低温胁迫对水稻幼苗不同叶龄叶片叶绿素荧光特性的影响

以‘蜀恢162’(‘Shuhui 162’)、‘糯89-1’(‘Nuo 89-1’)、‘蜀恢162/糯89-1’(‘Shuhui 162/Nuo 89-1’)、‘奇妙香’(‘Qimiaoxiang’)和早黄矮(‘Zaohuang’ai’)5个水稻(Oryza sativa L.)品种(系)为研究对象,采用叶绿素荧光成像系统研究了低温(4℃)胁迫对水稻3叶期幼苗不同叶龄叶片叶绿素荧光特性的影响。结果表明:经低温胁迫处理后,5个水稻品种(系)幼苗3个叶龄叶片的各叶绿素荧光参数变化有明显差异,其中第一叶的各项参数均降至0。经低温处理后5个水稻品种(系)幼苗3片叶片的PSⅡ最大光化学量子产量(Fv/Fm)均明显小于对照(25℃),其中第一叶的降低幅度最大、第三叶最小。经低温胁迫处理后,5个水稻品种(系)幼苗第三叶的非光化学淬灭系数(qN)均显著大于对照,耐冷性品种‘糯89-1’幼苗第二叶的qN较对照显著增大,而其他水稻品种(系)幼苗第二叶的qN均显著小于对照;‘糯89-1’幼苗第二叶的光化学淬灭系数(qP)较对照略有增大,第三叶的qP显著大于对照;‘早黄矮’幼苗第三叶的qP也大于对照但差异不显著,而其余水稻品种(系)幼苗第二叶和第三叶的qP均显著小于对照。经低温胁迫后5个水稻品种(系)幼苗3片叶片的PSⅡ最大相对电子传递速率(rETRmax)和半饱和光强(Ik)均显著小于对照;除‘糯89-1’幼苗第三叶外,5个水稻品种(系)幼苗3片叶片的快速光响应曲线初始斜率(α)也均显著小于对照,总体上第一叶的rETRmax、Ik和α下降幅度最大、第三叶最小。研究结果揭示:受低温胁迫后,叶片自身生理差异是导致水稻幼苗不同叶龄叶片受伤害程度不同的主要因素。     

Effects of chilling and high temperatures on photosynthesis and chlorophyll fluorescence in leaves of watermelon seedlings

The effects of chilling (CT, day/night temperatures of 12/10 °C, an irradiance of 250 μmol m^?2 s^?1), chilling combined with a low irradiance (CL, 12/10 °C, 80 μmol m^?2 s^?1), and a high temperature (HT, 42/40 °C, 250 μmol m^?2 s^?1) on chlorophyll content, chlorophyll fluorescence, and gas exchange were studied in two watermelon cultivars, ZJ8424 and YS01, differing in their resistance. The chlorophyll content, net photosynthetic rate (P_N), stomatal conductance (g_s), and transpiration rate (E) decreased substantially, whereas the intercellular CO₂ concentration (c_i) increased when the two watermelon cultivars were grown under these stresses. The photosynthetic parameters showed greater changes at chilling than at the high temperature, and the CL caused a more pronounced inhibition in PN compared with the CT. After 2 d exposure to the CT, YS01 had higher P_N, g_s, and E, but a lower ci compared with ZJ8424. The maximum efficiency of photosystem (PS) II photochemistry (F_v/F_m), effective quantum yield of PS II photochemistry (Φ_PSII), photochemical quenching (qP), and electron transport rate (ETR) decreased under the CT and CL but showed only a slight drop under the HT. All these stresses significantly increased non-photochemical quenching (NPQ). The CT brought more damage to the photosynthetic apparatus of leaves compared with the CL. In addition, after returning to normal conditions (25/15 °C, 250 μmol m^?2 s^?1) for 3 d, the photosynthetic parameters recovered to pre-stress levels in HT treated seedlings but not in CT treated seedlings. In conclusion, the low irradiance could help to alleviate the extent of photoinhibition of PS II photochemistry caused by chilling and cv. ZJ8424 was more sensitive to the extreme temperatures than cv. YS01.     

Chilling stress and chilling tolerance of sweet potato as sensed by chlorophyll fluorescence

We studied changes in the chlorophyll (Chl) fluorescence components in chilling-stressed sweet potato (Ipomoea batatas L. Lam) cv. Tainung 57 (TN57, chilling-tolerant) and cv. Tainung 66 (TN66, chilling-susceptible). Plants under 12-h photoperiod and 400 μmol m⁻² s⁻¹ irradiance at 24/20 °C (day/night) were treated by a 5-d chilling period at 7/7 °C. Compared to TN66, TN57 exhibited a significantly greater basic Chl fluorescence (F₀), maximum fluorescence (F_m), maximum fluorescence yield during actinic irradiation (F_m′ ), and the quantum efficiency of electron transport through photosystem 2, PS2 (Φ_PS2). Chilling stress resulted in decrease in the potential efficiency of PS2 (F_v/F_m), Φ_PS2, non-photochemical fluorescence quenching (NPQ), non-photochemical quenching (q_N), and the occurrence of chilling injury in TN66. Chilling increased the likelihood of photoinhibition, characterized by a decline in the Chl fluorescence of both cultivars, and photoinhibition during low temperature stress generally occurred more rapidly in TN66.     

Effects of chill stress on prompt and delayed chlorophyll fluorescence from leaves

This paper describes the utilization of a portable solid state device for the simultaneous measurement of prompt and delayed fluorescence transients in leaves from a variety of species subjected to temperature lowering. The induction transients of the two phenomena were not identical as the peak in prompt fluorescence yield always preceded that of delayed fluorescence. Temperature lowering delayed the occurrence of peak fluorescence, increased prompt fluorescence yield, decreased delayed fluorescence yield, and caused the occurrence of a new, more rapid delayed fluorescence transient. Leaves from all species had qualitatively the same type of induction curves although the response to temperature differed between species. The delayed fluorescence yield of chill-sensitive species was reduced to a greater extent than that of chill-insensitive species. Cold hardening leaf material did not greatly change the fluorescence response to temperature lowering. Arrhenius plots showed a linear relationship between delayed fluorescence yield and temperature. There were no breaks that would suggest membrane lipid phase changes. The data indicate that thylakoid membranes of chill-sensitive species are less capable of maintaining a light-induced high energy state at low temperatures than are thylakoid membranes of chill-resistant species.     

Evaluation of chlorophyll fluorescence as a probe for drought stress in willow leaves

The effect of drought on the photosynthetic apparatus of leaves of Salix sp. was studied by measurements of the induction of chlorophyll fluorescence and the capacity for O₂ evolution. Using a multivariate analysis, a model was developed that could predict the degree of drought stress from the data of fluorescence kinetics. Even mild drought stress was detected with high precision; this was not always possible when the photosynthetic capacity was measured. The most clear discrimination between control and drought-stressed leaves was obtained if fluorescence induction was measured at high rather than normal CO₂ levels, and at low rather than high light levels. All information provided by fluorescence pertaining to drought was contained within the slow phase of the induction curve. It is suggested that rapid dehydration is different from drought at the mechanistic level as judged by the fluorescence characteristics.     

Characterization of chilling effects on photosynthetic performance of maize crops during early season growth using chlorophyll fluorescence

Changes in a range of chlorophyll fluorescence parameters weremonitored for leaves of crops of three Zea mays cultivars (MO17,CB3 and LG11) during early canopy development when large fluctuationsin air temperatures occur. Crops were sown on 1 May 1993 andmeasurements made between 17 May and 7 June. Measurements ofthe ratio of variable to maximal fluorescence of dark-adaptedleaves (Fv/Fm) and the quantum efficiency of photosystem IIphotochemistry (     

Use of simultaneous analysis of gas-exchange and chlorophyll fluorescence quenching for analysing the effects of water stress on photosynthesis in apple leaves

Summary A convenient system for the rapid simultaneous measurement of both chlorophyll fluorescence quenching using a modulated light system, and of CO₂, and water vapour exchange by leaves is described. The system was used in a study of the effects of water deficits on the photosynthesis by apple leaves (Malus x domestica Borkh.). Apple leaves were found to have low values of steady-state variable fluorescence, and the existence of significant fluorescence with open traps (F_o) quenching necessitated the measurement and use of a corrected F_o in the calculation of quenching components. Long-term water stress had a marked effect on both gas-exchange and chlorophyll fluorescence quenching. Non-photochemical quenching (qn) in particular was increased in water-stressed leaves, and it was particularly sensitive to incident radiation in such leaves. In contrast, rapid dehydration only affected gas exchange. Relaxation of qn quenching in the dark was slow, taking approximately 10 min for a 50% recovery, in well-watered and in draughted plants, and whether or not the plants had been exposed to high light.     

Sensitivity of the relative Fpl level of chlorophyll fluorescence induction in leaves to the heat stress

The (F_pl-F_o)/F_v value of the fluorescence induction curve is shown to be a more suitable parameter to detect a wider range of heat stress damage to thylakoid membranes as compared to quantities t _1/2 (time of fluorescence rise from F_o to (F_o+F_m)/2 level) and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaacq% aHepaDaaaaaa!39D5!\[\overline \tau \] (the fluorescence induction time defined as the area above the induction curve normalized to F_v=1). A method for exact and automatic F_pl determination is presented.A break point in the quality and behaviour of the fluorescence induction curve of barley leaves incubated at 49°C was reached at the moment (about 240 s) when the transformation of PS II active (Q_B-reducing) to PS II inactive (Q_B-non-reducing) centres was completed. The meaning of the standard F_v and F_v/F_m parameter was then changed.The method of F_pl determination described here may help to increase the analytical value of the standard chlorophyll fluorometers.Abbreviations F_o initial fluorescence - F_m maximal fluorescence - F_pl fluorescence at first inflection point (plateau) - F_v variable fluorescence (F_v=F_m–F_o) - PSM plant stress meter - SD standard deviation     

Characteristics of chlorophyll fluorescence and antioxidative system in super-hybrid rice and its parental cultivars under chilling stress

Characteristics of chlorophyll fluorescence and antioxidative system were investigated in rice (Oryza sativa L.) super-hybrid Liangyoupeijiu (LYPJ), maternal cultivar Peiai64s, and paternal cultivar indica rice 9311 under chilling stress. During 6-d chilling treatment, chlorophyll content of all three genotypes was gradually declined. However, the decrease in photosystem 2 (PS 2) maximum photochemical efficiency (F_v/F_m) and quantum yield of PS 2 (Φ_PS2) was less expressive in LYPJ than in parental cultivars The electrolyte leakage and malondialdehyde content in all cultivars increased after chilling treatment, but LYPJ exhibited the least increasing tendency. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) were higher in LYPJ than in parental cultivars. The results demonstrated that tolerance to chilling stress in LYPJ might be adopted mostly from its maternal cultivar.     

The effect of drought stress on chlorophyll fluorescence in Lolium-Festuca hybrids

The effects of drought on photochemical efficiency of PSII in leaves of 22 hybrids of Festuca pratensis × Lolium multiflorum and Festuca pratensis × Lolium perenne and of Festuca pratensis cv. Skra were investigated. A significant decrease of electron transport efficiency (about 25%) in PSII (Φ_PSII) was not found before 9 days of seedling growth in hydroponics with water potential (Ψ_w) equal to −0.8 MPa (simulated “soil drought”). The decrease of Φ_PSII was similarly related to that of excitation energy capture by open PSII reaction centre (Fv’/Fm’) and also to the decrease of the proportion of oxidized to reduced Q_A (photochemical fluorescence quenching, q_p). According to the drought prolongation, variation of all parameters of fluorescence between genotypes significantly increased. The seedlings of some genotypes were able to recover electron transport efficiency in PSII after increasing water potential in nutrient solution (removing the “soil drought”). When plants grew in containers with soil and 4 genotypes with the highest sensitivity of electron transport to drought (S) as well as 4 genotypes with the highest tolerance (T) were compared 17 days after watering ceased, Ψ_w in leaves considerably decreased, but the differences between S and T genotypes were often not significant in this respect. The differences between S and T genotypes, as values of Fv/Fm were concerned, also appeared small (about 5%), similarly as that of Fv’/Fm’ (5%), q_p (12%) and Φ_PSII (about 15%). Drought stress increased non-photochemical quenching of chlorophyll fluorescence (NPQ) 15 to 47% and this could protect the PSII reaction centres from damages because of energy excess. The increase of NPQ was not closely connected with drought resistance of plants because it was similar in some genotypes tolerant to dehydration as well as in sensitive ones. The results of the experiments suggest that resources of genetic variability in Festulolium may be sufficient for revealing differences between genotypes on the basis of measurement of chlorophyll a fluorescence, as far as their tolerance to soil drought is concerned. As the tolerance of PSII against drought is high, the determinations of fluorescence should be performed rather under severe stress. Such methods seem to be useful for selection of genotypes with high drought tolerance as well as with the ability to at least partial repairing of PSII after drought.     

The effect of sulphite on chlorophyll fluorescence and sucrose metabolism in poplar leaves

Sulphite at concentrations from 0.5 to 5.0 mM was supplied to illuminated, detached poplar (Populus deltoides Bartr. ex Marsh) leaves via the transpiration stream. Chlorophyll a fluorescence parameters, the contents of fructose-2,6-bisphosphate (Fru2,6BP) and starch, and extractable specific activity of sucrose-phosphate synthase (SPS), sucrose synthase (SuSy), acid invertase (AI), neutral invertase (NI), ATP-dependent fructose-6-phosphate 1-phosphotransferase (PFK) and pyrophosphate-dependent fructose-6-phosphate 1-phosphotransferase (PFP) were measured. Chlorophyll fluorescence parameters appeared to be unaffected by sulphite. Application of ≥ 1.0 mM sulphite led to an increase in the content of Fru2,6BP and starch. There was also a decline in the activity of SPS, NI and PFK. On the other hand, the influence of sulphite on the activity of AI and PFP was negligible. Specific activity of SuSy was inhibited by 1.0 and 2.5 mM but activated by 5.0 mM of sulphite. On the basis of the results obtained in the present study, we postulate that sulphite at concentrations ≥ 1.0 mM inhibits primarily sucrose synthesis, favours starch accumulation and has an indirect effect on the sucrolytic activities in poplar leaves.     

Intensity effects on the fluorescence of in vivo chlorophyll

A technique for measuring relative quantum yields of fluorescence with a picosecond streak camera is described. We show that Chlorella pyrenoidosa exhibit an intensity dependent quantum yield when irradiated with single picosecond light pulses. This effect also occurs under conditions that inhibit the activity of the reaction centres, which can therefore be excluded as the cause.When a pulse train (pulse separation 6.9 ns) was used, the quantum yield was further reduced by the light absorbed from previous pulses, which indicates the formation of a quenching species having a relatively long lifetime.Absolute quantum yields calculated from the fluorescence decay show that single excitation pulses of 3 · 10¹³ photons/cm² give results comparable to those obtained by very low intensity methods.     

The arrangement of chloroplasts in cells influences the reabsorption of chlorophyll fluorescence emission. The effect of desiccation on the chlorophyll fluorescence spectra of Rhizomnium punctatum leaves

Chlorophyll fluorescence spectra measured with leaves are distorted by the effect of fluorescence reabsorption. A heterogeneous theoretical model simulating the effect of chloroplast arrangement in a cell on the distortion of chlorophyll fluorescence spectra due to reabsorption was formulated. Desiccation of leaves of the moss Rhizomnium punctatum was carried out as a simple model experiment. The parameters entering the model (maximal number of chloroplasts forming columns in a cell, chloroplast size and chlorophyll concentration in a chloroplast) were estimated by means of light microscopy and spectrophotometry. During the desiccation, a grouping of chloroplasts was observed by light microscopy and the chlorophyll fluorescence emission and excitation spectra of the leaves were measured at room temperature and at 77 K. The leaves were infiltrated with DCMU. The ratio F685/F735 of the main emission bands decreased by about 50% at room temperature and by about 30% at 77 K upon decreasing the leaf water content. No significant changes were found in the ratio E475/E436 of the bands of the leaf fluorescence excitation spectra at 77 K for both 685- and 735-nm emission wavelengths. The excitation spectra and mechanical dilution experiments indicated that no functional changes appeared upon desiccation at the level of energy transfer. Theoretical simulations were in a good agreement with the experimental dependencies. We were able to conclude that the grouping of chloroplasts in cells may enhance the effect of chlorophyll reabsorption and thereby cause a significant decrease of the F685/F735 ratio in the chlorophyll fluorescence spectrum.     

Extended depth-of-focus imaging of chlorophyll fluorescence from intact leaves

Imaging dynamic changes in chlorophyll a fluorescence provides a valuable means with which to examine localised changes in photosynthetic function. Microscope-based systems provide excellent spatial resolution which allows the response of individual cells to be measured. However, such systems have a restricted depth of focus and, as leaves are inherently uneven, only a small proportion of each image at any given focal plane is in focus. In this report we describe the development of algorithms, specifically adapted for imaging chlorophyll fluorescence and photosynthetic function in living plant cells, which allow extended-focus images to be reconstructed from images taken in different focal planes. We describe how these procedures can be used to reconstruct images of chlorophyll fluorescence and calculated photosynthetic parameters, as well as producing a map of leaf topology. The robustness of this procedure is demonstrated using leaves from a number of different plant species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Changes in net photosynthetic rate and chlorophyll fluorescence in potato leaves induced by water stress

Net rates of photosynthesis (PN) saturated by irradiance of >500 mol m-2 s-1 (PAR) significantly decreased in water-stressed potato (Solanum tuberosum L. cv. Kufri Sindhuri) plants. The quantum yield of photochemical energy conversion (Fv/Fm), relative electron transport rate (ETR), and photochemical quenching (Qp) exhibited a parallel decline at high irradiance. A slight decrease in relative water content (RWC) was accompanied by a drastic decline in leaf water potential (w) from -0.2 to -1.0 MPa. Dehydrated leaves showed an increase in the amount of total soluble sugars per unit leaf area which inhibited the photosynthesis in a feedback manner. After rewatering, PN and Fv/Fm were restored to the values of control plants within 24 h, and the restoration was accompanied by a proportionate lowering of content of total soluble sugars in the leaves.     

Effects of prolonged freezing stress on the photosynthetic apparatus of moderately hardy leaves as assayed by chlorophyll fluorescence kinetics

Abstract Moderately frost-hardy leaves of the wintergreen broadleaf woody shrubs Pyracantha coccinea and Ligustrum ovalifolium and the winter annual herb Spinacia oleracea were subjected to extended freezing stress up to 15 d at temperatures 2–8°C above the mean lethal temperature (LT₅₀). After thawing, the fast kinetics of in vivo chlorophyll fluorescence of photosystem II (PSII) and the potential of linear photosynthetic electron transport of isolated thylakoid membranes was measured at room temperature. The lower the minimum freezing temperature and the longer the time of exposure, the greater was the suppression of the fluorescence signals of the leaves and decrease of the electron transport capacity of the thylakoid membranes. The pattern of inactivation of PSII -mediated electron flow, i.e. inhibition of photoreaction to photochemistry and/or electron donation to the photochemical reaction, during long-term freezing at temperatures somewhat above the LT₅₀ of the leaves was similar to that observed earlier after relatively brief exposure of leaves and isolated thylakoid membranes to more severe freezing stress. As injury occurred during freezing in complete darkness, it is likely that prolonged winter stress under natural environmental conditions causes changes in the photosynthetic apparatus of moderately hardy leaves which are not due to photoinhibition.     

Energy-dependent quenching of dark-level chlorophyll fluorescence in intact leaves

A new type of modulation fluorometer was used in the study of energy-dependent chlorophyll fluorescence quenching (q_E) in intact leaves. Under conditions of strong energization of the thylakoid membrane (high light intensity, absence of CO₂) not only variable fluorescence, F_V, but also dark-level fluorescence, F_O, was quenched, leading to definition of a quenching coefficient, q_O. Information on q_O was shown to be essential for correct determination of photochemical (q_Q) and energy dependent quenching (q_E) by the saturation pulse method. The relationship between q_E and q_O was analysed over a range of light intensities at steady state conditions. q_E was found to consist of two components, the second of which is linearly correlated with q_O. q_O and the second component of q_E are interpreted to reflect the state 1 — state 2 shift caused by LHC II phosphorylation.