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.
Under natural conditions we found a significant variation in oxygen evolution rate (OER) in flag leaves of different rice genotypes during the grain filling stage. Cv. Roxinho showed the highest OER [42 µmol(O2) m-2 s-1], followed by BRS Taim, BRS Pelota, BRS Bojuru, IR58025B, BRS 6 Chui, and BR-IRGA 409, with 37.0, 34.0, 33.0, 31.8, 29.0, 28.0, and 27.6 µmol(O2) m-2 s-1, respectively. The lack of fertility in the male-sterile rice line IR58025A prolonged the photosynthetic capacity by at least 15 d when compared to the normal fertility found in the IR58025B line. No difference was observed in OER among first (flag) and second leaves in both IR58025A and IR58025B rice lines. and M. A. Bacarin ... [et al.].
A synthesized version of the dioxygen chemistry is reviewed. Since superoxide, hydrogen peroxide and hydroxyl radicals are products of the dioxygen reduction, a Chemical characterization is advanced. In addition, Fe, Mn and Cu integrated in enzymes cormected with reduction products of oxygen in plants aie chemically characterized. An overview of the oxygen metaboiism in photosynthesis follows. Accordingly, the production of triplet oxygen through the water-splitting complex as well as the production and control of singlet oxygen and hydrogen peroxide in the photosystem 2 are evaluated. Furthermore, the superoxide and hydrogen peroxide production and control in photosystem 1 are evaluated. The chloroplast oxy-radicals production under stress conditions, mainly an interaction between zeaxanthin and singlet oxygen under photoinhibitory conditions, as well as the interactions between sulphin dioxide and superoxide are given. Furthermore, the effects of low temperatmes on the oxygen metaboiism as well as the nutritional effects of Mn, Fe and Cu on the oxy-radicals production and control are evaluated.
Photosynthesis, as a fundamental element in the life process, is integrated in the evolution of living systems on the basis of hydrogen cycles on various hierarchic levels. Conversion of radiant energy enables the oxidation of water, whereby free oxygen accumulates in the atmosphere. Hydrogen is (reversibly) stored in organic materials formed under reductive CO2-fixation and by the incorporation of the other elements, which are necessary for living systems. All endergonic processes in living cells are finally driven by the energy released through the clean recombination of protons and electrons with oxygen to water. Duration of the stored energy and the complexity of the systems thus produced is correlated negatively with the conversion efficiency of the radiation energy. Entropy is a unifying principle in the evolution of living systems, inclusive human societies.
The effect of ethylenediurea (EDU) was tested using the chlorophyll (Chl) a fluorescence transient analysis, performed with JIP-test, to assess ambient ozone (O3) effects on photosynthesis of adult trees under natural conditions. Twelve adult European ash (Fraxinus excelsior L.) trees, known to be sensitive or tolerant to O3, determined by presence symptomatic (S) or absence asymptomatic (AS) trees of foliar symptoms in previous years, were treated either with distilled water containing 450 g m-3 EDU or with distilled water. Once a month across the growing season [the accumulated exposure over a threshold of 40 nmol(O3) mol-1 was 32.49 µmol mol-1 h-1], Chl a fluorescence transients were measured in vivo on dark-adapted leaves of 1-year-old labeled shoots, from the lower crown part. Twenty-five parameters were calculated. The maximum quantum yield of primary photochemistry (ϕPo or Fv/Fm) did not differentiate between S-and AS-trees, while increased Chl content and de-excitation rates suggested compensation of O3 injury in S-trees. Seasonal reductions in absorbing fluxes and increase in heat and fluorescence dissipation processes was due to leaf ageing and drought, the latter suggesting water deficit influenced Chl a fluorescence stronger than ambient O3 exposure. AS-trees showed elevated probability of connectivity among photosystem 2 units, a mechanism to stimulate energy dissipation and reduce photo-oxidative injury. EDU prevented the inactivation of reaction centers. This slight effect does not warrant EDU as a tool to assess O3 effects on photosynthesis, while the JIP-test is suggested for a quantitative assessment in adult trees. and N. Contran ... [et al.].
Ozone (O3) is important air pollutant inducing severe losses of horticultural production. Cultivars of the same species, but with different leaf colors, may differ in their ozone sensitivity. However, it has not been clarified yet if different leaf coloration influences such a sensitivity. In this study, two purple-leafed and two green-leafed cultivars of Pakchoi were selected for ozone fumigation (240 ± 20 nmol mol-1, 09:00-16:00 h). Elevated O₃ decreased chlorophyll content, increased anthocyanin (Ant) content, damaged cell membrane integrity, enhanced antioxidative enzyme activities, depressed photosynthetic rate (PN) and stomatal conductance (gs), inhibited maximal quantum yield (Fv/Fm) and effective quantum yield [YII] of PSII photochemistry, and caused visible injury. Purple-leafed cultivars with higher Ant contents were more tolerant than green-leafed cultivars as indicated by lower relative enhancement in malondialdehyde content and lower relative losses in PN, gs, Fv/Fm, and YII. The higher ability to synthesize Ant in the purple-leafed cultivars contributed to their higher photoprotective ability., L. Zhang, S. Xiao, Y. J. Chen, H. Xu, Y. G. Li, Y. W. Zhang, F. S. Luan., and Obsahuje bibliografii
The use and degradation of radiant energy in water-stressed wheat (Triticum durum Desf. ssp. enduró) was examined by the fluorescence quenching, absorbance changes around 830 nm due to P700 oxidation, and the gas exchange parameters. Under water stress, P700 accumulated in the photochemically inactive oxidised form especially at a high irradiance.
Our experiment was conducted in order to find out effects of paclobutrazol (PBZ; 30 μl l-1) on morphology, photosynthetic process, and stress markers under water surplus and deficit conditions in several wheat genotypes. Study revealed that relative water content (RWC), photosynthetic rate, and maximal quantum yield of PSII (FV/FM) was improved after a PBZ application both under irrigation and water deficit across the genotypes, while the stomatal conductance was reduced. Further, the application of PBZ led to reduced leaf area in wheat genotypes. Moreover, a proline content was higher in the wheat genotypes under water stress as compared to the irrigated plants. The application of PBZ led to downregulation of the proline content under water deficit, while there was no significant change in the content and activity under irrigation with or without the PBZ treatment. These findings indicated that due to the application of PBZ the wheat genotypes might sense a lower stress level (indicated by the proline content) and better drought tolerance (according to RWC and photosynthetic characteristics)., S. K. Dwivedi, Ajay Arora, S. Kumar., and Obsahuje bibliografii