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1.
Is increased UV-B a threat to crop photosynthesis and productivity? 总被引:17,自引:0,他引:17
It has been suggested that increases in ground-level UV-B, as a result of stratospheric ozone depletion, may have major deleterious effects on crop photosynthesis and productivity. The direct consequences of such effects have been projected by some as a world-wide decrease in crop yields of 20–25%. Further losses, or unrealized gains, have also been suggested as a result of increased UV-B counteracting the beneficial effects of elevated atmospheric CO2. Deleterious UV-B effects may be largely partitioned between damage to the plant genome and damage to the photosynthetic machinery. Direct damage to DNA is a common result of absorption of high energy UV-B photons. However, most plants possess repair mechanisms adequate to deal with the levels of damage expected from projected increases in ground-level UV-B. In addition, most plants have the ability to increase production of UV-absorbing compounds in their leaves as a result of exposure to UV-B, UV-A and visible radiation. These compounds contribute substantially to reducing UV-B damage in situ. It has also been shown that in some plants, under the proper conditions, almost every facet of the photosynthetic machinery can be damaged directly by very high UV-B exposures. However, electron transport, mediated by Photosystem II (PS II) appears to be the most sensitive part of the system. Various laboratories have reported damage to virtually all parts of the PS II complex from the Mn binding site to the plastoquinone acceptor sites on the opposite surface of the thylakoid membrane. However, a critical review of the literature with emphasis on exposure protocols and characterization of the radiation environment, revealed that most growth chamber and greenhouse experiments and very many field experiments have been conducted at unrealistic or indeterminate UV-B exposure levels, especially with regard to the spectral balance of their normal radiation environment. Thus, these experiments have led directly to large overestimates of the potential for damage to crop photosynthesis and yield within the context of 100 year projections for stratospheric ozone depletion. Indeed, given the massive UV-B exposures necessary to produce many of these effects, we suggest it is unlikely that they would occur in a natural setting and urge reconsideration of the purported impacts of projected increases of UV-B on crop productivity.Abbreviations Ci
leaf internal CO2 partial pressure
- CPD
cyclobutane pyrimidine dimer
- CVY
cultivar-year, one crop cultivar grown for one season
- FV/FM
variable chlorophyll fluorescence ratio
- kJ m–2 d–1
daily radiation energy flux
- PAR
photosynthetically active radiation
- PAS300
UV-BBE weighted by the generalized plant action spectrum normalized to 300 nm
- TOMS
total ozone mapping spectrometer instrument mounted aboard the National Aeronautics and Space Administration's Nimbus-7 satellite
- UV-A
ultraviolet-A radiation (400 nm>320 nm)
- UV-B
ultraviolet-B radiation (320 nm280 nm)
- UV-BBE
biologically effective UV-B (in this paper, irradiance weighted by the generalized plant action spectrum)
The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
2.
The effect of UV-B radiation on photosynthesis and respiration of phytoplankton,benthic macroalgae and seagrasses 总被引:5,自引:0,他引:5
Several species of marine benthic algae, four species of phytoplankton and two species of seagrass have been subjected to ultraviolet B irradiation for varying lengths of time and the effects on respiration, photosynthesis and fluorescence rise kinetics studied. No effect on respiration was found. Photosynthesis was inhibited to a variable degree in all groups of plants after irradiation over periods of up to 1 h and variable fluorescence was also inhibited in a similar way. The most sensitive plants were phytoplankton and deep-water benthic algae. Intertidal benthic algae were the least sensitive to UV-B irradiation and this may be related to adaptation, through the accumulation of UV-B screening compounds, to high light/high UV-B levels. Inhibition of variable fluorescence (Fv) of the fluorescence rise curve was a fast and sensitive indicator of UV-B damage. Two plants studied, a brown alga and a seagrass, showed very poor recovery of Fv over a period of 32 h.Abbreviations Fm-
fluorescence yield with reaction centres closed
- Fo-
fluorescence yield with reaction centres open
- Fv-
variable fluorescence
- PAR-
photosynthetically active radiation
- P680-
primary donor of Photosystem II
- O-
primary quencher of Photosystem II
- QA-
primary quinone acceptor of Photosystem II
- UV-B-
ultraviolet B 相似文献
3.
The regulation of Crassulacean acid metabolism (CAM) in the fern Pyrrosia piloselloides (L.) Price was investigated in Singapore on two epiphytic populations acclimated to sun and shade conditions. The shade fronds were less succulent and had a higher chlorophyll content although the chlorophyll a:b ratio was lower and light compensation points and dark-respiration rates were reduced. Dawn-dusk variations in titratable acidity and carbohydrate pools were two to three times greater in fronds acclimated to high photosynthetically active radiation (PAR), although water deficits were also higher than in shade fronds. External and internal CO2 supply to attached fronds of the fern was varied so as to regulate the magnitude of CAM activity. A significant proportion of titratable acidity was derived from the refixation of respiratory CO2 (27% and 35% recycling for sun and shade populations, respectively), as measured directly under CO2-free conditions. Starch was shown to be the storage carbodydrate for CAM in Pyrrosia, with a stoichiometric reduction of C3-skeleton units in proportion to malic-acid accumulation. Measurements of photosynthetic O2 evolution under saturating CO2 were used to compare the light responses of sun and shade fronds for each CO2 supply regime, and also following the imposition of a photoinhibitory PAR treatment (1600 mol·m-2·s-1 for 3 h). Apparent quantum yield declined following the high-PAR treatment for sun- and shade-adapted plants, although for sun fronds CAM activity derived from respiratory CO2 prevented any further reduction in photosynthetic efficiency. Recycling of respiratory CO2 by shade plants could only partly prevent photoinhibitory damage. These observations provide experimental evidence that respiratory CO2 recycling, ubiquitous in CAM plants, may have developed so as to alleviate photoinhibition.Abbreviations and symbols CAM
Crassulacean acid metabolism
- FM
maximal photosystem II fluorescence
- FT
terminal steady-state fluorescence
- PAR
photosynthetically active radiation, 400–700 nm
- H+
(dawn-dusk) variation in titratable acidity 相似文献
4.
The effects of ultraviolet-B (UV-B: 280-320 nm) radiation on the photosynthetic pigments, primary photochemical reactions of thylakoids and the rate of carbon assimilation (Pn) in the cotyledons of clusterbean (Cyamopsis tetragonoloba) seedlings have been examined. The radiation induces an imbalance between the energy absorbed through the photophysical process of photosystem (PS) II and the energy consumed for carbon assimilation. Decline in the primary photochemistry of PS II induced by UV-B in the background of relatively stable Pn, has been implicated in the creation of the energy imbalance. The radiation induced damage of PS II hinders the flow of electron from QA to QB resulting in a loss in the redox homeostasis between the QA to QB leading to an accumulation of QA−. The accumulation of QA− generates an excitation pressure that diminishes the PS II-mediated O2 evolution, maximal photochemical potential (Fv/Fm) and PS II quantum yield (ΦPS II). While UV-B radiation inactivates the carotenoid-mediated protective mechanisms, the accumulation of flavonoids seems to have a small role in protecting the photosynthetic apparatus from UV-B onslaught. The failure of protective mechanisms makes PS II further vulnerable to the radiation and facilitates the accumulation of malondialdehyde (MDA) indicating the involvement of reactive oxygen species (ROS) metabolism in UV-B-induced damage of photosynthetic apparatus of clusterbean cotyledons. 相似文献
5.
Photosystem I-dependent cyclic electron transport is important in controlling Photosystem II activity in leaves under conditions of water stress 总被引:9,自引:0,他引:9
Eva Katona Spidola Neimanis Gerald Schönknecht Ulrich Heber 《Photosynthesis research》1992,34(3):449-464
Leaves of the C3 plant Brassica oleracea were illuminated with red and/or far-red light of different photon flux densities, with or without additional short pulses of high intensity red light, in air or in an atmosphere containing reduced levels of CO2 and/or oxygen. In the absence of CO2, far-red light increased light scattering, an indicator of the transthylakoid proton gradient, more than red light, although the red and far-red beams were balanced so as to excite Photosystem II to a comparable extent. On red background light, far-red supported a transthylakoid electrical field as indicated by the electrochromic P515 signal. Reducing the oxygen content of the gas phase increased far-red induced light scattering and caused a secondary decrease in the small light scattering signal induced by red light. CO2 inhibited the light-induced scattering responses irrespective of the mode of excitation. Short pulses of high intensity red light given to a background to red and/or far-red light induced appreciable additional light scattering after the flashes only, when CO2 levels were decreased to or below the CO2 compensation point, and when far-red background light was present. While pulse-induced light scattering increased, non-photochemical fluorescence quenching increased and F0 fluorescence decreased indicating increased radiationless dissipation of excitation energy even when the quinone acceptor QA in the reaction center of Photosystem II was largely oxidized. The observations indicate that in the presence of proper redox poising of the chloroplast electron transport chain cyclic electron transport supports a transthylakoid proton gradient which is capable of controlling Photosystem II activity. The data are discussed in relation to protection of the photosynthetic apparatus against photoinactivation.Abbreviations F, FM, F'M, F"M, F0, F'0
chlorophyll fluorescence levels
- exc
quantum efficiency of excitation energy capture by open Photosystem II
- PS II
quantum efficiency of electron flow through Photosystem II
- P515
field indicating rapid absorbance change peaking at 522 nm
- P700
primary donor of Photosystem I
- QA
primary quinone acceptor in Photosystem II
- QN
non-photochemical fluorescence quenching
- Qq
photochemical quenching of chlorophyll fluorescence 相似文献
6.
Chlorella was used to study the effects of dehydration on photosynthetic activities. The use of unicellular green algae assured that the extent of dehydration was uniform throughout the whole cell population during the course of desiccation. Changes in the activities of the cells were monitored by measurements of fluorescence induction kinetics. It was found that inhibition of most of the photosynthetic activities started at a similar level of cellular water content. They included CO2 fixation, photochemical activity of Photosystem II and electron transport through Photosystem I. The blockage of electron flow through Photosystem I was complete and the whole transition occurred within a relative short time of dehydration. On the other hand, the suppression of Photosystem II activity was incomplete and the transition took a longer time of dehydration. Upon rehydration, the inhibition of Photosystem II activity was fully reversible when samples were in the middle of the transition, but was not thereafter. The electron transport through Photosystem I was also reversible during the transition, but was only partially afterward.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethyl urea
- Fm
maximum fluorescence yield
- F0
non-variable fluorescence level emitted when all PS II centers are open
- Fv
variable part of fluorescence
- PS
photosystem
- QA
primary quinone acceptor of Photosystem II 相似文献
7.
Low light adapted cultures of the marine diatom Thalassiosira pseudonana (3H) were cultured and incubated for 30 min under different ultraviolet (UV) wavelengths of near monochromatic light with
and without background photosynthetically active radiation (PAR, 380–700 nm). Maximum damage to the quantum yield for stable
charge separations was found in the UVB (280-320 nm) wavelengths without background PAR light while the damage under PAR was
30% less. UV induced damage to carbon fixation in the cells was described by a function similar to non-linear functions of
inhibiting irradiance previously published with the exception that damage was slightly higher in the UVA (320–380). Various
measurements of fluorescent transients were measured and the results indicate localised damage most likely on the acceptor
side of the Photosystem II reaction center. However, dark adapted measurements of fluorescence transients with and without
DCMU do not result in similar functions. This is also true for the relationships between fluorescence transients and carbon
fixation for this species of marine diatom. The correlation between the weightings
H from measurements of carbon fixation and the quantum yield for stable charge separation as calculated from induction curves
with DCMU and without DCMU is R
2 0.44 and R
2 0.78, respectively. The slopes of the two measurements are 3.8 and 1.4, respectively. The strong correlation between the
weightings of the induction curves without DCMU and carbon fixation are due to a loss of electron transport from the reaction
center to plastoquinone. Under these experimental conditions of constant photon flux density (PFD) this is manifested as a
strong linear relationship between the decrease in the operational quantum yield of Photosystem II and carbon fixation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
M. K. Pradhan L. Nayak P. N. Joshi P. K. Mohapatra L. Patro B. Biswal U. C. Biswal 《Photosynthetica》2008,46(3):370-377
Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280–320 nm;
60 μmol m−2 s−1) exposure alone and in combination with photosynthetically active radiation (PAR; 400–800 nm; 200 μmol m−2 s−1) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential
loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O2 evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The
damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of
flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential
changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development
and the ability was modified in UV-B+ PAR exposed samples. 相似文献
9.
Dissipation of absorbed excitation energy as heat, measured by its effect on the quenching of chlorophyll fluorescence, is induced under conditions of excess light in order to protect the photosynthetic apparatus of plants from light-dependent damage. The spectral characteristics of this quenching have been compared to that due to photochemistry in the Photosystem II reaction centre using leaves of Guzmania monostachia. This was achieved by making measurements at 77K when fluorescence emission bands from each type of chlorophyll protein complex can be distinguished. It was demonstrated that photochemistry and non-photochemical dissipation preferentially quench different emission bands and therefore occur by dissimilar mechanisms at separate sites. It was found that photochemistry was associated with a preferential quenching of emission at 688 nm whereas the spectrum for rapidly reversible non-photochemical quenching had maxima at 683 nm and 698 nm, suggesting selective quenching of the bands originating from the light harvesting complexes of Photosystem II. Further evidence that this was occurring in the light harvesting system was obtained from the fluorescence excitation spectra recorded in the quenched and relaxed states.Abbreviations pH
transthylakoid pH gradient
- Fo
minimum level of chlorophyll fluorescence when Photosystem II reaction centres are open
- Fm
maximum level of fluorescence when Photosystem II reaction centres are closed
- Fv
variable fluorescence Fm
minus Fo
- F'o
Fo in any quenched state
- Fm
Fm in any quenched state
- LHCII
light harvesting complexes of Photosystem II
- PSI
Photosystem I
- PS II
Photosystem II
- qN
non-photochemical quenching of chlorophyll fluorescence
- qE
non-photochemical quenching of chlorophyll fluorescence that occurs in the presence of a pH 相似文献
10.
Visser A. J. Tosserams M. Groen M. W. Kalis G. Kwant R. Magendans G. W. H. Rozema J. 《Plant Ecology》1997,128(1-2):209-222
Seedlings of Vicia faba L. (cv. Minica) were grown in a factorial experiment in a greenhouse. The purpose of the study was to determine whether CO2 enrichment and supplemental UV-B radiation affect leaf optical properties and whether the combined effects differ from single factor effects. Seedlings were grown at either 380 mol mol-1 or 750 mol mol-1 CO2 and at four levels of UV-B radiation. After 20 and 40 days of treatment, absorptance, transmittance and reflectance of photosynthetically active radiation (PAR) were measured on the youngest fully developed leaf. On the same leaf, the specific leaf area on a fresh weight basis (SLAfw), chlorophyll content, UV-B absorbance, transmittance of UV light and stomatal index were measured. UV-B radiation significantly increased PAR absorptance and decreased PAR transmittance. The increased PAR absorptance can be explained by an increased chlorophyll content in response to UV-B radiation. Leaf transmittance of UV radiation decreased with increasing UV-B levels mainly caused by increased absorbance of UV absorbing compounds. UV-B radiation decreased both the stomatal density and epidermal cell density of the abaxial leaf surface, leaving the stomatal index unchanged. Effects of CO2 enrichment were less pronounced than those of UV-B radiation. The most important CO2 effect was an increase in stomatal density and epidermal cell density of the adaxial leaf surface. The stomatal index was not affected. No interaction between CO2 and UV-B radiation was found. The results are discussed in relation to the internal light environment of the leaf. 相似文献