共查询到20条相似文献,搜索用时 31 毫秒
1.
Jelte Rozema Peter Boelen Bjørn Solheim Matthias Zielke Alwin Buskens Marieke Doorenbosch Ruben Fijn Jelger Herder Terry Callaghan Lars Olof Björn Dylan Gwynn Jones Rob Broekman Peter Blokker Willem van de Poll 《Plant Ecology》2006,182(1-2):121-135
The response of tundra plants to enhanced UV-B radiation simulating 15 and 30% ozone depletion was studied at two high arctic
sites (Isdammen and Adventdalen, 78° N, Svalbard).The set-up of the UV-B supplementation systems is described, consisting
of large and small UV lamp arrays, installed in 1996 and 2002. After 7 years of exposure to enhanced UV-B radiation, plant
cover, density, morphological (leaf fresh and dry weight, leaf thickness, leaf area, reproductive and ecophysiological parameters
leaf UV-B absorbance, leaf phenolic content, leaf water content) were not affected by enhanced UV-B radiation. DNA damage
in the leaves was not increased with enhanced UV-B in Salix polaris and Cassiope tetragona. DNA damage in Salix polaris leaves was higher than in leaves of C. tetragona. The length of male gametophyte moss plants of Polytrichum hyperboreum was reduced with elevated UV-B as well as the number of Pedicularis hirsuta plants per plot, but the inflorescence length of Bistorta vivipara was not significantly affected. We discuss the possible causes of tolerance of tundra plants to UV-B (absence of response
to enhanced UV-B) in terms of methodology (supplementation versus exclusion), ecophysiological adaptations to UV-B and the
biogeographical history of polar plants 相似文献
2.
We report a long-term experiment on the photosynthetic response of natural vegetation of Deschampsia antarctica (Poaceae) and Turgidosculum complicatulum (Lichenes) to altered UV-B levels on Léonie Island, Antarctica.UV-B above the vegetation was reduced by filter screens during two seasons. Half of the screens were transparent to UV-A and UV-B (ambient treatment) or absorbing UV-B and part of the UV-A (below-ambient treatment). Half of the wedge- shaped filters had side walls leading to an enhancement of the daily mean temperature in summer by 2–4 °C, simulating rising mean air temperature on the Antarctic Peninsula. The other half of the filters were without side walls resulting in close-to-ambient temperature underneath. Plots without filters served as controls.UV-B supplementation of an extra 1.3 kJ UV-BBE was achieved using UV-mini-lamp systems during 15 days in the second season.We found no evidence that altered incident UV-B levels and temperature had an effect on maximum photosystem II efficiency (F
v/F
m) and effective photosystem II efficiency (F/F
m) in both species. UV-B reduction did not influence contents of chlorophyll, carotenoids and methanol-soluble UV absorbing compounds in D. antarctica.Flowering shoot length of D. antarctica was not affected by UV-B reduction. Temperature enhancement tended to result in longer inflorescence axes. Results of two austral summer seasons of UV- reduction in natural stands of D. antarctica and T. complicatulum suggest that current ambient levels of UV-B do not have a direct effect on the photosynthetic performance and pigment contents of these species. Cumulative effects on growth have not been recorded after two years but can not be excluded on a longer term. 相似文献
3.
After preheating of Amaranthus chloroplasts at elevated temperatures (up to 45°C), the chlorophyll a fluorescence level under low excitation light rises as compared to control (unheated) as observed earlier in other chloroplasts (Schreiber U and Armond PA (1978) Biochim Biophys Acta 502: 138–151). This elevation of heat induced fluorescence yield is quenched by addition of 0.1 mM potassium ferricyanide, suggesting that with mild heat stress the primary electron acceptor of photosystem II is more easily reduced than the unheated samples. Furthermore, the level of fluorescence attained after illumination of dithionite-treated samples is independent of preheating (up to 45°C). Thus, these experiments indicate that the heat induced rise of fluorescence level at low light can not be due to changes in the elevation in the true constant F0 level, that must by definition, be independent of the concentration of QA. It is supposed that the increase in the fluorescence level by weak modulated light is either partly associated with dark reduction of QA due to exposure of chloroplasts to elevated temperature or due to temperature induced fluorescence rise in the so called inactive photosystem II centre where QA are not connected to plastoquinone pool. In the presence of dichlorophenyldimethylurea the fluorescence level triggered by weak modulated light increases at alkaline pH, both in control and heat stressed chloroplasts. This result suggests that the alkaline pH accelerates electron donation from secondary electron donor of photosystem II to QA both in control and heat stressed samples. Thus the increase in fluorescence level probed by weak modulated light due to preheating is not solely linked to increase in true F0 level, but largely associated with the shift in the redox state of QA, the primary stable electron acceptor of photosystem II.Abbreviations ADRY
Acceleration of Deactivation of Reaction of Enzyme Y
- CCCP
Carbonyl cyanide 4-(trifluoromethoxy)-phenylhydrazone
- Chl
Chlorophyll
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- FeCN
potassium ferricyanide
- HEPES
4-(2-hydroxy ethyl)-1-piperazine ethane sulfonic acid
- LHCP
Light harvesting chlorophyll protein
- MES
(4-morpholine ethane sulfonic acid)
- PS
photosystem
- QA and QB
first and second consecutive electron acceptors of photosystem II
- TES
(2-[tris(hydroxymethyl)-methylamino]-1-ethanesulfonic acid) sulfonic acid
- TRICINE
N-[tris(hydroxymethyl)methyl] glycine 相似文献
4.
Yuichi Takeuchi Reiko Fukumoto Hirokazu Kasahara Takeshi Sakaki Mitsutoshi Kitao 《Plant cell reports》1995,14(9):566-570
Cotyledons excised from dark-grown seedlings of cucumber (Cucumis sativus L.) were cultured in vitro under UV radiation at different wavelengths, obtained by passage of light through cut-off filters with different transmittance properties. Growth and the synthesis of chlorophyll (Chl) in cotyledons were inhibited and malondialdehyde was accumulated upon irradiation at wavelengths below 320 nm. Exogenous application of scavengers of free radicals reversed the growth inhibition induced by UV-B. Measurement of the fluorescence of Chl a suggested that electron transfer in photosystems was affected by UV-B irradiation. On the basis of these results, the involvement is postulated of active species of oxygen in damages to thylakoid membranes and the growth inhibition that are induced by UV-B irradiation.Abbreviations Chl
chlorophyll
- Fm
maximal fluorescence (dark)
- Fm
maximal fluorescence (light)
- Fv
variable fluorescence (dark)
- Fv
variable fluorescence (light)
- MDA
malondialdehyde
- O2
Superoxide radical
- PS
photosystem
- qN
non-photochemical quenching of fluorescence
- qP
photochemical quenching of fluorescence
- UV-BBE
biologically effective UV-B radiation
- WL(T = 0.5)
wavelength at which 50% transmittance occurs 相似文献
5.
UV-B exposure enhances senescence of wheat leaves: modulation by photosynthetically active radiation
Pradhan MK Joshi PN Nair JS Ramaswamy NK Iyer RK Biswal B Biswal UC 《Radiation and environmental biophysics》2006,45(3):221-229
The alterations in structure and function of photosystem II (PS II) during the senescence of primary leaves of wheat seedlings have been compared with the changes induced by ultraviolet-B (UV-B) radiation in the presence or absence of photosynthetically active radiation (PAR). The results indicated that the senescence-induced loss in pigment content, thylakoid membrane integrity and carotenoid-to-chlorophyll (Car-to-Chl) energy transfer efficiency was intensified by exposure to UV-B radiation. Different parameters for the measurement of PS II activity, such as Chl a fluorescence, O2-evolution and thermoluminescence intensity, were altered during senescence and these alterations were furthered by UV-B irradiation. The damage of photosynthetic apparatus by UV-B exposure in the presence of PAR was less than the damage in absence of PAR. The activation of molecular defense mechanisms could be a factor in the alleviation of UV-B damage in the presence of PAR. 相似文献
6.
The fluorescence kinetics of both intact needles and isolated chloroplasts of summer active and winter stressed Pinus sylvestris were measured at both room temperature and 77 K. It was confirmed that winter stress inhibited the photochemical capacity of photosystem II but also that winter stress caused the strongest inhibition of the electron transport at the site where the plastoquinone pool is reduced. Parallel analyses of the fluorescence characteristics of photosystem II (F693) and photosystem I (F729) during photosystem II trap closure furthermore revealed that the yield of spillover of excitation energy from photosystem II to photosystem I decreased upon winter stress. We suggest that this is because of an increased radiationless decay of excitation energy both at the reaction center and antennae levels of photosystem II. There is, however, also a possibility that the decreased yield of spill-over is accentuated by a partial detachment of the light harvesting chlorophyll a/b complex from photosystem II upon winter stress.Paper presented at the FESPP meeting in Strasbourg (1984). 相似文献
7.
In order to understand the mechanism of photodamage induced by solar radiation under natural conditions, we studied the interaction
of visible and ultraviolet-B light in the inactivation and repair of the Photosystem II complex by using oxygen evolution
and flash-induced chlorophyll fluorescence measurements. In isolated spinach thylakoids and Synechocystis 6803 cells, in which de novo protein synthesis is blocked by lincomycin, photodamage of Photosystem II by visible and UV-B light is characterized by linear
semilogarithmic inactivation curves for both separate and combined illumination protocols. The extent of PS II inactivation
obtained after combined illumination can be well simulated by assuming independent damaging events induced by visible and
UV-B photons. In intact Synechocystis cells capable of protein repair, simultaneous illumination by visible and UV-B light impairs Photosystem II activity to a
smaller extent than expected from the independent damaging events. This protective effect is pronounced at low visible light
(130 μE m−2 s−1), but becomes negligible at high intensities (1300 μE m−2 s−1). Exposure of intact Synechocystis 6803 cells to direct sunlight leads to a rapid inactivation of PS II, accompanied by the accumulation of donor side inhibited
centers. This phenomenon, which shows the impairment of the manganese cluster of water oxidation was not observed when the
ultraviolet components of sunlight were filtered out. We conclude that visible and UV-B photons inactivate PS II via non-interacting
mechanisms, which affect different target sites. In intact cells, the two spectral regions do interact, and results in synergistically
enhanced protein repair capacity when UV-B radiation is accompanied by low intensity visible light, which provides protection
against photodamage. However, this ameliorating effect becomes insignificant at high light intensities characteristic of direct
sunlight.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Seedlings of two Mediterranean plants, the slow-growing, evergreen sclerophyll Ceratonia siliqua L. and the fast growing drought semi-deciduous Phlomis fruticosa L., were grown for one year in the field at ambient or ambient plus supplemental UV-B radiation (equivalent to a 15% ozone depletion) and two levels of applied fertilizers (NPK). The effects on growth, morphological, anatomical and physiological parameters were measured at final plant harvest. Additional nutrients increased leaf nitrogen, improved growth and reduced the root/shoot ratio in both plants, yet these effects were more pronounced in the fast growing P. fruticosa. A nutrient-induced increase in chlorophyll content was also observed in this plant. The growth responses to UV-B radiation were different for the two species. Growth in C. siliqua was not affected by UV-B radiation at both nutrient levels and the same was true for P. fruticosa at low nutrients. However, at the high nutrient level, supplemental UV-B radiation improved growth in P. fruticosa, indicating a strong interaction between the treatments. Photosystem II (PSII) photochemical efficiency, methanol-extractable UV-B absorbing capacity, total phenolics and tannins were not affected by either treatment in both plants. It is concluded that nutrient levels can strongly modify the UV-B radiation effects on growth of P. fruticosa. We presume that this may be correlated to the fast growing habit of this species. 相似文献
9.
Inhibition of photosynthesis by UV-B was investigated in the thalloid liverwort Conocephalum conicum Dum. UV-B irradiance was adjusted to a strength producing 50% inhibition of the rate of photosynthesis during 10 min of irradiation. A linear relationship of the fluorescence terms Fv/Fm of photosystem (PS) II and JP was observed following a UV-B irradiation. This suggested that PS II was a major site of UV-B-induced damage of photosynthesis. The apparent inhibition of Fv/Fm was much smaller when electron flow to the secondary PS II acceptor QB was inhibited by DCMU or when Fv/Fm was measured at 77 K. Apparently, the major target of UV-B effects was electron donation to the PS II reaction center, rather than electron transfer reactions at the PS II acceptor side. The time required for repair of PS II from UV-B-induced damage was light-dependent and minimal at a flux density of 5 μE m?2 s?1. Low temperatures and the presence of streptomycin inhibited the repair processes of PS II, indicating that protein synthesis may be involved in the recovery of PS II. The data indicate that UV-B irradiation on bright and cool winter days may be most harmful for photosynthesis of C. conicum. A repeated irradiation of the thalli with UV-B induced tolerance of photosynthesis which was related to an accumulation of pigments with a maximum of absorption around 315 nm. 相似文献
10.
Influence of Temperature on the Effects of Artificially Enhanced UV-B Radiation on Aquatic Bryophytes Under Laboratory Conditions 总被引:2,自引:1,他引:1
Núñez-Olivera E. Martínez-Abaigar J. Tomás R. Beaucourt N. Arróniz-Crespo M. 《Photosynthetica》2004,42(2):201-212
We examined, under laboratory conditions, the influence of temperature (2 °C vs. 10 °C) on the physiological responses of two aquatic bryophytes from a mountain stream to artificially enhanced UV-B radiation for 82 d. These organisms may be exposed naturally to relatively low temperatures and high levels of UV-B radiation, and this combination is believed to increase the adverse effects of UV-B radiation. In the moss Fontinalis antipyretica, UV-B-treated samples showed severe physiological damages, including significant decreases in chlorophyll (Chl) and carotenoid (Car) contents, Chl a/b and Chl/phaeopigment ratios, Chl a fluorescence parameters Fv/Fm and PS2, electron transport rate (ETRmax), and growth. In the liverwort Jungermannia cordifolia, UV-B radiation hardly caused any physiological change except for growth reduction. Thus, this liverwort seemed to be more tolerant to UV-B radiation than the moss under the specific experimental conditions used, maybe partly due to the accumulation of UV-B absorbing compounds. The influence of temperature on the effects of UV-B radiation depended on the species: the higher the UV-B tolerance, the lower the influence of temperature. Also, different physiological variables showed varied responses to this influence. Particularly, the lower temperature used in our study enhanced the adverse effects of UV-B radiation on important physiological variables such as Fv/Fm, growth, and Chl/phaeopigment ratios in the UV-B-sensitive F. antipyretica, but not in the more UV-B-tolerant J. cordifolia. Thus, the adverse effects of cold and UV-B radiation were apparently additive in the moss, but this additiveness was lacking in the liverwort. The Principal Components Analyses (PCA) conducted for both species with the physiological data obtained after 36 and 82 d of culture confirmed the above results. Under natural conditions, the relatively high water temperatures in summer might facilitate the acclimation of aquatic bryophytes from mountain streams to high levels of UV-B radiation. This may be relevant to predict the consequences of concomitant global warming and increasing UV-B radiation. 相似文献
11.
The effects of UV-B radiation (290–320 nm) on development of damping-off of spinach (Spinacia oleracea) caused by the fungusFusarium oxysporum were examined in a growth cabinet. The incidence of disease greatly increased when experimental plants were grown in visible
radiation with supplementary UV-B radiation. This increase was suppressed by increasing the irradiation of visible radiation.Fusarium oxysporum was isolated from the roots of all damping-off plants and the roots of some unwilted plants, indicating that spinach infected
with the pathogen did not necessarily suffer from damping-off in 15d. Supplementary UV-B radiation suppressed the increase
in growth components such as the number of leaves, the plant height and the fresh weight of aboveground plant parts, but did
not affect the fresh weight of roots. The ratio of the number of plants infected with pathogen to the total number of plants
was over 80% irrespective of light conditions. It was suggested that the defense response of spinach to this pathogen was
greatly influenced by the physiological state of aboveground plant parts resulting from supplementary UV-B radiation. 相似文献
12.
We measured the responses of pigments and chlorophyll a fluorescence parameters of the Antarctic leafy liverwort Cephaloziella varians to snowmelt during austral spring 2005 at Rothera Point on the western Antarctic Peninsula. Although no changes to the concentrations
of UV-B photoprotective pigments were detected during snowmelt, chlorophyll and carotenoid concentrations and maximum photosystem
(PS)II yield (F
v
/F
m) were respectively 88, 60 and 144% higher in the tissues of the liverwort that had recently emerged from snow than in those
under a 10 cm depth of snow. A laboratory experiment similarly showed that effective PSII yield increased rapidly within the
first 45 min after plants sampled from under snow were removed to an illuminated growth cabinet. The pigmentation and PSII
yields of plants during snowmelt were also compared with those of plants in January, during the middle of the growing season
at Rothera Point. During snowmelt, plants had lower F
v
/F
m values, chlorophyll a/b ratios and concentrations of UV-B photoprotective pigments and carotenoids than during mid-season, suggesting that although
there is some recovery of PSII activity and increases in concentrations of photosynthetic pigments during snowmelt, the metabolism
of C. varians is restricted during this period. 相似文献
13.
Eosin, a known generator of singlet oxygen, applied to leaf discs of Pisum sativum L. sensitized the inhibition of photosynthesis. Analysis of partial photosynthetic electron-transport reactions and of the kinetics of variable chlorophyll fluorescence located the damage at photosystem II. This injury required the presence of oxygen and was also caused by the irradiation of eosin-treated leaf tissue with green light. The role of oxygen and photodynamic reactions in the susceptibility of photosystem II to damage by environmental stresses is discussed.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DCPIP
2,6-dichlorophenolindophenol
- DPC
1,5-diphenylcarbazide
- PSI
photosystem I
- PSII
photosystem II
-
1O2
singlet oxygen
- Tricine
N-[2-hydroxyl-3,1-bis(hydroxymethyl)ethyl]-glycine 相似文献
14.
In the cyanobacterium Anabaena variabilis the dependence of photoinhibition on fluence rate, duration and wavelength of irradiation were studied by measurements of oxygen production and fluorescence emission spectra. The analysis of the photosynthetic activity revealed that photoinhibition affects exclusively photosystem II (PS II), whereas photosystem I (PS I) remained largely unimpaired. Furthermore, PS II fluorescence emission decreased much faster in bleached than in unbleached controls.Studying the wavelength dependence of photoinhibition it was found that only radiation between 520 and 680 nm causes photoinhibition. This is about the same range of wavelengths which causes photobleaching. Fluorescence emission spectra of samples exposed to high fluence rates of 582 and 662 nm, respectively, essentially agree with those samples exposed to high fluence rates of white light, whereas the fluorescence emission spectra of samples exposed to blue light resemble those exposed to dim white light.NaN3, a substance which prevents photobleaching, inhibits the photosynthetic O2 production of Anabaena and, hence, enhances the photoinhibitory effect. 相似文献
15.
Bean (Phaseolus vulgaris L. cv. Berbukskaya) seedlings were pre-treated with choline compounds, 19 mM 2-ethyltrimethylammonium chloride (Ch) or 1.6 mM 2-chloroethyltrimethylammonium chloride (CCh), during 24 h, then after 6 d the excised primary leaves were exposed to UV-B and high temperature stress. Chlorophyll (Chl) fluorescence, delayed light emission, accumulation of photosynthetic pigments, contents of thiobarbituric acid reactive substances, and activities of the active oxygen detoxifying enzymes (superoxide dismutase, ascorbate peroxidase, and glutathione reductase) were examined. Pre-treatment of plants with Ch or CCh enhanced the resistance of photosystem 2 (PS2) photochemistry to UV-B and heat injuries. The higher stress resistance can be explained by the increased activity of the detoxifying enzymes. The increased content of UV-B-absorbing pigments may also contribute to the enhanced resistance of choline-treated plants to UV-B radiation. 相似文献
16.
Yuichiro Takahashi Hideki Matsumoto Michel Goldschmidt-Clermont Jean-David Rochaix 《Plant molecular biology》1994,24(5):779-788
Using particle gun-mediated chloroplast transformation we have disrupted the psbK gene of Chlamydomonas reihardtii with an aadA expression cassette that confers resistance to spectinomycin. The transformants are unable to grow photoautotrophically, but they grow normally in acetate-containing medium. They are deficient in photosystem II activity as measured by fluorescence transients and O2 evolution and they accumulate less than 10% of wild-type levels of photosystem II as measured by immunochemical means. Pulse-labeling experiments indicate that the photosystem II complex is synthesized normally in the transformants. These results differ from those obtained previously with similar cyanobacterial psbK mutants that were still capable of photoautotrophic growth (Ikeuchi et al., J. Biol. Chem. 266 (1991) 1111–1115). In C. reinhardtii the psbK product is required for the stable assembly and/or stability of the photosystem II complex and essential for photoautotrophic growth. The data also suggest that the stability requirements of the photosynthetic complexes differ considerably between C. reinhardtii and cyanobacteria. 相似文献
17.
Summary Irradiation of the principal photosystem II light-harvesting chlorophyll-protein antenna complex, LHC II, with high light intensities brings about a pronounced quenching of the chlorophyll fluorescence. Illumination of isolated thylakoids with high light intensities generates the formation of quenching centres within LHC II in vivo, as demonstrated by fluorescence excitation spectroscopy. In the isolated complex it is demonstrated that the light-induced fluorescence quenching: a) shows a partial, biphasic reversibility in the dark; b) is approximately proportional to the light intensity; c) is almost independent of temperature in the range 0–30°C; d) is substantially insensitive to protein modifying reagents and treatments; e) occurs in the absence of oxygen. A possible physiological importance of the phenomenon is discussed in terms of a mechanism capable of dissipating excess excitation energy within the photosystem II antenna.Abbreviations chla
chlorophyll a
- chlb
chlorophyll b
- F0
fluorescence yield with reaction centers open
- Fm
fluorescence yield with reaction centres closed
- Fi
fluorescence at the plateau level of the fast induction phase
- LHC II
light-harvesting chlorophyll a/b protein complex II
- PS II
photosystem II
- PSI
photosystem I
- Tricine
N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine 相似文献
18.
Evaluation of the role of damage to photosystem II in the inhibition of CO2 assimilation in pea leaves on exposure to UV-B radiation 总被引:1,自引:1,他引:0
Mature pea (Pisum sativum L., cv. Meteor) leaves were exposed to two levels of UV-B radiation, with and without supplementary UV-C radiation, during 15 h photoperiods. Simultaneous measurements of CO2 assimilation and modulated chlorophyll fluorescence parameters demonstrated that irradiation with UV-B resulted in decreases in CO2 assimilation that are not accompanied by decreases in the maximum quantum efficiency of photosystem II (PSII) primary photochemistry. Increased exposure to UV-B resulted in a further loss of CO2 assimilation and decreases in the maximum quantum efficiency of PSII primary photochemistry, which were accompanied by a loss of the capacity of thylakoids isolated from the leaves to bind atrazine, thus demonstrating that photodamage to PSII reaction centres had occurred. Addition of UV-C to the UV-B treatments increased markedly the rate of inhibition of photosynthesis, but the relationships between CO2 assimilation and PSII characteristics remained the same, indicating that UV-B and UV-C inhibit leaf photosynthesis by a similar mechanism. It is concluded that PSII is not the primary target site involved in the onset of the inhibition of photosynthesis in pea leaves induced by irradiation with UV-B. 相似文献
19.
Growth under UV-B radiation increases tolerance to high-light stress in pea and bean plants 总被引:1,自引:0,他引:1
Bolink Esther M. van Schalkwijk Ilse Posthumus Freek van Hasselt Philip R. 《Plant Ecology》2001,154(1-2):147-156
Pea (Pisum sativum L.) and bean (Phaseolus vulgaris L.) plants were exposed to enhanced levels of UV-B radiation in a growth chamber. Leaf discs of UV-B treated and control plants were exposed to high-light (HL) stress (PAR: 1200 mol m–2 s–1) to study whether pre-treatment with UV-B affected the photoprotective mechanisms of the plants against photoinhibition. At regular time intervals leaf discs were taken to perform chlorophyll a fluorescence and oxygen evolution measurements to assess damage to the photosystems. Also, after 1 h of HL treatment the concentration of xanthophyll cycle pigments was determined. A significantly slower decline of maximum quantum efficiency of PSII (F
v/F
m), together with a slower decline of oxygen evolution during HL stress was observed in leaf discs of UV-B treated plants compared to controls in both plant species. This indicated an increased tolerance to HL stress in UV-B treated plants. The total pool of xanthophyll cycle pigments was increased in UV-B treated pea plants compared to controls, but in bean no significant differences were found between treatments. However, in bean plants thiol concentrations were significantly enhanced by UV-B treatment, and UV-absorbing compounds increased in both species, indicating a higher antioxidant capacity. An increased leaf thickness, together with increases in antioxidant capacity could have contributed to the higher protection against photoinhibition in UV-B treated plants. 相似文献
20.
The use of chlorophyll fluorescence as a method for detecting and monitoring plant stress arising from Tetranychus urticae (Koch) feeding injury was investigated. The effect of mite density (1–32 mites per 1.5 cm2 of leaf) and the duration of the feeding period (1–5 days) on the chlorophyll fluorescence parameters of bean (Phaseolus vulgaris) leaves were examined. Changes in chlorophyll fluorescence parameters were dependent both on mite density and duration of feeding. Decreases in F
o, the initial fluorescence and F
m, the maximum fluorescence led to a decrease in the ratio of variable to maximum fluorescence, F
v/F
m. The decrease in F
v/F
m is typical of the response of many plants to a wide range of environmental stresses and indicates a reduced efficiency of photosystem II (PSII) photochemistry. T
1/2, which is proportional to the pool size of electron acceptors on the reducing side of PSII, was also reduced in response to mite-feeding injury. The leaf chlorophyll content decreased with increasing mite density and duration of feeding but did not appear to contribute to the decrease in F
v/F
m. Chlorophyll fluorescence is an effective method for detecting and monitoring stress in T. urticae-injured bean leaves. 相似文献