汽车尾气对四种北方阔叶树叶绿素荧光特性的影响

采用开顶式熏气室研究了汽车尾气对五角槭、山荆子、山梨和茶条槭 4树种叶绿素荧光参数的影响。采用了相同浓度不同处理时间和相同处理时间不同浓度两种方法进行熏气处理。结果表明 ,随着熏气时间的延长和熏气浓度的增加 ,4树种的荧光参数Fv/Fm、Fv/F0 、ΦPSII、qP均逐渐降低 ,qN则逐渐上升。 4树种荧光参数的变化幅度不同 ,其中山荆子变化幅度最大 ,茶条槭的变化幅度最小 ,五角槭和山梨介于两者之间。以叶绿素荧光参数评价 4树种抗污染胁迫能力 ,茶条槭最强 ,五角槭和山梨次之 ,山荆子最弱。     

遮阴对4种紫堇属植物光合特性和叶绿素荧光参数的影响

采用盆栽试验,设置0、20%、40%、60%和80%遮阴度5种遮阴处理,研究遮阴对刻叶紫堇、伏生紫堇、紫堇和黄堇4种紫堇属植物叶绿素含量、光合特性和叶绿素荧光参数的影响,以加快其在园林方面的应用。结果表明: 随着遮阴度的提高,4种植物叶绿素a、叶绿素b和叶绿素(a+b)总量不断增加,刻叶紫堇在80%遮阴处理均达到最大,而伏生紫堇、紫堇和黄堇在60%遮阴处理达到最大;叶绿素a/b、光饱和点、光补偿点和暗呼吸速率的变化趋势呈相反的趋势。4种植物中,刻叶紫堇在80%遮阴处理下,伏生紫堇、紫堇和黄堇在60%遮阴度下各叶绿素荧光参数达到最大。4种植物耐阴性大小为刻叶紫堇＞伏生紫堇＞紫堇＞黄堇。刻叶紫堇在80%遮阴处理,以及伏生紫堇、紫堇和黄堇在60%遮阴处理下光能利用率最大,光合能力最强,最有利于植物的生长。     

Myoplasmic binding of fura-2 investigated by steady-state fluorescence and absorbance measurements.

Binding of the fluorescent Ca2+ indicator dye fura-2 by intracellular constituents has been investigated by steady-state optical measurements. Fura-2's (a) fluorescence intensity, (b) fluorescence emission anisotropy, (c) fluorescence emission spectrum, and (d) absorbance spectra were measured in glass capillary tubes containing solutions of purified myoplasmic proteins; properties b and c were also measured in frog skeletal muscle fibers microinjected with fura-2. The results indicate that more than half, and possibly as much as 85%, of fura-2 molecules in myoplasm are in a protein-bound form, and that the binding changes many properties of the dye. For example, in vitro characterization of the Ca2+-dye reaction indicates that when fura-2 is bound to aldolase (a large and abundant myoplasmic protein), the dissociation constant of the dye for Ca2+ is three- to fourfold larger than that measured in the absence of protein. The problems raised by intracellular binding of fura-2 to cytoplasmic proteins may well apply to cells other than skeletal muscle fibers.     

Plant response to destruxins visualized by imaging of chlorophyll fluorescence

Kinetic fluorescence imaging was used to set a new detection limit for plant exposure to low levels of destruxins – phytotoxins of Alternaria brassicae . A general experimental algorithm is presented that can be used to identify the combination of fluorescence parameters providing the highest contrast between the affected and unaffected plants or plant segments. Leaves of canola ( Brassica napus ) and white mustard ( Sinapis alba ) were exposed to various concentrations of destruxins and images of key fluorescence signals ( F ₀, F _M, F _P, and of F _S) were captured in a single kinetic experiment. Contrast was quantified within these images between the leaf areas exposed to destruxins and the untreated areas. The highest contrast was found in the image constructed by pixel-to-pixel division of images F ₀ by F _P and F ₀ by F _M. Using the F ₀/ F _M ratio image, we were able to detect exposure to destruxin concentration as low as approximately 0.05 mg l⁻¹ applied to canola leaf and approximately 10 mg l⁻¹ when applied to mustard. The detection limits were significantly lower than those obtained by optical microscopy indicating that kinetic chlorophyll fluorescence imaging can be used as a diagnostic tool in screening for varieties with an enhanced resistance to destruxins of Alternaria brassicae .     

Effects of drought on photosynthesis,chlorophyll fluorescence and photoinhibition susceptibility in intact willow leaves

Plants from clonal cuttings of Salix sp. were subjected to a drying cycle of 10 d in a controlled environment. Gas exchange and fluorescence emission were measured on attached leaves. The light-saturated photosynthetic CO₂ uptake became progressively inhibited with decreased leaf water potential both at high, and especially, at low intercellular CO₂ pressure. The maximal quantum yield of CO₂ uptake was more resistant. The inhibition of light-saturated CO₂ uptake at leaf water potentials around-10 bar, measured at a natural ambient CO₂ concentration, was equally attributable to stomatal and non-stomatal factors, but the further inhibition below this water-stress level was caused solely by non-stomatal factors. The kinetics of fluorescence emission was changed at severe water stress; the slow secondary oscillations of the induction curve were attenuated, and this probably indicates perturbations in the carbon reduction cycle. The influence of light level during the drought period was also studied. Provided the leaves were properly light-acclimated, drought at high and low light levels produced essentially the same effects on photosynthesis. However, low-light-acclimated leaves became more susceptible to photoinhibitory treatment under severe water stress, as compared with well-watered conditions.     

Photoinhibition of photosystems I and II using chlorophyll fluorescence measurements

In this study the photoinhibition of photosystems (PS) I and II caused by exposure to high intensity light in oat (Avena sativa, var Prevision) is measured by the emission of chlorophyll fluorescence in intact leaves adapted to darkness. The maximal quantum yield of PS II was lower in plants grown under high light intensity than in plants grown under low intensity, which indicates that PS II is photoinhibited by such conditions. PS I was more stable than PS II in plants exposed to strong light for a moderate time (five photoperiods) since the oxidised plastoquinone pool size under far-red (FR) light was similar in plants grown under high light intensity to plants grown under low intensity, probably as a result of the cyclic electron flow around PS I being stimulated in response to high light intensity. However, over longer times (10 photoperiods) the PS I was photoinhibited, since the oxidised plastoquinone pool size under FR light increased as a consequence of the decrease in PS I activity caused by high light intensity. This practical is intended for advanced students of plant biochemistry and plant physiology.     

土壤镉污染对四种阔叶树苗木叶绿素荧光特性和生长的影响

采用盆栽方法研究了土壤镉污染对白牛槭、刺玫果、金银忍冬和东北山梅花叶绿素荧光参数及生物量的影响.设置0、50、100和200 mg·kg^-1风干土4种镉浓度处理,测定苗木在不同镉浓度土壤中生长70 d后的叶绿素荧光参数.结果表明,随着镉处理浓度的提高,4种树种的F_v/F_m、ΦPSⅡ和qP均逐渐降低,qN则逐渐上升.4种苗木在一个生长季中的生物量累积随着镉浓度的增大逐渐降低.树种间荧光参数和生物量的变化幅度不同,白牛槭的变幅最大.刺玫果最小;以叶绿素荧光参数和生物量评价4树种抗镉污染能力,刺玫果最强、白牛槭最弱.     

Estimating heat tolerance among plant species by two chlorophyll fluorescence parameters

The heat tolerance of 8 temperate- and 1 subtropical-origin C₃ species as well as 17 tropical-origin ones, including C₃, C₄, and CAM species, was estimated using both F₀-T curve and the ratio of chlorophyll fluorescence parameters, prior to and after high temperature treatment. When leaves were heated at the rate of ca. 1 °C min⁻¹ in darkness, the critical temperature (T_c) varied extensively among species. The T_c's of all 8 temperate-origin species ranged between 40–46 °C in winter (mean temperature 16–19 °C), and between 32–48 °C in summer (mean temperature ca. 30 °C). Those for 1 subtropical- and 12 tropical-origin C₃ species ranged between 25–44 °C and 35–48 °C, and for 1 CAM and 4 C₄ species were 41–47 and 45–46 °C, respectively. Acclimating three C₃ herbaceous plants at high temperature (33/28 °C, day/night) for 10 d in winter caused their T_c's rising to nearly the values measured in summer. When leaves were exposed to 45 °C for 20 min and then kept at room temperature in darkness for 1 h, a significant correlation between RF_v/m (the ratio of F_v/F_m before and after 45 °C treatment) and T_c was observed for all tested temperate-origin C₃ species as well as tropical-origin CAM and C₄ species. However, F₀ and F_v/F_m of the tropical-origin C₃ species were less sensitive to 45 °C treatment, regardless of a large variation of T_c; thus no significant correlation was found between their RF_v/m and T_c. Thus T_c might not be a suitable index of heat tolerance for plants with wide range of environmental adaptation. Nevertheless, T_c's of tropical origin C₃ species, varying and showing high plasticity to seasonal changes and temperature treatment, appeared suitable for the estimation of the degree of temperature acclimation in the same species.     

Use of chlorophyll fluorescence to estimate the effect of photoinhibition in outdoor cultures ofSpirulina platensis

Chlorophyll fluorescence measurements were used to evaluate the effect of temperature on photoinhibition inSpirulina platensis cultures grown in tubular reactors outdoors. Cultures grown at 35 °C during the day time showed a lower reduction in the Fv/Fm ratio as compared to cultures grown at 25 °C. It is demonstrated that the lower temperature photoinhibited cells can undergo a complete recovery once transferred to low light and higher temperature. This recovery does not take place when 100 µg ml^-1 chloramphenicol is added to cells. The recovery is light dependent and cells incubated in the dark at low temperature do not show a recovery in the Fv/Fm ratio. The data presented strongly support the hypothesis that photoinhibition takes place in outdoorSpirulina cultures. At the same time it is demonstrated that fluorescence measurements can be used as a fast reliable indication for photoinhibition in outdoor algal cultures.Author for correspondencePublication No. 69 of the Microalgal Biotechnology Laboratory.     

The characterization of photoinhibition and recovery during cold acclimation in Arabidopsis thaliana using chlorophyll fluorescence imaging

The responses to photoinhibition of photosynthesis at low temperature and subsequent recovery were examined in Arabidopsis thaliana (ecotype Columbia) developed at 4°C cold-acclimating conditions, 23°C non-acclimating conditions and for non-acclimated plants shifted to 4°C (cold-shifted). These responses were determined in planta using Chl fluorescence imaging. We show that cold acclimation results in an increased tolerance to photoinhibition in comparison with non-acclimated plants and that growth and development at low temperature is essential for this to occur. Cold-shifted plants were not as tolerant as the cold-acclimated plants. In addition, we demonstrate this tolerance is as a result of growth under high PSII excitation pressure, that can be modulated by growth temperature or growth irradiance. Cold-acclimated and cold-shifted plants fully recover from photoinhibition in the dark, whereas non-acclimated plants show reduced levels of recovery and demonstrate a requirement for light. The role of the PSII repair cycle, PSII quenching centres, and the use of Chl fluorescence imaging to monitor photoinhibitory responses in planta are discussed.     

Assessment of the frost sensitivity of Trifolium species by chlorophyll fluorescence analysis

The potential of the chlorophyll fluorescence technique in screening for frost sensitivity in a range of Trifolium species from different geographical origins was assessed by measuring the decrease in variable chlorophyll fluorescence (F_var) of leaves after freezing at - 5°C for 60 min. The method was rapid and the results obtained agreed well with a visual assessment of freezing injury carried out after leaves were returned to optimal growth conditions for 72 h. Trifolium alexandrinum (Berseem clover) cv. Tabor originating from Israel was shown to be the most frost sensitive species studied and Trifolium subterraneum (subterranean clover) cv. Mt. Barker, from temperate regions of Australia, the most frost resistant. On extended periods of freezing, frost damage increased and this was associated with a further reduction in variable chlorophyll fluorescence and in quenching capacity of the thylakoid membranes. These results thus indicate that substantial thylakoid membrane dysfunction is induced at freezing temperatures. Furthermore, it was found that frost hardening of the frost sensitive species T. alexandrinum for 21 days at 5°C reduced the extent of damage sustained by the thylakoid membranes as shown by higher fluorescence quenching capacity, smaller reduction in variable fluorescence (F_var) and higher initial fluorescence (F_o) when leaves of hardened plants were frozen at -5°C and -7°C.     

The size of the population of weakly coupled chlorophyll pigments involved in thylakoid photoinhibition determined by steady-state fluorescence spectroscopy

On the basis of experiments with singlet quenchers and in agreement with previous data, it is suggested that a population of energetically weakly coupled chlorophylls may play a central role in photoinhibition in vivo and in vitro. In the present study, we have used steady state fluorescence techniques to gain direct evidence for these uncoupled chlorophylls. Due to the presence of their emission maxima, near 650 nm and more prominently in the 670--675 nm interval both chlorophylls b and a seem to be involved. A straightforward mathematical model is developed to describe the data which allows us to conclude that the uncoupled/weakly coupled population size is in the range of 1--3 molecules per photosystem.     

The size of the population of weakly coupled chlorophyll pigments involved in thylakoid photoinhibition determined by steady-state fluorescence spectroscopy

On the basis of experiments with singlet quenchers and in agreement with previous data, it is suggested that a population of energetically weakly coupled chlorophylls may play a central role in photoinhibition in vivo and in vitro. In the present study, we have used steady state fluorescence techniques to gain direct evidence for these uncoupled chlorophylls. Due to the presence of their emission maxima, near 650 nm and more prominently in the 670-675 nm interval both chlorophylls b and a seem to be involved. A straightforward mathematical model is developed to describe the data which allows us to conclude that the uncoupled/weakly coupled population size is in the range of 1-3 molecules per photosystem.     

ΔpH-dependent chlorophyll fluorescence quenching indicating a mechanism of protection against photoinhibition of chloroplasts

Intact isolated spinach chloroplasts were subjected to photoinhibitory conditions (high light and lack of CO₂). Photoinhibition of the electron transport system was considerably diminished when the chloroplasts were in a low-fluorescent state related to a high proton gradient across the thylakoid membranes, as compared to a high-fluorescent state in which ΔpH-dependent fluorescence quenching was abolished by addition of uncouplers. The hypothesis is discussed that in chloroplasts exposed to excess light, photoinhibition is partly prevented by increased thermal dissipation of excitation energy, as expressed by ΔpH-dependent (‘energy-dependent’) chlorophyll a fluorescence quenching.     

CO2 photoassimilation and chlorophyll fluorescence in two clover species showing different response to O3

The current study evaluated photosynthetic processes in two clover species based on their performance under high O₃ conditions (150 nl l^–1 for 3 h). These species are Trifolium repens L. and Trifolium pratense L., which are well known for their different sensitivity to ozone. Ozone affected the two clover species very differently. In T. pratense, ozone induced visible symptoms of damage even though CO₂ photoassimilation, stomatal conductance and the electron transport rate were not affected. A decrease in the optimal quantum yield was observed in T. pratense immediately after the end of the period of O₃ stress but it reverted to a value similar to the control 24 h after removing the stress, indicating that non-irreversible photoinhibition had occurred. Data obtained for symptomatic T. pratense indicate that still-green living tissue of the leaf is able to carry out CO₂ assimilation; the only parameter found to be affected by O₃ was the efficiency of excitation capture. In T. repens, acute O₃ fumigation induced inhibition of photosynthetic activity, enhanced stomatal closure and increased the reduction state of the PSII primary acceptor. A possible explanation for the inhibition of photosynthesis could reside in inhibition of the Calvin cycle over-reducing PSII, thus increasing (1 – q_P) and increasing non-photochemical quenching.     

Probing corticular photosynthesis through in vivo chlorophyll fluorescence measurements: evidence that high internal CO levels suppress electron flow and increase the risk of photoinhibition

Twigs of many woody plants possess chlorenchyma under a well-developed periderm which lacks stomata and impedes both gas diffusion and light penetration. The so-called corticular photosynthesis, occurring in the shade and under extremely high CO(2) concentrations, was probed in this study through in vivo chlorophyll fluorescence measurements. Field comparisons between twigs and corresponding leaves in five species indicated that both the dark- and light-adapted PSII photochemical efficiencies are considerably lower in twigs at all incident photon fluence rates, in spite of the significant attenuation of solar radiation by the periderm. Light saturation curves for linear electron transport rates (corrected according to the actual light intensities reaching twig chlorenchyma) were compatible with a shade-acclimated photosynthetic machinery, showing very low maximum electron transport rates (at approximately 5% of the corresponding leaf values) and threshold irradiances for light saturation. However, removing periderms from twig segments (i.e. relieving the twig interior form the high CO(2) partial pressures) considerably improved the light-adapted (but not the dark-adapted) PSII photochemical efficiency, allowing the assumption that the high internal CO(2) levels may interfere with the smooth functioning of photosynthesis. Indeed, laboratory experiments with twig segments equilibrated under various CO(2) levels (0.036-20%), resulted in a progressive decrease of light-adapted PSII photochemical yield, with the values obtained at 20% CO(2) being similar to those obtained with intact twigs in the field. Further experiments indicated that high CO(2) combined with high light suppressed the development of a photoprotective non-photochemical quenching through a reduction of its fast relaxing component, accompanied by a higher risk of photoinhibition. It is suggested that high internal CO(2) concentrations in twigs impede photosynthesis possibly through acidification of protoplasm and impairment of the pH-dependent high energy state quenching followed by reduction in the efficiency of heat dissipation.     

A study on the energy-dependent quenching of chlorophyll fluorescence by means of photoacoustic measurements

The mechanism of energy-dependent quenching (q_E) of chlorophyll fluorescence was studied employing photoacoustic measurements of oxygen evolution and heat release. It is shown that concomitant to the formation of q_E the yield of open reaction centers _p decreases indicating that q_E quenching originates from a process being competitive to fluorescence as well as to photochemistry. The analysis of heat release (rate of thermal deactivation) shows: 1. The competitive process is not given by a still unknown energy storing process. 2. If the competitive process would be a futile cycle the life-times of the involved intermediates had to be faster than 50 s.The results of the photoacoustic measurements are in line with the idea that q_E quenching originates from an increased probability of thermal deactivation of excited chlorophylls.Abbreviations F actual fluorescence - F_m fluorescence yield with all PS II reaction centers closed in a light adapted state - F₀ fluorescence yield with all PS II reaction centers open in a light adapted state - PS Photosystem - _p intrinsic photochemical yield - q_E energy-dependent quenching - q_I photoinhibition quenching - q_N non-photochemical quenching - q_P photochemical quenching - q_T state transition quenching     

Whole-genome analysis of giraffe supports four distinct species

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The response of seedlings of two dipterocarp species to nutrient additions and ectomycorrhizal infection

An experiment was conducted to investigate the effect of ectomycorrhizal infection on growth and nutrient uptake, especially of P and K of dipterocarp seedlings.Hopea helferi (Dyer) Blanco andHopea odorata Roxb. seedlings were grown in a sandy loam soil given a basal dressing. Nutrient treatments were unamended soil (NIL), amended soil with the addition of P and K (F), amended soil without P but with K (-P), amended soil without K but with P (-K), amended soil without P or K addition (-PK). Seedlings grown in the amended soil treatments showed foliar symptoms suggestive of calcium deficiency. Ectomycorrhizal infection appeared to improve shoot Ca concentration and relieved the foliar symptoms. Ectomycorrhizal infection inH. odorata plants increased shoot P concentration and increased shoot and total dry weight to the same or greater extent than those of uninfected plants growing on P amended soil.H. helferi showed a positive response to ectomycorrhizal infection in shoot, root and total dry weight in all nutrient treatments but no response to the nutrient treatments themselves.