We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψw) and leaf osmotic potential (Ψs) decreased. Leaf Ψw was at least -0.32 MPa lower than the Ψw of solution. Na+ and K+ ions explained about 78 % of decrease in Ψs. K+ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely, Na+ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate
(PN) and stomatal conductance (gs) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO2 concentration (Ci) followed the same trend. The PN as a function of Ci showed that both the initial linear slope and upper plateau of the PN vs. Ci curve were markedly affected by high salinity (40 and 55 ‰). and N. Suárez, E. Medina.
Shading of the tubular photobioreactor (PBR) surfaces that diminished solar irradiance to 70 % led to higher biomass productivity and greater accumulation of total chlorophyll and carotenoids compared to the values obtained when the PBR was completely exposed to full sunlight. and C. U. Ugwu, H. Aoyagi.
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 ΦPS2, 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. and E. Nuñez-Olivera ... [et al.].
Chlorophyll (Chl) a and Chl b absorbances were determined in extracts from leaves of Citrus aurantium L. using the solvents diethyl ether (100 %), buffered 80 % aqueous acetone, and N,N'-dimethyl formamide (DMF) (99.83 %). The respective standard deviations (σ) and coefficients of variability (CV) were used to establish the errors obtained when using impure solvents. Buffered 80 % aqueous acetone gave an error of 2.1 % for Chl a and 7.1 % for Chl b, while DMF gave errors of 3.5 and 6.7 %, respectively. For current Chl determination we propose a non-abrasive method, which extracts 15 leaf discs (diameter 6 mm) with 10 cm3 of buffered 80 % aqueous acetone or DMF in hermetically sealed flasks during 24 h in darkness at 4 °C. and A. L. García, N. Nicolás.
The steady-state oxygen evolution rate was previously shown to be stimulated by the disaccharide trehalose in PSII suspension. Here we showed a similar increase in the rate of oxygen evolution in PSII core complexes from spinach in solution and in proteoliposomes in the presence of trehalose. Using direct electrometrical technique, we also revealed that trehalose had no effect on the kinetics of electron transfer from Mn to redox-active-tyrosyl radical, YZ (S1 - S2 transition), while it accelerated the kinetics of electrogenic proton transport during S2 - S3 and S4 - S0 transitions of the wateroxidizing complex (WOC) induced by the first, second, and third laser flashes in dark-adapted PSII samples. These observations imply that the effect of trehalose occurrs due to its interaction with the WOC., M. D. Mamedov, E. S. Nosikova, L. A. Vitukhnovskaya, A. A. Zaspa, A. Yu. Semenov., and Obsahuje bibliografické odkazy
Photosynthetic activity of leaf disks from chlortoluron (2 µmol per plant) treated and non-treated non-transgenic and transgenic (PGF-6) tobacco plants was measured from 1 up to 21 d after treatment under greenhouse conditions. PGF-6 plants, expressing the fused rat cytochrome P4501A1/yeast reductase genes were used. PGF-6 plants were much more chlortoluron-resistant than control plants. In non-transgenic tobacco plants the electron transport flow to PQ pool was strongly inhibited 1 d after treatment with herbicide whereas it was still existing in PGF-6 plants although some reduction was observed. The quantum yield of photosystem 2 (ΦPS2) which is related to the quantum yield of whole-chain electron transfer was much more inhibited by chlortoluron than the primary PS2 photochemistry, measured by the ratio Fv/Fm. Lower PS2 activity was found for herbicide-treated non-transgenic plants up to the 9th day. Then it started to increase in both control and PGF-6 plants, but more rapidly in PGF-6 ones, and its values were near to the control level at the 21st d after chlortoluron treatment. and E. Yordanova ... [et al.].
The effect of water on the primary photosynthetic activity of purple bacterium Rhodospirillum rubrum was studied in Hexadecane-Tween-Spane (HTS)- and phospholipid (PLC)-reverse micelles. Reverse micelles offer the possibility of modulating the amount of water to which enzymes and multienzymatic complexes are exposed. Fast bacteriochlorophyll (BChl) fluorescence induction kinetics and reaction centre absorption changes at 820 nm were used as an assay for the functional transfer of bacterial cells into HTS-reverse micelles and bacterial photosynthetic complexes (BPC) into PLC-reverse micelles. Both the bacterial cells and BPC showed an increase in the rate of primary photosynthetic activity by increasing the concentration of water in the reverse micelles. The bacterial cells could be kept viable for many hours in HTS-reverse micelles in presence of 6% (v/v) water. NMR studies indicated that the photosynthetic activity was affected by the availability of water in reverse micelles. The bacterial cells in HTS or BPC in PLC reverse micelles could be used to further understand the influence of water on the organisation and function of photosynthetic complexes. and A. Srivastava, A. Darszon, R. J. Strasser.
The combined effects of water stress (WS) and low irradiance (LI) on growth, photosynthesis, osmotic adjustment, and lipid peroxidation were studied in dragon spruce (Picea asperata Mast.) seedlings grown under two water treatments (well watered, 100 % of field capacity, and water stressed, 30 % of field capacity) and two irradiances (HI, 100 % of full sunlight and LI, 15 % of full sunlight). WS reduced growth, chlorophyll (Chl) a and b contents, net photosynthetic rate, transpiration rate, stomatal conductance, and effective quantum yield of photosystem 2 (Y) but increased free proline and malondialdehyde contents. LI increased Chl contents and decreased Y, photochemical quenching (qP), and non-photochemical quenching (qN) under both water treatments. Hence the seedlings in the understory were more sensitive to drought than to LI. and Y. Yang ... [et al.].
A gradual reduction in leaf water potential (Ψleaf), net photosynthetic rate (PN), stomatal conductance, and transpiration rate was observed in two drought tolerant (C 306 and K 8027) and two susceptible (RW 893 and 899) genotypes subjected to water stress. The extent of reduction was lower in K 8027 and C 306 and higher in RW 893 and RW 899. Rewatering the plants after 5 d of stress restored PN and other gas exchange traits in all four cultivars. Water stress had no significant effect on variable to maximum fluorescence ratio (Fv/Fm) indicating that water stress had no effect on primary photochemistry of photosystem 2 (PS2). However, water stress reduced the efficiency of excitation energy transfer (F'v/F'm) and the quantum yield of electron transport (ΦPS2). The reduction was more pronounced in susceptible cultivars. Water stress had no significant effect on photochemical quenching, however, the non-photochemical quenching increased by water stress. and D. Subrahmanyam ... [et al.].