C) on excitation energy transfer from phycobilisomes (PBS) to photosystem I (PSI) and photosystem II (PSII) in a cyanobacterium Spirulina platensis grown at 30 degrees C were studied by measuring 77 K chlorophyll (Chl) fluorescence emission spectra. Heat stress had a significant effect on 77 K Chl fluorescence emission spectra excited either at 436 or 580 nm. In order to reveal what parts of the photosynthetic apparatus were responsible for the changes in the related Chl fluorescence emission peaks, we fitted the emission spectra by Gaussian components according to the assignments of emission bands to different components of the photosynthetic apparatus. The 643 and 664 nm emissions originate from C-phycocyanin (CPC) and allophycocyanin (APC), respectively. The 685 and 695 nm emissions originate mainly from the core antenna complexes of PSII, CP43 and CP47, respectively. The 725 and 751 nm band is most effectively produced by PSI. There was no significant change in F725 and F751 during heat stress, suggesting that heat stress had no effects on excitation energy transfer from PBS to PSI. On the other hand, heat stress induced an increase in the ratio of Chl fluorescence yield of PBS to PSII, indicating that heat stress inhibits excitation energy transfer from PBS to PSII. However, this inhibition was not associated with an inhibition of excitation energy transfer from CPC to APC since no significant changes in F643 occurred at high temperatures. A dramatic enhancement of F664 occurring at 52.5 degrees C indicates that excitation energy transfer from APC to the PSII core complexes is suppressed at this temperature, possibly due to the structural changes within the PBS core but not to a detachment of PBS from PSII, resulting in an inhibition of excitation energy transfer from APC to PSII core complexes (CP47 + CP43). A decrease in F685 and F695 in heat-stressed cells with excitation at 436 nm seems to suggest that heat stress did not inhibit excitation energy transfer from the Chl a binding proteins CP47 and CP43 to the PSII reaction center and the decreased Chl fluorescence yields from CP43 and CP47 could be explained by the inhibition of the energy transfer from APC to PSII core complexes (CP47 + CP43).     

CaCl_2对UV-B辐射下菠菜叶片光合特性的影响

以"丹麦旺盛菠菜"为材料,通过UV-B和CaCl2复合处理,测定光合色素含量、Hill反应活力、叶绿素荧光、MDA含量和抗氧化酶活性等参数,探讨了CaCl2对UV-B辐射下菠菜叶片电子传递链和光合膜酶保护系统的影响。结果表明,UV-B处理下,光合色素含量、chl/car、类囊体膜上PSII潜在活性(Fv/Fo)、光化学淬灭系数(qP)、非光化学淬灭系数(qN)、PSII光量子产量(ΦPSⅡ)、原初光能转化效率(Fv/Fm),以及Hill反应活力等降低,chla/chlb和MDA含量升高;喷洒CaCl2可不同程度缓解UV-B的伤害。不同处理下,POD、SOD和CAT活性的变化呈现补偿效应。UV-B强度与菠菜叶片PSII功能受损程度呈正相关,CaCl2则主要通过提高chlb含量、类囊体膜上的光量子产量和POD活性,以缓解伤害。重度UV-B辐射下,CaCl2使chlb含量显著提高可能是导致PSII捕光效率提高的重要因素。     

Effects of ozone exposure or fungal pathogen on white lupin leaves as determined by imaging of chlorophyll a fluorescence.

Chlorophyll fluorescence has been used routinely to investigate photosynthetic activity in plants subjected to both biotic and abiotic stresses. The aim of this work was to compare the perturbations in photosynthesis induced by ozone and by a pathogen. By using a conventional fluorometer a similar response pattern was observed in inoculated and O(3)-fumigated leaves. The application of chlorophyll fluorescence imaging provided further detailed information on the spatial-temporal heterogeneity of the response of white lupin leaves to fungal pathogen or to ozone fumigation. In particular, 48 h after artificial inoculation with the necrotrophic fungal pathogen Pleiochaeta setosa, the leaves showed a remarkable alteration in PSII operating efficiency (Phi(PSII)), which affected the whole surface. Afterwards, the infection site was surrounded by a ring of increased photosynthetic activity. The response of ozonated leaves was quite different. The reduction in Phi(PSII) was already evident 24h after fumigation; moreover, a distinct heterogeneity of the fluorescence yield was observed and the major veins displayed a lowered Phi(PSII).     

Photosynthetic acclimation of Chlorella saccharophila to heat stress

Photosynthesis is one of the most important metabolic processes of algae; which is altered as a stress response. During mass cultivation of algae, temperature rise and high light are major factors that affect biomass productivity. High temperature affects photosystem II (PSII) complex irreversibly, damaging intermolecular interactions in it. However, the impact of high temperature on photosynthesis is highly variable among different algal species, depending on the prior acclimation to environmental conditions they were exposed to. The acclimation plays an important role in combating high temperature stress via regulation of photosynthetic responses. Chlorophyll a fluorescence is a highly sensitive, non‐destructive and reliable tool for such measurements of photosynthetic parameters, which provides information about algal photosynthetic performance under given conditions. To understand the effect of heat stress on the responses of high light acclimated alga Chlorella saccharophila, chlorophyll a fluorescence transients were measured after heat exposure at 40°C. Our study demonstrates that rise in temperature for short duration; during open field cultivation reversibly affects the efficiency of PSII in light acclimated alga C. saccharophila. The effects of heat stress on chlorophyll a fluorescence in this alga, grown under high light (max‐1600 μmol photons m^?2 s^?1) are presented here; they are used to infer changes in photosynthetic process during its exposure to heat, as well as their recovery after 72 h. We speculate that heat resistance may have been acquired due to prior exposures to high light.     

Photorespiration and photoinhibition in the bracts of cotton under water stress

Gas exchange and chlorophyll fluorescence parameters of PSII were analyzed in the bracts and leaves of cotton plants after anthesis. Photosynthetic activity and photorespiration were measured in the leaves and bracts of cotton grown under either normal or reduced water-saving drip irrigation. The photosynthetic performance, amount of chlorophyll and Rubisco, and net photosynthesis were greater in the bracts than that in the leaves under water stress. The actual photochemical efficiency of PSII decreased in both the bracts and leaves after anthesis under reduced irrigation. However, the decrease was smaller in the bracts than in the leaves, indicating that the bracts experienced less severe photoinhibition compared to the leaves. The greater drought tolerance of bracts could be related to differences in relative water content, instantaneous water-use efficiency, and photorespiration rate. The ratio of photorespiration to net photosynthesis was much higher in the bracts than in leaves. Furthermore, water deficiency (due to the water-saving drip irrigation) had no significant effect on that ratio in the bracts. We hypothesized that photorespiration in the bracts alleviated photoinhibition and maintained photosynthetic activity.     

模拟酸雨胁迫下硅对髯毛箬竹光合特性的影响

以髯毛箬竹为试验材料,研究了模拟酸雨胁迫(pH 3.0)下硅对髯毛箬竹叶片叶绿素相对含量、光合作用日变化以及叶绿素荧光特性等的影响.结果表明:20和100 mg·L^-1 Na₂SiO₃预处理可以不同程度地抑制酸雨胁迫下髯毛箬竹叶片叶绿素含量的显著下降,且以100 mg·L^-1浓度处理效果最佳,叶绿素含量可提高22.7%,而高浓度(500 mg·L^-1)预处理则无缓解作用-酸雨胁迫下,髯毛箬竹光合“午休”现象加重,日平均净光合速率(P_n)、气孔导度(G_s)和气孔限制值(L_s)明显降低,而胞间CO₂浓度(C_i)增大,经过20～100 mg·L^-1硅预处理后,P_n、G_s、L_s不同程度增加,而C_i有所降低,且以100 mg·L^-1硅预处理效果最佳,日平均P_n增加39.2%.酸雨胁迫下,箬竹PSⅡ最大荧光(F_m)、最大光化学效率(F_v/F_m)、潜在活性(F_v/F_o)、有效光化学效率(F_v′/F_m′)、最大荧光产额(F_m′)、光化学淬灭系数(q_P)、非光化学淬灭系数(q_N)、PSII实际光化学效率(Φ_PSⅡ)降低,暗适应和光适应下的最小荧光产额F_o、F_o′ 则升高;而100 mg·L^-1硅预处理明显抑制了胁迫下各荧光参数的变化,F_v/F_m、F_v/F_o、F_v′/F_m′和Φ_PSⅡ分别增加35.2%、146.2%、55.0%和24.3%.说明外源适宜浓度硅预处理能有效地缓解酸雨胁迫导致的髯毛箬竹光合活性下降和光合系统损伤,从而提高胁迫下植物的光合能力.     

Foliar application of 24-epibrassinolide alleviates high-temperature-induced inhibition of photosynthesis in seedlings of two melon cultivars

Brassinosteroids (BRs), an important class of plant steroidal hormones, play a significant role in the amelioration of various biotic and abiotic stresses. 24-epibrassinolide (EBR), an active brassinosteroid, was applied exogenously in different concentrations to characterize a role of BRs in tolerance of melon (Cucumis melo L.) to high temperature (HT) stress and to investigate photosynthetic performance of HT-stressed, Honglvzaocui (HT-tolerant) and Baiyuxiang (HTsensitive), melon variety. Under HT, Honglvzaocui showed higher biomass accumulation and a lower index of heat injury compared with the Baiyuxiang. The exogenous application of 1.0 mg L^?1 EBR, the most effective concentration, alleviated dramatically the growth suppression caused by HT in both ecotypes. Similarly, EBR pretreatment of HTstressed plants attenuated the decrease in relative chlorophyll content, net photosynthetic rate, stomatal conductance, stomatal limitation, and water-use efficiency (WUE), as well as the maximal quantum yield of PSII photochemistry (F_v/F_m), the efficiency of excitation capture of open PSII center, the effective quantum yield of PSII photochemistry (Φ_PSII), photochemical quenching coefficient, and the photon activity distribution coefficients of PSI (α). EBR pretreatment further inhibited the increase in intracellular CO₂ concentration, leaf transpiration rate, minimal fluorescence of dark-adapted state, nonphotochemical quenching, thermal dissipation, and photon activity distribution coefficients of PSII. Results obtained here demonstrated that EBR could alleviate the detrimental effects of HT on the plant growth by improving photosynthesis in leaves, mainly reflected as up-regulation of photosynthetic pigment contents and photochemical activity associated with PSI.     

Chlorophyll organization in dark-grown and light-grown pine (Pinus brutia) and barley (Hordeum vulgare)

A study was conducted comparing the organization of chlorophyll during development of the photosynthetic apparatus in dark-grown and light-grown pine and barley. The rationale was that gymnosperms, but not angiosperms, have a capacity to synthesize chlorophyll in darkness. Seedlings of Pinus brutia were germinated and grown in darkness or under photoperiodic (day/night) conditions. The low-temperature (77 K) fluorescence spectra of newly-emerging dark-grown seedlings exhibited a single fluorescence band peaking at 678–679 nm, which decayed primarily with a ∼5.5 ns lifetime. Over the first few days of growth, the emission shifted to longer wavelengths and a subnanosecond lifetime component became prevalent. After several days of dark growth the emission spectrum and lifetime profile of the low temperature fluorescence came to resemble those of light-grown pine and barley. At room temperature, dark-grown pine showed little variable fluorescence, though addition of DCMU caused a substantial fluorescence rise. Illumination with moderate light for a few hours was sufficient to 'photoinduce' the appearance of normal variable fluorescence. At 77 K, DCMU-treated samples clearly showed a very long-lived (∼40 ns) fluorescence lifetime component in light-grown pine and barley. This component was undetectable in dark-grown pine. If, however, dark-grown samples were illuminated either before or after DCMU addition and then frozen to 77 K, the ∼40 ns lifetime component appeared at a fluorescence intensity similar to that in light-grown samples. These results are explained primarily in terms of photoactivation of the photosystem II (PSII) donor side. The temporary maintenance of PSII in an inactive, highly-quenched state is suggested to provide an available, yet protected precursor for active PSII.     

土壤水分对湿地松幼苗光合特征的影响

通过设置常规供水(CK)、轻度干旱(T1)、水饱和(T2)、水淹(T3)4个处理组,研究湿地松当年实生幼苗在不同土壤水分条件下的光合生理响应及叶绿素荧光特性。结果表明:不同水分处理对湿地松幼苗的叶片气体交换参数、水分利用效率(WUE)、光合色素、叶绿素荧光参数等指标有不同的影响;其中,T3的光合色素含量最低;T2、T3组的湿地松幼苗表现出较低的净光合速率(Pn)、电子传递速率(ETR)和PSⅡ光化学的量子效应(ΦPSⅡ),但与其他耐水淹植物相比,T3条件下的湿地松幼苗仍具有较高的Pn,说明湿地松幼苗具有较强的耐水淹能力;在T1条件下,湿地松幼苗具有较高的WUE和较低的蒸腾速率(Tr)、气孔导度(Gs)以对抗干旱的逆境,其Pn、PSⅡ最大光化学效率(Fv/Fm)、ETR和ΦPSII均有所下降,但仍能维持在相对正常的水平。研究证明,湿地松幼苗具有一定的耐淹耐旱特性,可运用于三峡库区消落带的植被重建。     

Responses of Jatropha curcas seedlings to cold stress: photosynthesis-related proteins and chlorophyll fluorescence characteristics

Photosynthesis-related proteins and PSII functions of Jatropha curcas seedlings under cold stress were studied using proteomic and chlorophyll fluorescence approaches. The results of chlorophyll fluorescence measurement indicated that electron transport flux per reaction center (ET_o/RC) and performance index (PI_ABS) were relatively sensitive to low temperature, especially at early stage of cold stress. The increase in O–J phase and decrease in J–I phase of chlorophyll fluorescence transient indicated a protection mechanism of J.   curcas to photoinhibition at early stage of cold stress. Eight photosynthesis-related proteins significantly changed during cold stress were identified using liquid chromatography MS/MS. Results of correlation analyses between photosynthesis-related proteins and chlorophyll fluorescence parameters indicated that (1) ATP synthase and Rieske FeS protein were significantly correlated with electron transport of reaction center in PSII; (2) precursor for 33-kDa protein was positively correlated with fluorescence quenching of the O–J and J–I phases and PI_ABS during cold stress, which implies that it might be related to multiple process in PSII; (3) contrary correlations were found between F_J − F_o and two enzymes in the Calvin cycle, and the relations between these proteins and PSII function were unclear. The combined study using proteomic approaches and chlorophyll fluorescence measurements indicated that the early-stage (0–12 h) acclimation of PSII and the late-stage (after 24 h) H₂O₂ scavenging might be involved in the cold response mechanisms of J.   curcas seedlings.     

干旱和复水对草莓叶片叶绿素荧光特性的影响

采用日本丰香草莓(Fragaria×ananassa Duch.cv.Toyonoka)品种进行实验,研究干旱和复水对其叶片叶绿素荧光特性的影响。结果表明,随着干旱胁迫程度的加剧,草莓叶片的最大荧光(Fm)、PSⅡ原初光能转化效率(Fv/Fm)、PSⅡ实际光化学效率(Yield)、光化学猝灭系数(qP)都随干旱胁迫的加剧而下降。干旱胁迫14d后,不同处理组草莓叶片的叶绿素荧光参数存在着显著的差异(P0.05)。复水后,低度胁迫和中度胁迫处理组能较快地恢复到正常水平,但重度胁迫组与对照组存在着显著的差异(P0.05)。     

Response of barley seedlings to UV-B radiation as affected by NaCl

The response of barley seedlings, subjected to 150 mmol/L NaCl for 4 days at different light regimes (4 d in the light, 4 d in darkness and a 12 h light/dark cycle) before UV-B radiation was investigated. NaCl treatment resulted in a decrease of total chlorophyll content and an increase in H2O2, free proline and lipid peroxidation, as quantified by measurement of malondialdehyde. Significantly more proline was accumulated in the light than in darkness. The combination of UV-B and NaCl treatment produced an additive effect on most of the parameters studied. UV-B radiation reduced the chlorophyll/carotenoids ratio and photochemical efficiency of PSII as estimated by chlorophyll fluorescence. NaCl pre-exposure decreased H2O2 generation and lipid peroxidation and alleviated the inhibitory effect of UV-B on PSII activity. Proline accumulated under salt stress conditions might be one of the reasons for the observed tolerance of barley seedlings to UV-B radiation.     

Characterization of target site of aluminum phytotoxicity in photosynthetic electron transport by fluorescence techniques in tobacco leaves

Aluminum (Al) toxicity limits crop yield in acidic soil through affecting diverse metabolic processes, especially photosynthesis. The aim of this work was to examine the effect of Al on photosynthetic electron transport in vivo as determined by chlorophyll fluorescence and delayed fluorescence of tobacco leaves. Results showed that Al treatment inhibited the photosynthetic rate and electron transfer, and decreased photosystem (PS) II photochemical activity in a time- and concentration-dependent manner, which could not be obviously alleviated by the addition of the reactive oxygen species (ROS) scavenger ascorbic acid (AsA). These results suggested that photosynthetic electron transfer chain components, especially PSII, might be directly damaged by Al instead of in an ROS-dependent manner. Furthermore, the fluorescence imaging and biochemical analysis exhibited that Al, after entering the cells, could accumulate in the chloroplasts, which paralleled the decreased content of Fe in the chloroplast. The changes in the chlorophyll fluorescence decay curve, the delayed fluorescence decay curve and the chlorophyll fluorescence parameters indicated that Al, through interacting with or replacing the non-heme iron between Q(A) and Q(B), caused the inhibition of electron transfer between Q(A) and Q(B), resulting in PSII photochemical damage and inhibition of the photosynthetic rate. In summary, our results characterized the target site of Al phytotoxicity in photosynthetic electron transport, providing new insight into the mechanism of Al phytotoxicity-induced chloroplast dysfunction and photosynthetic damage.     

高温胁迫下不同光强对‘赤霞珠’葡萄PSII活性及恢复的影响

本文研究了高温与不同光强结合处理对‘赤霞珠’葡萄叶片PSII活性及恢复的影响。结果表明,高温黑暗处理（40℃,0μmaol·m-2．s-1）导致叶片PSII最大光化学效率（Fv/Fm）、反应中心吸收的光能用于电子传递的量子产额（ψEo）与单位反应中心光能的传递（ETo/RC）降低明显,且无恢复趋势,K点相对荧光（Vk）、单位反应中心光能的吸收（ABS／RC）与捕获（TRo／RC）显著升高。高温弱光处理（40℃,200μmol·m-2．s-1）后的叶片PSII活性明显恢复,ETo／RC降低明显,TRo/RC无显著变化。高温强光（40℃,1600μmol·m-2．S-1）处理导致单位面积有活性反应中心数量（RC/CSm）抑制程度最大,恢复程度较低。实验结果说明,高温处理下黑暗对葡萄PSII功能活性及恢复均会造成抑制,而弱光可以显著缓解高温对葡萄叶片的胁迫作用,并促进PSII的恢复,强光导致胁迫下的PSII功能抑制最明显。