The effects of elevated growth temperature (ambient + 3.5°C) and CO2 (700 μmol mol-1) on leaf photosynthesis, pigments and chlorophyll fluorescence of a boreal perennial grass (Phalaris arundinacea L.) under different water regimes (well watered to water shortage) were investigated. Layer-specific measurements were conducted on the top (younger leaf) and low (older leaf) canopy positions of the plants after anthesis. During the early development stages, elevated temperature enhanced the maximum rate of photosynthesis (Pmax) of the top layer leaves and the aboveground biomass, which resulted in earlier senescence and lower photosynthesis and biomass at the later periods. At the stage of plant maturity, the content of chlorophyll (Chl), leaf nitrogen (NL), and light response of effective photochemical efficiency (ΦPSII) and electron transport rate (ETR) was significantly lower under elevated temperature than ambient temperature in leaves at both layers. CO2 enrichment enhanced the photosynthesis but led to a decline of NL and Chl content, as well as lower fluorescence parameters of ΦPSII and ETR in leaves at both layers. In addition, the down-regulation by CO2 elevation was significant at the low canopy position. Regardless of climate treatment, the water shortage had a strongly negative effect on the photosynthesis, biomass growth, and fluorescence parameters, particularly in the leaves from the low canopy position. Elevated temperature exacerbated the impact of water shortage, while CO2 enrichment slightly alleviated the drought-induced adverse effects on P max. We suggest that the light response of ΦPSII and ETR, being more sensitive to leaf-age classes, reflect the photosynthetic responses to climatic treatments and drought stress better than the fluorescence parameters under dark adaptation. and Z.-M. Ge ... [et al.].
Chlorophyll fluorescence parameters (Fv/Fm, RFd) of nine bryophyte and one lichen species were investigated after prolonged exposure to elevated UV-B radiation. The majority of the investigated bryophytes showed a prompt or inducible tolerance to increase UV-B irradiation. Among the investigated species high degree of UV-tolerance coincides with strong desiccation tolerance. and Z. Csintalan ... [et al.].
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.
Ultrastructural and physiological effects of exposure to 1 ppm and 5 ppm of cadmium (Cd) on cultured cells of Koliella antarctica, a green microalga from Antarctica, were investigated. The amount of Cd in the alga rose with the increase of the metal concentration in the growth medium and most Cd remained outside the cells, bound to the components of the cell walls. The increase of Cd in the microalga was concomitant with the decrease of other elements, mainly calcium (Ca). Exposure to 1 ppm Cd slowed culture growth by inhibiting cell division and also caused the development of some misshapen cells with chloroplast showing disordered thylakoids. However, this concentration did not substantially affect the chlorophyll (Chl) content or photosystem (PS) activity. At 5 ppm, Cd cell growth suddenly stopped and some cells lysed. After a week of Cd contamination, the cells were enlarged and severely damaged. The chloroplasts showed great ultrastructural alterations and a reduced Chl content. Cd exposure negatively affected PSII, whose activity was almost completely lost after four days. and N. La Rocca ... [et al.].
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.
The gas exchange, parameters of chlorophyll fluorescence, contents of pigments, and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), as well as lipid peroxidation were investigated in two field-grown coffee species, Coffea arabica and C. liberica, exposed to drought and re-hydration. Drought caused a more pronounced inhibition of net photosynthetic rate in C. liberica compared to C. arabica. The de-epoxidation of xanthophyll cycle pigments at midday estimated by leaf reflectance was much higher in C. arabica than in C. liberica, but no significant change was found in response to drought. Under moderate drought, the activities of SOD and APX increased significantly only in C. arabica. The maximum photochemical efficiency of photosystem 2, PS2 (Fv/Fm) at predawn did not change and there was no lipid peroxidation during this time. Under severe drought Fv/Fm decreased and initial fluorescence (F0) increased for both species, and SOD activity increased, APX activity remained relatively high, and malondialdehyde (MDA) accumulated in C. arabica, while APX decreased in C. liberica. The photosynthetic apparatus of C. arabica was completely recovered after 5 d of re-irrigation as indicated by the restoration of Fv/Fm to the control values. A lack of recovery upon rewatering of C. liberica indicated irreversible damage to PS2. Hence compared to C. liberica, C. arabica possesses a higher desiccation-induced antioxidative protection and higher portion of the total pigment pool used in photoprotection, which might aid alleviating photoinhibitory damage during desiccation and photosynthesis recovery when favourable conditions are restored. and Z.-Q. Cai ... [et al.].
The aim of this study was to assess the impact of the mitochondrial alternative oxidase (AOX) pathway on energy metabolism in chloroplasts, and evaluate the importance of the AOX in alleviating drought-induced photoinhibition in pepper (Capsicum annuum L.). Inhibition of AOX pathway decreased photosynthesis and increased thermal energy dissipation in plants under normal conditions. It indicated that AOX pathway could influence chloroplast energy metabolism. Drought reduced carbon assimilation. Photoinhibition was caused by excess of absorbed light energy in spite of the increase of thermal energy dissipation and cyclic electron flow around PSI (CEF-PSI). Upregulation of AOX pathway in leaves experiencing drought would play a critical role in protection against photoinhibition by optimization of carbon assimilation and PSII function, which would avoid over-reduction of photosynthetic electron transport chain. However, inhibition of AOX pathway could be compensated by increasing the thermal energy dissipation and CEF-PSI under drought stress, and the compensation of CEF-PSI was especially significant., W. H. Hu, X. H. Yan, Y. He, X. L. Ye., and Obsahuje bibliografii
The protective role of light-harvesting complex 2 (LHC2) dissociation from photosystem 2 (PS2) complex was explored by the 5'-p-fluorosulfonylbenzoyl adenosine (FSBA, an inhibitor of protein kinase) treatment at saturating irradiance (SI) in soybean leaves and thylakoids. The dissociation of some LHC2s from PS2 complex occurred after SI treatment, but FSBA treatment inhibited the dissociation as demonstrated by analysis of sucrose density gradient centrifugation of thylakoid preparation and low-temperature (77 K) chlorophyll (Chl) fluorescence. A significant increase in F0 and decrease in Fv/Fm occurred after SI, and the two parameters could largely recover to the levels of dark-adapted leaves after subsequent 3 h in the dark, but they could not recover in the FSBA-treated leaves at SI. Neither the electron transport activity of PS2 nor the D1 protein amount in vivo had significant change after SI without FSBA, whereas FSBA treatment at SI could result in significant decreases in both the PS2 electron transport activity and the D1 protein amount. When thylakoids instead of leaves were used, the PS2 electron transport activity and the D1 protein amount declined more after SI with FSBA than without FSBA. The phosphorylation level of PS2 core proteins increased, while the phosphorylation level of LHC2 proteins was reduced after SI. Also, the phosphorylation of PS2 core proteins could be greatly inhibited by the FSBA treatment at SI. Hence in soybean leaf the LHC2 dissociation is an effective strategy protecting PS2 reaction centres against over-excitation and photodamage by reducing the amount of photons transferred to the centres under SI, and the phosphorylation of PS2 core proteins plays an important role in the dissociation. and Hai-Bo Zhang, Da-Quan Xu.
Addition of nitrate to a suspension of NO3--depleted Chlorella vulgaris cells raised the O2-evolving capacity of the organism by 60%. The rate of O2-evolution under flash irradiation of the depleted cells was drastically reduced, which could be restored by addition of NO3-. The 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB)-insensitive O2-evolution, i.e., photosystem (PS) 2 activity of NO3--depleted cells, showed a 75% stimulation by addition of NO3-. PS1-mediated electron transport was also stimulated (50%) by addition of NO3-. Fluorescence yields of the NO3--depleted cells were significantly reduced. A normal fluorescence response was restored by the addition of NO3-. The fluorescence yield of the NO3--depleted and DCMU-treated-cells increased significantly after addition of NO3- ions, indicating a further reduction of the primary acceptor of PS2 (Q). In addition, the low temperature fluorescence emission spectra showed that energy transfer to PS2 and PS1 was much higher when nitrate was present. Hence nitrate accelerates the light-induced charge transfer from the intact O2-evolving system to the primary electron acceptor of PS2 and stimulates the PS1-mediated electron transport. and M. El-Anwar H. Osman, A. H. El-Naggar.
Carnivorous plants grow in nutrient-poor habitats and obtain substantial amount of nitrogen from prey. Specialization toward carnivory may decrease the ability to utilize soil-derived sources of nutrients in some species. However, no such information exists for pitcher plants of the genus Nepenthes, nor the effect of nutrient uptake via the roots on photosynthesis in carnivorous plants is known. The principal aim of present study was to investigate, whether improved soil nutrient status increases photosynthetic efficiency in prey-deprived pitcher plant Nepenthes talangensis. Gas exchange and chlorophyll (Chl) fluorescence were measured simultaneously and were correlated with Chl and nitrogen concentration as well as with stable carbon isotope abundance (δ13C) in control and fertilized N. talangensis plants. Net photosynthetic rate (PN) and maximum- (Fv/Fm) and effective quantum yield of photosystem II (ΦPSII) were greater in the plants supplied with nutrients. Biomass, leaf nitrogen, and Chl (a+b) also increased in fertilized plants. In contrast, δ13C did not differ significantly between treatments indicating that intercellular concentration of CO2 did not change. We can conclude that increased root nutrient uptake enhanced photosynthetic efficiency in prey-deprived N. talangensis plants. Thus, the roots of Nepenthes plants are functional and can obtain a substantial amount of nitrogen from the soil. and A. Pavlovič ... [et al.].