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1.
The role of photorespiration during drought stress: an analysis utilizing barley mutants with reduced activities of photorespiratory enzymes 总被引:19,自引:2,他引:19
A. WINGLER W. P. QUICK R. A. BUNGARD K. J. BAILEY P. J. LEA & R. C. LEEGOOD 《Plant, cell & environment》1999,22(4):361-373
C i, intercellular CO2 concentrationFv/Fm, quantum efficiency of excitation capture by open photosystem II centresFBPase, fructose-1,6-bisphosphataseGAPDH, glyceraldehyde-3-phosphate dehydrogenaseGDC, glycine decarboxylaseGS-2, chloroplastic glutamine synthetaseHPR, hydroxypyruvate reductasePFD, photon flux densityΦCO2, quantum efficiency of CO2 assimilationΦPSII, quantum efficiency of photosystem II electron transportψ, water potentialqN, non-photochemical chlorophyll a fluorescence quenchingqP, photochemical chlorophyll a fluorescence quenchingRuBP, ribulose-1,5-bisphosphateRubisco, ribulose-1,5-bisphosphate carboxylase-oxygenaseSBPase, sedoheptulose-1,7-bisphosphataseSGAT, serine : glyoxylate aminotransferaseThe significance of photorespiration in drought-stressed plants was studied by withholding water from wild-type barley (Hordeum vulgare L.) and from heterozygous mutants with reduced activities of chloroplastic glutamine synthetase (GS-2), glycine decarboxylase (GDC) or serine : glyoxylate aminotransferase (SGAT). Well-watered plants of all four genotypes had identical rates of photosynthesis. Under moderate drought stress (leaf water potentials between –1 and –2 MPa), photosynthesis was lower in the mutants than in the wild type, indicating that photorespiration was increased under these conditions. Analysis of chlorophyll a fluorescence revealed that, in the GDC and SGAT mutants, the lower rates of photosynthesis coincided with a decreased quantum efficiency of photosystem II and increased non-photochemical dissipation of excitation energy. Correspondingly, the de-epoxidation state of xanthophyll-cycle carotenoids was increased several-fold in the drought-stressed GDC and SGAT mutants compared with the wild type. Accumulation of glycine in the GDC mutant was further evidence for increased photorespiration in drought-stressed barley. The effect of drought on the photorespiratory enzymes was determined by immunological detection of protein abundance. While the contents of GS-2 and P- and H-protein of the GDC complex remained unchanged as drought stress developed, the content of NADH-dependent hydroxypyruvate reductase increased. Enzymes of the Benson–Calvin cycle, on the other hand, were either not affected (ribulose-1,5-bisphosphate carboxylase-oxygenase and plastidic fructose-1,6-bisphosphatase) or declined (sedoheptulose- 1,7-bisphosphatase and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase). These data demonstrate that photorespiration was enhanced during drought stress in barley and that the control exerted by photorespiratory enzymes on the rate of photosynthetic electron transport and CO2 fixation was increased. 相似文献
2.
The regulation of photosystem II (PSII) by light-, CO2-, and O2-dependent changes in the capacity for carbon metabolism was studied. Estimates of the rate of electron transport through PSII were made from gas-exchange data and from measurements of chlorophyll fluorescence. At subsaturating photon-flux density (PFD), the rate of electron transport was independent of O2 and CO2. Feedback on electron transport was observed under two conditions. At saturating PFD and low partial pressure of CO2, p(CO2), the rate of electron transport increased with p(CO2). However, at high p(CO2), switching from normal to low p(O2) did not affect the net rate of photosynthetic CO2 assimilation but the rate of electron-transport decreased by an amount related to the change in the rate of photorespiration. We interpret these effects as 1) regulation of ribulose-1,5-bisphosphatecarboxylase (RuBPCase, EC 4.1.1.39) activity to match the rate of electron transport at limiting PFD, 2) regulation of electron-transport rate to match the rate of RuBPCase at low p(CO2), and 3) regulation of the electron-transport rate to match the capacity for starch and sucrose synthesis at high p(CO2) and PFD. These studies provide evidence that PSII is regulated so that the capacity for electron transport is matched to the capacity for other processes required by photosynthesis, such as ribulose-bisphosphate carboxylation and starch and sucrose synthesis. We show that at least two mechanisms contribute to the regulation of PSII activity and that the relative engagement of these mechanisms varies with time following a step change in the capacity for ribulose-bisphosphate carboxylation and starch and sucrose synthesis. Finally, we take advantage of the relatively slow activation of deactivated RuBPCase in vivo to show that the activation level of this enzyme can limit the rate of electron transport as evidenced by increased feedback on PSII following a step change in p(CO2). As RuBPCase as activated, the feedback on PSII declined.Abbreviations and symbols JC
electron-transport rate calculated from CO2-assimilation measurements
- JF
electron-transport rate calculated from fluorescence parameters
- PFD
photon-flux density
- qE
energy-dependent quenching
- PSII
photosystem II
- qQ
Q-dependent quenching
- QY
quantum yield
- RuBPCase
ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)
C.I.W. publication No. 1015 相似文献
3.
Analysis of limitations to CO2 assimilation on exposure of leaves of two Brassica napus cultivars to UV-B 总被引:1,自引:1,他引:0
Apex and Bristol cultivars of oilseed rape (Brassica napus) were irradiated with 0.63 W m?2 of UV-B over 5 d. Analyses of the response of net leaf carbon assimilation to intercellular CO2 concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bis-phosphate on leaf photosynthesis. Simultaneous measurements of chlorophyll fluorescence were used to estimate the maximum quantum efficiency of photosystem II (PSII) photochemistry, the quantum efficiency of linear electron transport at steady-state photosynthesis, and the light and CO2-saturated rate of linear electron transport. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) content and activities were assayed in vitro. In both cultivars the UV-B treatment resulted in decreases in the light-saturated rate of CO2 assimilation, which were accompanied by decreases in carboxylation velocity and Rubisco content and activity. No major effects of UV-B were observed on end-product inhibition and stomatal limitation of photosynthesis or the rate of photorespiration relative to CO2 assimilation. In the Bristol cultivar, photoinhibition of PSII and loss of linear electron transport activity were observed when CO2 assimilation was severely inhibited. However, the Apex cultivar exhibited no major inhibition of PSII photochemistry or linear electron transport as the rate of CO2 assimilation decreased. It is concluded that loss of Rubisco is a primary factor in UV-B inhibition of CO2 assimilation. 相似文献
4.
《Environmental and Experimental Botany》2007,59(1-3):261-268
Experiments were conducted to investigate the photosynthetic activity and thermostability of photosystem II (PSII) in elm seedling (Ulmus pumila) leaves from initiation to full expansion. During leaf development, photosynthesis, measured as CO2 fixation, increased gradually and reached a maximum value when leaves were fully developed. In parallel with the increase of carbon assimilation, chlorophyll content increased. The chlorophyll a fluorescence measurements showed that the maximum quantum yield of PSII primary photochemistry (φpo), the efficiency with which the energy of trapped excitons is converted into the electron transport beyond QA (Ψo) and the quantum yield of electron transport beyond QA (φEo) increased gradually. The low light experiments confirmed these results independently. When subjected to heat stress, young leaves exhibited progressively lower φpo and maximal fluorescence (Fm) values with considerably higher minimal fluorescence (Fo) than mature leaves, demonstrating that PSII in newly initiating leaves is more sensitive to heat stress. Further analysis revealed that PSII structure in newly initiating leaves showed a robust alteration under heat stress, which was reflected by the clear K phase in the OJIP curves. Therefore, we suggest that the enhanced thermostability of PSII in the case of leaf growth might be associated with an improvement of the stability of the oxygen-evolving complex (OEC) to heat stress during leaf development. 相似文献
5.
Huan-Xin Jiang Ning Tang Jin-Gui Zheng Yan Li Li-Song Chen 《Physiologia plantarum》2009,137(3):298-311
Limited data are available on the effects of phosphorus (P) and aluminum (Al) interactions on Citrus spp. growth and photosynthesis. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 50, 100, 250 and 500 μM KH2PO4× 0 and 1.2 mM AlCl3· 6H2O. Thereafter, P and Al in roots, stems and leaves, and leaf chlorophyll (Chl), CO2 assimilation, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and Chl a fluorescence (OJIP) transients were measured. Under Al stress, P increased root Al, but decreased stem and leaf Al. Shoot growth is more sensitive to Al than root growth, CO2 assimilation and OJIP transients. Al decreased CO2 assimilation, Rubisco activity and Chl content, whereas it increased or did not affect intercellular CO2 concentration. Al affected CO2 assimilation more than Rubisco and Chl under 250 and 500 μM P. Al decreased root, stem and leaf P, leaf maximum quantum yield of primary photochemistry (Fv/Fm) and total performance index (PItot,abs), but increased leaf minimum fluorescence (Fo), relative variable fluorescence at K‐ and I‐steps. P could alleviate Al‐induced increase or decrease for all these parameters. We conclude that P alleviated Al‐induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from photosystem II (PSII) donor side up to the reduction of end acceptors of photosystem I (PSI), thus preventing photosynthesis inhibition through increasing Al immobilization in roots and P level in roots and shoots. Al‐induced impairment of the whole photosynthetic electron transport chain may be associated with growth inhibition. 相似文献
6.
Georgieva K Szigeti Z Sarvari E Gaspar L Maslenkova L Peeva V Peli E Tuba Z 《Planta》2007,225(4):955-964
The functional state of the photosynthetic apparatus of flowering homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and subsequent rehydration was investigated in order to characterize some of the mechanisms by which resurrection
plants survive drought stress. The changes in the CO2 assimilation rate, chlorophyll fluorescence parameters, thermoluminescence, fluorescence imaging and electrophoretic characteristics
of the chloroplast proteins were measured in control, moderately dehydrated (50% water content), desiccated (5% water content)
and rehydrated plants. During the first phase of desiccation the net CO2 assimilation decline was influenced by stomatal closure. Further lowering of net CO2 assimilation was caused by both the decrease in stomatal conductance and in the photochemical activity of photosystem II.
Severe dehydration caused inhibition of quantum yield of PSII electron transport, disappearance of thermoluminescence B band
and mainly charge recombination related to S2QA− takes place. The blue and green fluorescence emission in desiccated leaves strongly increased. It could be suggested that
unchanged chlorophyll content and amounts of chlorophyll–proteins, reversible modifications in PSII electron transport and
enhanced probability for non-radiative energy dissipation as well as increased polyphenolic synthesis during desiccation of
Haberlea contribute to drought resistance and fast recovery after rehydration. 相似文献
7.
Chl, chlorophyllChl a/b, ratio of chlorophyll a to chlorophyll bCyt f, cytochrome fFR, far-red lightLFR, low irradiance, far-red enriched growth lightLHCII, light harvesting complex associated with PSIILW, low irradiance, white growth lightMW, moderate irradiance, white growth lightPAR, photosynthetically active radiationPmax, light and CO2 saturated photosynthetic ratePSI, photosystem IPSII, photosystem IIFour plant species (Chamerion angustifolium, Digitalis purpurea, Brachypodium sylvaticum and Plantago lanceolata) which have previously been shown to demonstrate contrasting photosynthetic acclimatory responses to the light environment ( 33 , Plant, Cell and Environment 20, pp. 438–448) were analysed at a biochemical level. Plants were grown under low irradiance with a shade-type spectrum (LFR: 50μmol quanta m–2 s–1), moderately high white light (MW: 300μmol quanta m–2 s–1) and low irradiance white light (LW: 50μmol quanta m–2 s–1). The effects of light quality upon chlorophyll content and photosynthetic capacity were found to be species-dependent. A far-red dependent reduction in chlorophyll was found in three species, and an irradiance-dependent reduction was found in B. sylvaticum, which showed the greatest alteration in the xanthophyll cycle pool size of all species tested under these conditions. Chlorophyll a/b ratios were sensitive to both light quality and quantity in C. angustifolium and D. purpurea, being highest in MW, lowest in LFR, and intermediate in LW, whilst the other species showed no response. Ratios of photosystem II to photosystem I (PSII and PSI) demonstrated a strong irradiance-associated increase in all species except B. sylvaticum, whereas an increase in PSII/PSI in LFR compared to LW conditions was present in all species. A change in chlorophyll a/b was not always associated with a change in PSII/PSI, suggesting that the level of LHCII associated with each PSII varied in some species. Cytochrome f content showed an irradiance-dependent effect only, indicating a relationship with the capacity of electron transport. It is concluded that differing strategies of acclimation to the light environment demonstrated by these species results from differing strengths of expression of a series of independently regulated changes in the levels of photosynthetic components. 相似文献
8.
C. D. Stylinski W. C. Oechel J. A. Gamon D. T. Tissue F. Miglietta A. Raschi 《Plant, cell & environment》2000,23(12):1353-1362
Lifelong exposure to elevated concentrations of atmospheric CO2 may enhance carbon assimilation of trees with unlimited rooting volume and consequently may reduce requirements for photoprotective pigments. In early summer the effects of elevated [CO2] on carboxylation and light utilization of mature Quercus pubescens trees growing under chronic [CO2] enrichment at two CO2 springs and control sites in Italy were examined. Net photosynthesis was enhanced by 36 to 77%. There was no evidence of photosynthetic downregulation early in the growing season when sink demand presumably was greatest. Specifically, maximum assimilation at saturating [CO2], electron transport capacity, and Rubisco content, activity and carboxylation capacity were not significantly different in trees growing at the CO2 springs and their respective control sites. Foliar biochemical content, leaf reflectance index of chlorophyll pigments (NDVI), and photochemical efficiency of PSII (ΔF/Fm′) also were not significantly affected by [CO2] enrichment except that starch content and ΔF/Fm′ tended to be higher at one spring (42 and 15%, respectively). Contrary to expectation, prolonged elevation of [CO2] did not reduce xanthophyll cycle pigment pools or alter mid‐day values of leaf reflectance index of xanthophyll cycle pigments (PRI), despite the enhancement of carbon assimilation. However, both these pigments and PRI were well correlated with electron transport capacity. 相似文献
9.
Photosynthetic Potential and its Association with Lipid Peroxidation in Response to High Temperature at Different Leaf Ages in Maize 总被引:2,自引:0,他引:2
Zhenzhu Xu Guangsheng Zhou Guangxuan Han Yijun Li 《Journal of Plant Growth Regulation》2011,30(1):41-50
High temperature generally constrains plant growth and photosynthesis in many regions of the world; however, little is known
about how photosynthesis responds to high temperature with regard to different leaf ages. The synchronous changes in gas exchange
and chlorophyll fluorescence at three leaf age levels (just fully expanded, mature, and older leaves) of maize (Zea mays L.) were determined at three temperatures (30°C as a control and 36 and 42°C as the higher temperatures). High temperature
significantly decreased the net CO2 assimilation rate (A), stomatal conductance (g
s), maximal efficiency of photosystem II (PSII) photochemistry (F
v/F
m), efficiency of excitation energy capture by open PSII reaction centers (
F¢\textv /F¢\textm F^{\prime}_{\text{v}} /F^{\prime}_{\text{m}} ), photochemical quenching of variable chlorophyll fluorescence (q
P), and the electron transport rate (ETR), whereas minimal fluorescence yield (F
0) and nonphotochemical quenching of variable chlorophyll fluorescence (q
N) were increased. The youngest fully expanded leaves had higher A, ETR, and q
P compared with older leaves. Higher temperature with old leaves led to significant malondialdehyde (MDA) accumulation, a proxy
for lipid peroxidation damage from active oxygen species (AOS). MDA content was significantly negatively correlated with A, F
v/F
m,
F¢\textv /F¢\textm F^{\prime}_{\text{v}} /F^{\prime}_{\text{m}} , and q
P. Thus, the results suggest that photosynthetic potentials, including stomatal regulation and PSII activity, may be restricted
at high temperature, together with increasing cell peroxidation, which may be closely associated with leaf age. 相似文献
10.
The influence of chronic exposure to UV-B and UV-A radiation on growth and photosynthesis of two polar marine diatoms (Pseudonitzschia seriata and Nitzschia sp.) was investigated in cultures exposed to moderate photon fluences for 3–7 days. Population growth rates were diminished 50% by UV-B. Fluorescence induction kinetics of photo-system II (PSII) revealed that UV-B caused lower Fv/Fm ratios and half-rise times, indicating damage to the reaction center of PSII and to related elements of the photosynthetic electron transport chain. Carbon assimilation rates per cell and per chlorophyll a were nonetheless highest for UV-B—exposed populations, which also had the highest chlorophyll a content per cell. The UV-B—exposed cells were, however, more vulnerable to visible light-induced photoinhibition. Exposure to UV-A in the absence of UV-B had little effect on growth, fluorescence induction of PSII, or chlorophyll a contents but did have some inhibitory effects on carbon assimilation per chlorophyll a and per cell. The increased photosynthetic capacity of UV-B-exposed cells suggested some ability to compensate for damage to the photosynthetic apparatus. 相似文献
11.
To investigate the photoinhibition of photosynthesis in ‘Honeycrisp’ apple (Malus domestica Borkh. cv. Gala) leaves with zonal chlorosis, we compared pigments, CO2 assimilation and chlorophyll (Chl) a fluorescence (OJIP) transient between chlorotic leaves and normal ones. Chl and carotenoids (Car) contents, Chl a/b ratio, and absorptance were lower in chlorotic leaves than in normal ones, whereas Car/Chl ratio was higher in the former.
Although CO2 assimilation and stomatal conductance were lower in chlorotic leaves, intercellular CO2 concentration did not differ significantly between the two leaf types. Compared with normal leaves, chlorotic ones had increased
deactivation of oxygen-evolving complexes (OEC), minimum fluorescence (F
o), dissipated energy, relative variable fluorescence at L-, W-, J- and I-steps, and decreased maximum fluorescence (F
m), maximum quantum yield for primary photochemistry (F
v
/F
m or TRo/ABS), quantum yield for electron transport (ETo/ABS), quantum yield for the reduction of end acceptors of photosystem I (PSI) (φRo and REo/ABS), maximum amplitude of IP phase, amount of active photosystem II (PSII) reaction centers (RCs) per cross section (CS)
and total performance index (PItot,abs). In conclusion, photoinhibition occurs at both the donor (i.e., the OEC) and the acceptor sides of PSII in chlorotic leaves.
The acceptor side is damaged more severely than the donor side, which possibly is the consequence of over-reduction of PSII
due to the slowdown of Calvin cycle. In addition to decreasing light absorptance by lowering Chl level, energy dissipation
is enhanced to protect chlorotic leaves from photo-oxidative damage. 相似文献
12.
Ernesto Olvera-González Daniel Alaniz-Lumbreras Rumen Ivanov-Tsonchev Jesús Villa-Hernández Ismael de la Rosa-Vargas Irineo López-Cruz Héctor Silos-Espino Alfredo Lara-Herrera 《Plant Growth Regulation》2013,69(2):117-123
The effects of pulsed light based-LEDs at eleven frequencies (0.1, 1, 10, 50, 100, 500 Hz, 1, 5, 10, 50 and 100 kHz) programmed at 50 % duty cycle were analyzed, obtaining important parameters of the fluorescence emission of chlorophyll such as: maximum fluorescence (Fm′), minimum fluorescence, the fluorescence emission in steady state, maximum efficiency of PSII (Fv′/Fm′), the fraction of PSII centers that are open, photochemical quenching, nonphotochemical quenching (NPQ), quantum efficiency of photosystem II (ΦPSII), electron transport rate (ETR) and quantum yield of CO2 assimilation (?CO2). For the study and validation of the results obtained in the experiments, the analysis of variance (ANOVA) was applied 0for each parameter with confidence intervals of 95 %. The results show that the frequencies of pulsed light had positive and negative effects on the fluorescence parameters with respect to the control treatment (continuous light). The frequencies that generated the best performance of Fv′/Fm′, NPQ, ΦPSII, ETR, ?CO2 in tomato plants were 0.1, 1, 100 Hz, and 1 kHz. The increase obtained in these parameters can represent an optimal growth and productivity conditions for optimal energy consumption. 相似文献
13.
R. VALENTINI D. EPRON P. DE ANGELIS G. MATTEUCCI E. DREYER 《Plant, cell & environment》1995,18(6):631-640
Diurnal time courses of net CO2 assimilation rates, stomatal conductance and light-driven electron fluxes were measured in situ on attached leaves of 30-year-old Turkey oak trees (Quercus cerris L.) under natural summer conditions in central Italy. Combined measurements of gas exchange and chlorophyll a fluorescence under low O2 concentrations allowed the demonstration of a linear relationship between the photochemical efficiency of PSII (fluorescence measurements) and the apparent quantum yield of gross photosynthesis (gas exchange). This relationship was used under normal O2 to compute total light-driven electron fluxes, and to partition them into fractions used for RuBP carboxylation or RuBP oxygenation. This procedure also yielded an indirect estimate of the rate of photorespiration in vivo. The time courses of light-driven electron flow, net CO2 assimilation and photorespiration paralleled that of photosynthetic photon flux density, with important afternoon deviations as soon as a severe drought stress occurred, whereas photochemical efficiency and maximal fluorescence underwent large but reversible diurnal decreases. The latter observation indicated the occurrence of a large non-photochemical energy dissipation at PSII. We estimated that less than 60% of the total photosynthetic electron flow was used for carbon assimilation at midday, while about 40% was devoted to photorespiration. The rate of carbon loss by photorespiration (R1) reached mean levels of 56% of net assimilation rates. The potential application of this technique to analysis of the relative contributions of thermal de-excitation at PSII and photorespiratory carbon recycling in the protection of photosynthesis against stress effects is discussed. 相似文献
14.
采用盆栽试验方法,以NaCl为盐分模拟不同盐度环境,研究了施氮(N)对盐环境下生长的甜菜(Beta vulgaris)功能叶光系统Ⅱ (PSⅡ)荧光特性的影响及光合色素含量的变化.结果表明:在轻度、中度及重度盐环境下,施N均能增大PSⅡ最大光化学效率(Fv/Fm)、PSⅡ潜在活性(Fv/Fo)、PSⅡ实际光量子产量(Y(Ⅱ))、非调节性能量耗散的量子产量(Y(NO))、相对电子传递速率(ETR)及光化学猝灭系数(qp),且在适宜的施N范围内(0-1.2 g·kg-1)上述参数随施N量的增加而增大.各叶绿素荧光参数光响应的结果表明,随着光强的增加,各处理下调节性能量耗散的量子产量(KNPQ))、ETR及非光化学猝灭系数(NPQ)旱上升趋势,相反,Y(Ⅱ)、Y(NO)及qp则呈下降趋势,在有效的光强范围内(0-1 000 μmol·m-2·s-1)施N提高了甜菜功能叶PSⅡ反应中心的开放程度,并且在高光强下调节PSⅡ耗散掉过剩的光能以避免对其反应中心造成伤害.各盐度环境下施N也显著增加了甜菜功能叶叶绿素与类胡萝卜素含量,增大了叶绿素a/叶绿素b值,且叶绿素与类胡萝卜素含量随施N水平的增加而增加.说明盐环境下施N能够增强甜菜功能叶PSⅡ的活性,提高PSⅡ光能利用率,从而增强其对盐渍环境的适应性. 相似文献
15.
Simultaneous measurements of chlorophyll (Chl) fluorescence and CO2 assimilation (A) in Vicia faba leaves were taken during the first weeks of growth to evaluate the protective effect of 24-epibrassinolide (EBR) against
damage caused by the application of the herbicide terbutryn (Terb) at pre-emergence. V. faba seeds were incubated for 24 h in EBR solutions (2 × 10−6 or 2 × 10−5 mM) and immediately sown. Terb was applied at recommended doses (1.47 or 1.96 kg ha−1) at pre-emergence. The highest dose of Terb strongly decreased CO2 assimilation, the maximum quantum yield of PSII photochemistry in the dark-adapted state (F
V/F
M), the nonphotochemical quenching (NPQ), and the effective quantum yield (ΔF/F′M) during the first 3–4 weeks after plant emergence. Moreover, Terb increased the basal quantum yield of nonphotochemical processes
(F
0/F
M), the degree of reaction center closure (1 − q
p), and the fraction of light absorbed in PSII antennae that was dissipated via thermal energy dissipation in the antennae
(1 − F′V/F′M). The herbicide also significantly reduced plant growth at the end of the experiment as well as plant length, dry weight,
and number of leaves. The application of EBR to V. faba seeds before sowing strongly diminished the effect of Terb on fluorescence parameters and CO2 assimilation, which recovered 13 days after plant emergence and showed values similar to those of control plants. The protective
effect of EBR on CO2 assimilation was detected at a photosynthetic photon flux density (PFD) of 650 μmol m−2 s−1 and the effect on ΔF/F′M and photosynthetic electron transport (J) was detected under actinic lightings up to 1750 μmol m−2 s−1. The highest dose of EBR also counteracted the decrease in plant growth caused by Terb, and plants registered the same growth
values as controls. 相似文献
16.
In the present study, photosynthetic parameters including gas exchanges, pigment contents, and chlorophyll fluorescence, were compared in two contrasting local Medicago truncatula lines TN6.18 and TN8.20, in response to salt added to the nutrient solution. Plants were cultivated under symbiotic nitrogen fixation (SNF) after inoculation with a reference strain Sinorhizobium meliloti 2011, a very tolerant strain to salinity (700 mM NaCl), and grown in a controlled glasshouse. On one month old plants (with active SNF), salt treatment (75 mM NaCl) was gradually applied. Photosynthesis, assimilating pigments and chlorophyll fluorescence were monitored throughout the experiment during both short and long terms, compared to control (non-saline) conditions. A genotypic variation in salt tolerance was found; TN6.18 was the more sensitive to salinity. The relative tolerance of TN8.20 was concomitant with the highest photochemical quenching coefficient (qP) affecting the maximum quantum yield of PSII (Y); the real quantum yield (?exc) was the most affected in the sensitive line. Moreover, stomatal and PSII reaction centers activities differed clearly between the studied lines. We found that the effect of salinity on photosynthesis of M. truncatula was related to PSII activity reduction rather than to stomatal conductance limitation. Photosynthesis was reduced by the inhibition of CO2 assimilation caused by PSII damage. This was clearly estimated by the Y, ?exc and especially by the quantum yield of electron transport of PSII (ΦPSII). Thus, on the basis of our results on the two local M. truncatula lines, we recommend the use of chlorophyll fluorescence as non-destructive screening method to discriminate susceptible and resistant legumes to salt stress. 相似文献
17.
Geum montanum L. is an alpine plant usually found at altitudes between 1700 and 2600 m. Its wintergreen leaves can be subjected to very
low temperatures and at the same time receive high photon flux densities at the beginning of the growth season when the snow
melts. We report results of a study, performed with classical methods of biophysics, showing that leaves of G. montanum were remarkably tolerant to sunlight even at low temperatures. This tolerance results from the interplay of photorespiration
and CO2 photosassimilation. When temperatures approach 0°C, responses include stomatal opening and CO2 uptake even under desiccation stress. This permits linear electron transport that is sufficient to avoid the excessive reduction
of the electron transport chain which is known to lead to photodamage. In addition, excitation energy was shifted from photosystem
(PS)II to PSI which is a very efficient energy quencher. Sensitivity of P700 in PSI to oxidation by far-red light was decreased
and rates of dark reduction of photooxidized P700 were increased by actinic illumination, suggesting activation of cyclic
electron transport. Consistent with this, far-red light was able to decrease the quantum yield of PSII (measured by the F
v/F
m ratio of chlorophyll fluorescence). We suggest that cyclic electron transport decreases the lumenal pH under strong light.
In the presence of zeaxanthin, this increases energy dissipation at the PSII level. At low temperatures, P700 remained strongly
oxidized under high irradiation while the primary electron acceptor of PSII, QA, was largely reduced. This shows efficient control of electron transport presumably at the level of the cytochrome b/f complex
and suggests formation of a protective transthylakoid proton gradient even when linear electron transport is much reduced
in the cold. Thus, several mechanisms cooperate to effectively protect the photosynthetic apparatus of G. montanum from photodamage. We see no indication of destructive “photostress” in this species during the growth season under alpine
low-temperature and drought conditions.
Received: 2 March 1998 / Accepted: 7 January 1999 相似文献
18.
In vivo photosynthetic electron transport does not limit photosynthetic capacity in phosphate-deficient sunflower and maize leaves 总被引:8,自引:0,他引:8
The effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and the in vivo photochemical activity of photosystem II (PSII) were determined in leaves of Helianthus annuus and Zea mays grown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi-deficient leaves. Analysis of chlorophyll a fluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φe), the in vivo quantum yield of PSII photochemistry (φPSII) and the photochemical quenching co-efficient (qP), and increased the non-photochemical quenching co-efficient (qN) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi-deficient sunflower leaves reversed the long-term effects of Pi-deficiency on PSII photochemistry. Feeding Pi-sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long-term Pi-deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long-and short-term responses of photosynthetic machinery to Pi deficiency. The relationship between φPSII and the apparent quantum yield of CO2 assimilation determined at varying light intensity and 21 kPa O2 and 35 Pa CO2 partial pressures in the ambient air was linear in Pi-sufficient and Pi-deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO2 assimilated by the Pi-deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO2 reduction. Therefore, we conclude that in vivo photosynthetic electron transport through PSII did not limit photosynthesis in Pi-deficient leaves of sunflower and maize and that the decreased CO2 assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1-5, bisphosphate, the acceptor for CO2. 相似文献
19.
Because photosynthetic rates in C4 plants are the same at normal levels of O2 (c, 20 kPa) and at c, 2 kPa O2 (a conventional test for evaluating photorespiration in C3 plants) it has been thought that C4 photosynthesis is O2 insensitive. However, we have found a dual effect of O2 on the net rate of CO2 assimilation among species representing all three C4 subtypes from both monocots and dicots. The optimum O2 partial pressure for C4 photosynthesis at 30 °C, atmospheric CO2 level, and half full sunlight (1000 μmol quanta m?2 s?1) was about 5–10 kPa. Photosynthesis was inhibited by O2 below or above the optimum partial pressure. Decreasing CO2 levels from ambient levels (32.6 Pa) to 9.3 Pa caused a substantial increase in the degree of inhibition of photosynthesis by supra-optimum levels of O2 and a large decrease in the ratio of quantum yield of CO2 fixation/quantum yield of photosystem II (PSII) measured by chlorophyll a fluorescence. Photosystem II activity, measured from chlorophyll a fluorescence analysis, was not inhibited at levels of O2 that were above the optimum for CO2 assimilation, which is consistent with a compensating, alternative electron How as net CO2 assimilation is inhibited. At suboptimum levels of O2, however, the inhibition of photosynthesis was paralleled by an inhibition of PSII quantum yield, increased state of reduction of quinone A, and decreased efficiency of open PSII centres. These results with different C4 types suggest that inhibition of net CO2 assimilation with increasing O2 partial pressure above the optimum is associated with photorespiration, and that inhibition below the optimum O2 may be caused by a reduced supply of ATP to the C4 cycle as a result of inhibition of its production photochemically. 相似文献
20.
In leaves of an atrazine-resistant mutant ofSenecio vulgaris the quantum efficiency of CO2 assimilation was reduced by 21% compared to the atrazine-susceptible wild type, and at a light level twice that required to saturate photosynthesis in the wild type the CO2 fixation rate in the mutant was decreased by 15%. In leaves at steady-state photosynthesis there was a measurable increase in the reduction state of the photosystem II (PSII) primary quinone acceptor,Q
A. Although this would lead to a decreased rate of PSII electron transport and may thus explain the decrease in quantum efficiency, this cannot account for the fall in the maximum rate of CO2 fixation. The atrazine-resistant mutant showed an appreciably longer photosynthetic induction time which indicates an effect on carbon metabolism; however, the response of CO2-fixation rate to intercellular CO2 concentration revealed no differences in carboxylation efficiency. There were also no differences in the ability to perform a State 1–State 2 transition between the atrazine-resistant and susceptible biotypes and no difference in the profiles of phosphorylated thylakoid polypeptides. It is concluded that the alteration of the redox equilibrium between PSII quinone electron acceptors in the atrazine-resistant biotype limits appreciably the photosynthetic efficiency in non-saturating light. Additionally, there is a further, as yet unidentified, limitation which decreases photosynthesis in the resistant mutant under light-saturating conditions.Abbreviations and symbols DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
-
F
max
maximum fluorescence emission
-
F
o2
minimal fluorescence emission upon exposure to saturating light flash
-
F
v
variable fluorescence emission
-
F
v2
variable fluorescence emission upon exposure to saturating light flash
- kDa
kilodalton
- PSI, II
photosystems I, II
-
Q
A
primary quinone acceptor of PSH
-
Q
B
secondary quinone acceptor of PSII
- RuBP
ribulose-1,5-bisphosphate 相似文献