Cations such as Mg2+ regulate spillover of absorbed excitation energy mainly in favour of photosystem (PS) 2. Effect of low concentration (<10 mM) of the monovalent cation Na+ on chlorophyll (Chl) a fluorescence was completely overridden by divalent cation Mg2+ (5 mM). Based on Chl a fluorescence yield and 77 K emission measurements, we revealed the role and effectiveness of anions (Cl-, SO42-, PO43-) in lowering the Mg2+-induced PS2 fluorescence. The higher the valency of the anion, the lesser was the expression of Mg2+ effect. Anions may thus overcome Mg2+ effects up to certain extent in a valency dependent manner, thereby diverting more energy to PS1 even in the presence of MgCl2. They may do so by reversing Mg2+-induced changes. and Anjana Jajoo, Sudhakar Bharti.
Effects of benzyladenine (BA) and abscisic acid (ABA) applied separately or simultaneously on parameters of gas exchange of Phaseolus vulgaris L. leaves were studied. In the first two experimental sets) 100 μM ABA and 10 μM BA were applied to plants sufficiently supplied with water. Spraying of leaves with ABA decreased stomatal conductance (gs) and in consequence transpiration rate (E) and net photosynthetic rate (PN) already 1 h after application, but 24 h after application the effect almost disappeared. 10 μM BA slightly decreased gas exchange parameters, but in simultaneous application with ABA reversed the effect of ABA. Immersion of roots into the same solutions markedly decreased gas exchange parameters and 24 h after ABA application the stomata were completely closed. The effect of ABA was ameliorated by simultaneous BA application, particularly after 1-h treatment. In the third experimental set, plants were pre-treated by immersing roots into water, 1 μM BA, or 100 μM ABA for 24 h and then the halves of split root system were dipped into different combinations of 1 μM BA, 100 μM ABA, and water. In plants pre-treated with ABA all gas exchange parameters were small and they did not differ in plants treated with H2O+H2O, H2O+BA, or BA+BA. In plants pre-treated with BA or H2O, markedly lower values of PN were found when both halves of roots were immersed in ABA. Further, the effects of pre-treatment of plants with water, 1 μM BA, 100 μM ABA, or ABA+BA on the development of water stress induced by cessation of watering and on the recovery after rehydration were followed. ABA markedly decreased gas exchange parameters at the beginning of the experiment, but in its later phase the effect was compensated by delay in development of water stress. BA also delayed development of water stress and increased PN in water-stressed leaves. BA reversed the effect of ABA at mild water stress. Positive effects of BA and ABA pre-treatments were observed also after rehydration.
Two types of photosystem 2-light-harvesting complex 2 (PS2-LHC2) supercomplexes with similar pigment and protein composition were isolated directly from thylakoid membranes by sucrose density gradient centrifugation. Electron microscopy and single particle image analysis revealed the first Type as single unpaired PS2-LHC2 supercomplexes, whereas the second Type was characterized as pairs of two PS2-LHC2 supercomplexes attached together by their stromal sides. Unstacking of thylakoid membranes resulted in a spontaneous disintegration of the paired supercomplexes into single unpaired particles. A model of the organisation of the pigment-protein complexes in grana region is proposed. and L. Bumba, M. Hušák, F. Vácha.
Environmental stresses, such as cold, heat, salinity, and drought, induce ethylene production and oxidative stress and cause damage in plants. On the other hand, studies have shown that salicylic acid (SA) induced resistance to environmental stresses in plants. In this research, the effects of ethylene on chlorophyll (Chl), carotenoid (Car), anthocyanin, flavonoids, ascorbic acid, dehydroascorbic acid, total ascorbate, lipid peroxidation, and ethylene production in leaves of canola pretreated with SA were studied. The plants were grown in pots until they have four leaves. Leaves were sprayed for two days with three different concentrations of SA (0, 0.5, and 1 mM). The plants were treated for three days with three concentrations of ethylene (0, 50, and 100 ppm). At the end of the ethylene treatments, all examined parameters were measured. The results showed that the ethylene treatments induced lipid peroxidation, while SA mitigated this effect. The ethylene treatment lowered significantly Chl and Car contents and anthocyanin accumulation, but SA alleviated these effects. SA induced an increase in ascorbic acid content in canola plants after the ethylene treatments. Therefore, we concluded that SA played an important role in the alleviation of damages caused by stress conditions. and M. M. Tirani, F. Nasibi, Kh. M. Kalantari.
Watermelon (Citrillus lanatus) plants were grown for two consecutive years in open-top chambers with three different ozone concentrations (O3-free air, O3 ambient, and air with additional O3; CFA, NFA, and NFA+O3) and three nitrogen fertilizer concentrations [0, 14.0, and 29.6 g N per pot; N0, N1, and N2). There was an interaction between ozone and N fertilizer for the major parameters studied. O3 and N2 treatments led to a significant decrease in maximum efficiency of photosystem 2 (PS2) photochemistry (Fv/Fm), and induced a significant decrease in the actual quantum yield of PS2 (ΦPS2), due mainly to the increased closure of PS2 reaction centres (qP) and to an increase in the non-photochemical quenching (NPQ). On the other hand, these plants exhibited an increased susceptibility to photoinhibition, which could be associated with an increased fraction of reduced QA. An increase in lipid peroxidation indicated that damage was occurring at the membrane levels. High N concentration enhanced the detrimental effects of ozone on the fluorescence parameter induction and lipid peroxidation. All these negative alterations led to a decreased yield. and A. Calatayud, F. Pomares, E. Barreno.
The review summarizes results concerning photosynthetic systems with chlorophylls and carotenoids obtained by means of spectral methods such as polarized radiation, photoacoustic spectroscopy, delayed luminescence, thermal deactivation, and leading to construction of model systems. and D. Frąckowiak, B. Smyk.
In aqueous solutions of chlorophyll (Chl) a with synthesized polypeptides, at high ratios of Chl to polypeptides (about 75-150 µM to 500 µM) clusters of polypeptides and pigment molecules were formed. The main absorption maxima of more than one formed cluster were located at about 500 nm (Soret band) and in the region of 720-806 nm (red band). The formation of these clusters was fairly slow (some hours) at room temperature and even slower at 4 °C. The rate of cluster formation increased with the increase in Chl concentration. The addition of the even low amount of reaction centres (RCs), separated from the purple bacteria Rhodobacter sphaeroides, to the sample of Chl with polypeptides caused a very strong decrease in the efficiency of cluster formation, and a change in concentration ratios of various pigment-polypeptide aggregates. It was probably a competition between the interaction of Chl with polypeptides and with the RCs. The yield of thermal deactivation of the clusters was high, much higher than that for the RCs alone and it was different for various types of cluster. The clusters absorbing at 725-750 nm were fluorescent with maximum of emission at about 770 nm, whereas clusters absorbing at about 800 nm were nonfluorescent. and H. Enomoto ... [et al.].
The effect of CO2 increase on gas exchange and water-use effíciency (WUE) in three temperate deciduous species (Fagus crenata, Ginkgo biloba and Alnus firma) under gradually-developing drought-stress was assessed. Seedlings were grown within transparent open-top cabinets and maintained for 4 monťhs at mean CO2 concentrations of either 350 (ambient; C350) or 700 pmol moT’ (elevated; C700) and combined with five water regimes [leaf water potential, higher than -0.3 (well- watered), -0.5 and -0.8 (moderate drought), -1.0 and lower than -1.2 MPa (serious drought-stress)]. Increase in CO2 concentration induced a 60 % average increase in net photosynthetic rate (P^) under well-watered conditions. The effect of C700 became more pronounced with drought stress established, with an 80 % average increase in at as low as -0.8 MPa; leaf conductance to water vapour transfer (gs) and transpiration rate (£), however, were significantly decreased. Consequently, WUE increased under drought, through drought stress affected potential E sooner than potential P^. The interaction of CO2 x drought stress on WUE was significant in that Pn was stimulated while E in C700 enriched plants resembled that of C350 plants under drought. Hence if a doubling of atmospheric CO2 concentration occurs by the mid 2U* century, then greater P^ in F. crenata, G. biloba and^. firma may be expected and the drought susceptibility of these species will be substantially enhanced.
Response of net photosynthetic rate (PN), stomatal conductance
(gs), intercellular CO2 concentration (ci), and photosynthetic efficiency (Fv/Fm) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C800) or 380 (C380) µmol mol-1 CO2 concentration under sufficient water supply or under water stress. The well-watered plants at C800 showed a 2.2 fold enhancement of PN without any change in gs. Under both C800 and C380, water stress decreased PN and gs significantly without any substantial reduction of ci, suggesting that both stomatal and non-stomatal factors regulated PN. However, the photosynthetic efficiency of PS2 was not altered.
The interactive effects of NO3 fertilization and salinity levels on leaf CO2 fixation, the dry matter accumulation, the proline and sugar contents in tomato shoots were determined in a greenhouse experiment using a well-controlled aerohydroponic systém. Under high salinity levels, increasing N fertilization from 5 mM NO3 up to 20 mM NO3 was ineffective in countering adverse effects of growth. Photosynthesis was inhibited as a result of both osmotic and specific ion effects. The high šalině concentrations stimulated the sugar accumulation in leaves, whereas the proline accumulation was primarily induced by increased NO3 levels.