Employing the non-invasive techniques of infra-red gas analysis and pulse amplitude modulated chlorophyll fluorometry, we determined the partitioning of photosynthetic electrons between photosynthetic carbon reduction and other reductive processes resulting in the formation of active oxygen species (AOS) in intact green leaves. This we studied in plant species that are adapted to two different agro-climatic conditions, namely the warm plains (76°36'E, 9°32'N) and the cool mountains (1 600 m a.s.l.) in the south Indian state of Kerala. Ground frost and low temperature were more harmful to those species adapted to the warm plains than the ones adapted to the cool mountains. Exposure to low temperature decreased leaf photosynthetic carbon assimilation rates and quantum yield of photochemical activity in species naturally adapted to the warm plains. High irradiances further aggravated the harmful effects of low temperature stress possibly by overproducing AOS. This resulted in severe peroxidative damage as inferred by the accumulation of malondialdehyde (MDA) in the leaves. and B. Alam, J. Jacob.
In sunflower (Helianthus annuus L.) grown under controlled conditions and subjected to drought by withholding watering, net photosynthetic rate (PN) and stomatal conductance (gs) of attached leaves decreased as leaf water potential (Ψw) declined from -0.3 to -2.9 MPa. Although gs decreased over the whole range of Ψw, nearly constant values in the intercellular CO2 concentrations (Ci) were observed as Ψw decreased to -1.8 MPa, but Ci increased as Ψw decreased further. Relative quantum yield, photochemical quenching, and the apparent quantum yield of photosynthesis decreased with water deficit, whereas non-photochemical quenching (qNP) increased progressively. A highly significant negative relationship between qNP and ATP content was observed. Water deficit did not alter the pyridine nucleotide concentration but decreased ATP content suggesting metabolic impairment. At a photon flux density of 550 µmol m-2 s-1, the allocation of electrons from photosystem (PS) 2 to O2 reduction was increased by 51 %, while the allocation to CO2 assimilation was diminished by 32 %, as Ψw declined from -0.3 to -2.9 MPa. A significant linear relationship between mean PN and the rate of total linear electron transport was observed in well watered plants, the correlation becoming curvilinear when water deficit increased. The maximum quantum yield of PS2 was not affected by water deficit, whereas qP declined only at very severe stress and the excess photon energy was dissipated by increasing qNP indicating that a greater proportion of the energy was thermally dissipated. This accounted for the apparent down-regulation of PS2 and supported the protective role of qNP against photoinhibition in sunflower. and W. Tezara, S. Driscoll, D. W. Lawlor.
The effect of high irradiance (HI, photosynthetically active photon flux density of 1 300 µmol m-2 s-1) on net photosynthetic rate (PN), chlorophyll fluorescence parameters, and xanthophyll cycle components were studied in fruit tree bayberry leaves. HI induced the photoinhibition and inactivation of photosystem 2 (PS2) reaction centres (RCs), which was characterized by decreased PN, maximum yield of fluorescence after dark adaptation (Fm), photochemical efficiency of PS2 (Fv/Fm) and quantum yield of PS2 (ΦPS2), and increased reduction state of QA (1-qP) and non-photochemical quenching (NPQ). Initial fluorescence (F0) showed a decrease after the first 2 h, and subsequently increased from the third hour exposure to HI. Furthermore, a greater increase in the ratio (Fi-F0)/(Fp-F0) which is an expression of the proportion of the QB non-reducing PS2 centres, whereas a remarked decrease in the slope of Fi to Fp which represents the rate of QA reduction was observed in leaves after HI exposure. Additionally, HI caused an increase in the pool size of the xanthophyll cycle pigments and sustained elevated contents of zeaxanthin (Z), antheraxanthin (A), and de-epoxidation state (DES) at the end of the irradiation period. During HI, decreased Fm, Fv/Fm, ΦPS2, NPQ, slope of Fi to Fp, V+A+Z, and DES, and increased F0, 1-qP, ratio (Fi-F0)/(Fp-F0), and V were observed in dithiothreitol (DTT)-fed leaves compared to control ones under the same conditions. Hence photoinhibition caused by HI in bayberry was probably attributed to inactivation of PS2 RCs, and photoprotection from photodamage were mainly related to the xanthophyll cycle-dependent heat dissipation in excess photons. and Y.-P. Guo ... [et al.].
Four grapevine cultivars, i.e. Cabernet Sauvignon (a member of the Western Europe cultivar group), Rizamat (a member of the East cultivar group), Red Double Taste (a hybridized cultivar from Vitis vinifera L. and V. labrusca L.), and 1103Paulsen (a hybridized rootstock), were treated by three severity orders of drought stress for 25 d. Then net photosynthetic rate (PN), maximal photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPS2) of photosystem 2, total electron transport rate (JT), and electron transport flows used in carboxylation (JC) and in oxygenation (JO) reactions catalysed by ribulose-1,5-bisphosphate carboxylase/oxygenase were determined. PN was determined again after re-watering for 2 d by gas exchange measurement. Along with the increase in severity of drought stress, PN, Fv/Fm, ΦPS2, JT, and JC in all four cultivars decreased. The range of decrease differed among cultivars. JO expressed various trends from cultivar to cultivar. In Rizamat that received slight and moderate drought stress, PN evidently decreased, but JO markedly increased, thus maintaining high values of JT and ΦPS2. Prior to the moderate drought stress, the Fv/Fm was high in Rizamat, indicating that the photodamage had not happened ahead of the moderate drought stress given. Under the severe drought stress, the photorespiration rate in Rizamat decreased by 70 %, and JT, ΦPS2, and Fv/Fm also dropped to very low values, i.e. the photodamage of photosynthetic apparatus has taken place. This suggested that the photorespiration has consumed the excessive assimilatory power and the photo-protective function of photorespiration is very important for Rizamat. When Cabernet Sauvignon grew under drought stress, its JO decreased in a small range, thus maintaining higher values of JC, JT, ΦPS2, and Fv/Fm; hence no serious photodamage occurred. Despite of the fact that PN of cv. Red Double Taste decreased markedly under the slight drought stress, JO still increased under the severe drought stress. This suggests that photorespiration is important in photoprotection under drought stress. JO in cv. 1103Paulsen markedly decreased under slight stress. Accordingly, PN, Fv/Fm, ΦPS2, JT, and JC decreased to extremely low values. Thus photorespiration effectively protects the photosynthetic apparatus from photo-damage under drought, assists in maintaining a relatively high ΦPS2, and helps PN to be rapidly recovered after re-watering. and X. Q. Guan ... [et al.].
Increase in both atmospheric CO2 concentration [CO2] and associated warming are likely to alter Earths' carbon balance and photosynthetic carbon fixation of dominant plant species in a given biome. An experiment was conducted in sunlit, controlled environment chambers to determine effects of atmospheric [CO2] and temperature on net photosynthetic rate (P N) and fluorescence (F) in response to internal CO2 concentration (C i) and photosynthetically active radiation (PAR) of the C4 species, big bluestem (Andropogon gerardii Vitman). Ten treatments were comprised of two [CO2] of 360 (ambient, AC) and 720 (elevated, EC) µmol mol-1 and five day/night temperature of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Treatments were imposed from 15 d after sowing (DAS) through 130 DAS. Both F-P N/Ci and F-P N/PAR response curves were measured on top most fully expanded leaves between 55 and 75 DAS. Plants grown in EC exhibited significantly higher CO2-saturated net photosynthesis (Psat), phosphoenolpyruvate carboxylase (PEPC) efficiency, and electron transport rate (ETR). At a given [CO2], increase in temperature increased P sat, PEPC efficiency, and ETR. Plants grown at EC did not differ for dark respiration rate (RD), but had significantly higher maximum photosynthesis (P max) than plants grown in AC. Increase in temperature increased Pmax, RD, and ETR, irrespective of the [CO2]. The ability of PEPC, ribulose-1,5-bisphosphate carboxylase/oxygenase, and photosystem components, derived from response curves to tolerate higher temperatures (>35 °C), particularly under EC, indicates the ability of C4 species to sustain photosynthetic capacity in future climates. and V. G. Kakani, G. K. Surabhi, K. R. Reddy.
The effects of shade on the growth, leaf photosynthetic characteristics, and chlorophyll (Chl) fluorescence parameters of Lycoris radiata var. radiata were determined under differing irradiances (15, 65, and 100% of full irradiance) within pots. The HI plants exhibited a typical decline in net photosynthetic rate (PN) during midday, which was not observed in MI- and LI plants. This indicated a possible photoinhibition in HI plants as the ratio of variable to maximum fluorescence (Fv/Fm) value was higher and the minimal fluorescence (F0) was lower in the, and LI plants. Diurnal patterns of stomatal conductance (gs) and transpiration rate (E) were remarkably similar to those of PN at each shade treatments, and the intercellular CO2 concentration (Ci) had the opposite change trend. Under both shading conditions, the light saturation point, light compensation point and photon-saturated photosynthetic rate (Pmax) became lower than those under full sunlight, and it was the opposite for the apparent quantum yield (AQY). The higher the level of shade, the lower the integrated daytime carbon gain, stomatal and epidermis cell densities, specific leaf mass (SLM), bulb mass ratio (BMR), leaf thickness, and Chl a/b ratio. In contrast, contents of Chls per dry mass (DM), leaf area ratio (LAR), leaf mass ratio (LMR), leaf length, leaf area and total leaf area per plant increased under the same shade levels to promote photon absorption and to compensate for the lower radiant energy. Therefore, when the integrated daytime carbon gain, leaf area and total leaf area per plant, which are the main factors determining the productivity of L. radiata var. radiata plant, were taken into account together, this species may be cultivated at about 60-70% of ambient irradiance to promote its growth. and S. B. Zhou ... [[et al.].
The responses to irradiance of photosynthetic CO2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd). Net photosynthetic rate (PN) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (μmol m-2 s-1, while the PS2 non-cyclic electron transport (P-rate) showed a maximum at PPFD 800 μmol m-2 s-1. With PPFD increasing, either leaf potential photosynthetic CO2 assimilation activity (Fd/Fs) and PS2 maximal photochemical activity (Fv/Fm) decreased or the ratio of the inactive PS2 reaction centres (RC) [(Fi - Fo)/(Fm - Fo)] and the slow relaxing non-photochemical Chl fluorescence quenching (qs) increased from PPFD 1 200 μmol m-2 s-1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(Fs - Fo')/Fm' - Fo')], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (qf and qm) increased remarkably from PPFD 900 (μmol m-2 s-1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 μmol m-2 s-1 and photoinhibition occurred above PPFD 900 μmol m-2 s-1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 μmol m-2 s-1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 μmol m-2 s-1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter PN and the Chl fluorescence parameter Fv/Fm as a definition of saturation irradiance and photoinhibition of plant leaves. and Husen Jia, Dequan Li.
The effect of heat stress (35 to 50 °C) on photosynthesis was investigated in heat tolerant (N 22) and heat sensitive (IR 8) cultivars of rice {Oryza sativa L.). The net photosynthetic rate showed greater thermal stability in N 22 than in IR 8. The relative dechne of the rate of whole chain electron transport and photosystem 2 (PS2) activity was more pronounced in IR 8 than N 22. In both cultivars photosystem (PSI) activity was stimulated by thermal treatment. Chlorophyll (Chl) a fluorescence transient arising ffom PS2 showed inhibition in both cultivars at 45 and 50 °C. Maximum fluorescence decreased more in IR 8 than in N 22 by high temperature treatment.
The effect of high irradiance (HI) during desiccation and subsequent rehydration of the homoiochlorophyllous desiccation-tolerant shade plant Haberlea rhodopensis was investigated. Plants were irradiated with a high quantum fluence rate (HI; 350 µmol m-2 s-1 compared to ca. 30 µmol m-2 s-1 at the natural rock habitat below trees) and subjected either to fast desiccation (tufts dehydrated with naturally occurring thin soil layers) or slow desiccation (tufts planted in pots in peat-soil dehydrated by withholding irrigation). Leaf water content was 5 % of the control after 4 d of fast and 19 d of slow desiccation. Haberlea was very sensitive to HI under all conditions. After 19 d at HI, even in well-watered plants there was a strong reduction of rates of net photosynthesis and transpiration, contents of chlorophyll (Chl) and carotenoids, as well as photosystem 2 activity (detected by the Chl fluorescence ratio RFd). Simultaneously, the blue/red and green/red fluorescence ratios increased considerably suggesting increased synthesis of polyphenolic compounds. Desiccation of plants in HI induced irreversible changes in the photosynthetic apparatus and leaves did not recover after rehydration regardless of fast or slow desiccation. Only young leaves survived desiccation. and K. Georgieva, S. Lenk, C. Buschmann.
Wheat (Triticum aestivum L.) cv. Jimai22 was used to evaluate the effect of ethylene evolution rate (EER) and 1-aminocyclopropane-1-carboxylic acid (ACC) and their relations with photosynthesis and photochemical efficiency in plants well-watered (WW) and under a severe water deficit (SWD). SWD caused a noticeable reduction in the grain mass. The marked increases in both EER and the ACC concentration were observed under SWD; it was reversed effectively by exogenous spermidine (Spd) or amino-ethoxyvinylglycine (AVG). Thermal images indicated that SWD increased obviously the temperature of flag leaves, mainly due to the decrease in transpiration rate under SWD. Exogenous Spd or AVG decreased to some extent the temperature of the flag leaves. The strong decline in photosynthetic rate (PN) and stomatal conductance as well as the photodamage of PSII were also observed under SWD after 14 and 21 days after anthesis (DAA). Intercellular CO2 concentration was reduced at 7 DAA, but slightly increased at 14 and 21 DAA under SWD, indicating that the decreased PN at 7 DAA might result from stomatal limitations, while the decline after 14 and 21 DAA might be attributed to nonstomatal limitations. Correlation analysis suggested that EER and ACC showed negative relations to photosynthesis and photochemical efficiency. Data obtained suggested that the effects of SWD were mediated predominantly by the increase in EER and ACC concentration, which greatly decreased the leaf photosynthesis and photochemical efficiency, and, therefore, reduced the grain mass. Application of Spd or AVG reduced the EER and ACC, and thus positively influenced photosynthesis and photochemical efficiency under SWD., W. Yang, Y. Yin, W. Jiang, D. Peng, D. Yang, Y. Cui, Z. Wang., and Obsahuje bibliografii