High level of phosphoenolpyruvate carboxylase (PEPC) gene was stably inherited and transferred from the male parent, PEPC transgenic rice, into a female parent, japonica rice cv. 9516. Relative to the female parent, the produced JAAS45 pollen lines exhibited high PEPC activity (17-fold increase) and also higher photosynthetic rates (about 36 %-fold increase). The JAAS45 pollen lines were more tolerant to photoinhibition and to photo-oxidative stress. Furthermore, JAAS45 pollen lines, as well as their male parent, were tested to exhibit a limiting C4 cycle by feeding with exogenous C4 primary products such as oxaloacetate (OAA). Thus the PEPC gene and photosynthetic characteristics of PEPC transgenic rice could be stably transferred to the hybrid progenies, which might open a new breeding approach to the integration of conventional hybridization and biological technology. and L. Ling, B. J. Zhang, D. M. Jiao.
Quercus ilex plants grown on two different substrates, sand soil (C) and compost (CG), were exposed to photosynthetic photon flux densities (PPFD) at 390 and 800 µmol(CO2) mol-1 (C390 and C800). At C800 both C and CG plants showed a significant increase of net photosynthetic rate (PN) and electron transport rate (ETR) in response to PPFD increase as compared to C390. In addition, at C800 lower non-photochemical quenching (NPQ) values were observed. The differences between C390 and C800 were related to PPFD. The higher PN and ETR and the lower dissipative processes found in CG plants at both CO2 concentrations as compared to C plants suggest that substrate influences significantly photosynthetic response of Q. ilex plants. Moreover, short-term exposures at elevated CO2 decreased nitrate photo-assimilation in leaves independently from substrate of growth. and C. Arena, L. Vitale, A. Virzo De Santo.
The photosynthetic responses to salt stress were examined in a wheat (Triticum aestivum L. cv. Asakaze)-barley (Hordeum vulgare L. cv. Manas) 7H addition line having elevated salt tolerance and compared to the parental wheat genotype. For this purpose, increasing NaCl concentrations up to 300 mM were applied and followed by a 7-day recovery period. Up to moderate salt stress (200 mM NaCl), forcible stomatal closure, parallel with a reduction in the net assimilation rate (PN), was only observed in wheat, but not in the 7H addition line or barley. Since the photosynthetic electron transport processes of wheat were not affected by NaCl, the impairment in PN could largely be accounted for the salt-induced decline in stomatal conductance (gs), accompanied by depressed intercellular CO2 concentration and carboxylation efficiency. Both, PN and nonstomatal limitation factors (Lns) were practically unaffected by moderate salt stress in barley and in the 7H addition line due to the sustained gs, which might be an efficient strategy to maintain the efficient photosynthetic activity and biomass production. At 300 mM NaCl, both PN and gs decreased significantly in all the genotypes, but the changes in PN and Lns in the 7H addition line were more favourable similar to those in wheat. The downregulation of photosynthetic electron transport processes around PSII, accompanied by increases in the quantum yield of regulated energy dissipation and of the donor side limitation of PSI without damage to PSII, was observed in the addition line and barley during severe stress. Incomplete recovery of PN was observed in the 7H addition line as a result of declined PSII activity probably caused by enhanced cyclic electron flow around PSI. These results suggest that the better photosynthetic tolerance to moderate salt stress of barley can be manifested in the 7H addition line which may be a suitable candidate for improving salt tolerance of wheat., D. Szopkó, É. Darkó, I. Molnár, K. Kruppa, B. Háló, A. Vojtkó,
M. Molnár-Láng, S. Dulai., and Obsahuje bibliografii
Saplings of the tropical trees Tibouchina pulchra (Cham.) Cogn., Caesalpinia echinata Lam., and Psidium guajava L. cv. Paluma were exposed in open-top chambers with charcoal filtered air and measurements of gas exchange and chlorophyll fluorescence were made before (t1) and after exposure to non-filtered air plus O3 (t2), simulating 6-h peaks of O3 similar to those observed in São Paulo city (SE Brazil, reaching an AOT40 of 641 nmol mol-1). After the fumigation, the net photosynthetic rate, stomatal conductance, transpiration rate, and Fv/Fm were reduced (p<0.05) for the three species. C. echinata was the most sensitive species and P. guajava cv. Paluma the most resistant. and R. M. Moraes ... [et al.].
Changes in fluorescence parameters observed during irradiation of the Scenedesmus cells showed that photosystem 2 (PS2) photoinactivation in cells treated with phenolic PS2 inhibitor 2-bromo-3-methyl-6-isopropyl-4-nitrophenol (BNT) was significantly accelerated in comparison with control and DCMU-treated cells. Moreover, a negligible difference in the rate of PS2 photoinactivation in the absence and presence of chloramphenicol indicated that both DCMU and BNT blocked the PS2 repair process.
Seedlings of winter rape were cultured in vitro on media containing 24-epibrassinolide, EBR (100 nM) and cadmium (300 µM). After 14 d of growth, fast fluorescence kinetics of chlorophyll (Chl) a and contents of photosynthetic pigments and Cd in cotyledons were measured. Cd was strongly accumulated but its content in cotyledons was 14.7 % smaller in the presence of EBR. Neither Cd nor EBR influenced the contents of Chl a and b and carotenoids. Cd lowered the specific energy fluxes per excited cross section (CS) of cotyledon. The number of active reaction centres (RC) of photosystem 2 (RC/CS) decreased by about 21.0 % and the transport of photosynthetic electrons (ET0/CS) by about 17.1 %. Simultaneously, under the influence of Cd, the activity of O2 evolving centres (OEC) diminished by about 19.5 % and energy dissipation (DI0/CS) increased by about 14.6 %. In the cotyledons of seedlings grown on media without Cd, EBR induced only a small increase in the activity of most photochemical reactions per CS. However, EBR strongly affected seedlings cultured with cadmium. Specific energy fluxes TR0/CS and ET0/CS of the cotyledons of plants Cd+EBR media were about 10.9 and 20.9 % higher, respectively, than values obtained for plants grown with Cd only. EBR also limited the increase of DI0/CS induced by Cd and simultaneously protected the complex of OEC against a decrease of activity. Hence EBR reduces the toxic effect of Cd on photochemical processes by diminishing the damage of photochemical RCs and OECs as well as maintaining efficient photosynthetic electron transport. and A. Janeczko ... [et al.].
The response of effective quantum yield of photosystem 2 (ΔF/Fm') to temperature was investigated under field conditions (1 950 m a.s.l.) in three alpine plant species with contrasting leaf temperature climates. The in situ temperature response did not follow an optimum curve but under saturating irradiances [PPFD >800 µìmol(photon) m-2s-1] highest ΔF/Fm' occurred at leaf temperatures below 10°C. This was comparable to the temperature response of antarctic vascular plants. Leaf temperatures between 0 and 15°C were the most frequently (41 to 56%) experienced by the investigated species. At these temperatures, ΔF/Fm' was highest in all species (data from all irradiation classes included) but the species differed in the temperature at which ΔF/Fm' dropped below 50% (Soldanella pusilla >20°C, Loiseleuria procumbens >25°C, and Saxifraga paniculata >40°C). The in situ response of ΔF/Fm' showed significantly higher ΔF/Fm' values at saturating PPFD for the species growing in full sunlight (S. paniculata and L. procumbens) than for S. pusilla growing under more moderate PPFD. The effect of increasing PPFD on ΔF/Fm', for a given leaf temperature, was most pronounced in S. pusilla. Despite the broad diurnal leaf temperature amplitude of alpine environments, only in S. paniculata did saturating PPFD occur over a broad range of leaf temperatures (43 K). In the other two species it was half of that (around 20 K). This indicates that the setting of environmental scenarios (leaf temperature×PPFD) in laboratory experiments often likely exceeds the actual environmental demand in the field. and V. Braun, G. Neuner.
In the bark of Populus tremula L. photochemical efficiency of photosystem 2 (PS2) determined as Fv/Fm decreased during winter. The strongest reduction was found after cold periods. The degree of reduction depended on irradiance since the lowest levels of Fv/Fm were found on the sun-exposed side of the stem and below thin phellem. Therefore, photoinhibition was partly responsible for the reduction in Fv/Fm. The photochemical efficiency of PS2 recovered in late April about a month before the trees got leaves. In the laboratory, Fv/Fm recovered within about a week under low irradiance at 20 °C. Rapid recovery of photochemical efficiency of PS2 in the bark may be important to reduce respiratory loss of CO2 from the stem before the trees get leaves. and K. A. Solhaug, J. Haugen.
The sensitivity of phytoplankton species for hydrogen peroxide (H2O2) was analyzed by pulse amplitude modulated (PAM) fluorometry. The inhibition of photosynthesis was more severe in five tested cyanobacterial species than in three green algal species and one diatom species. Hence the inhibitory effect of H2O2 is especially pronounced for cyanobacteria. A specific damage of the photosynthetic apparatus was demonstrated by changes in 77 K fluorescence emission spectra. Different handling of oxidative stress and different cell structure are responsible for the different susceptibility to H2O2 between cyanobacteria and other phytoplankton species. This principle may be potentially employed in the development of new agents to combat cyanobacterial bloom formation in water reservoirs. and M. Drábková ... [et al.].
Photosynthetic capacities of green leaves (GL) and green flower petals (GFP) of different ages of the CAM plant Dendrobium cv. Burana Jade were studied through chlorophyll (Chl) content, Chl fluorescence characteristic Fv/Fm, maximal photosynthetic O2 evolution rates (P max), and CAM acidities [dawn/dusk fluctuations in titratable acidity (TA)]. All these photosynthetic parameters were higher in GL than in GFP. Among the different ages of GFP, the young GFP had significant higher readings of all photosynthetic parameters than the oldest GFP, indicating that reduced photosynthesis occurred in the senesced GFP. The source-to-sink relationship between GL and GFP was also studied by comparing the diurnal changes in contents of total soluble and insoluble sugars and TA between the fully irradiated (FI) control (with both irradiated GL and GFP) and GL-darkened plants (covering all GL with aluminium foils, leaving only the GFP exposed to radiation). CAM acidities were much lower in GL darkened with aluminium foils compared to those of FI-GL while there were no differences in CAM acidities of their GFP. The contents of total soluble and insoluble sugars and the CAM acidities of GL towards the end of the day were lower in GL-darkened plants compared to that of FI-plants. Hence CAM acidities of GL depended on their saccharide contents. However, diurnal changes of TA in GFP were similar in all GFP regardless of their ages, with or without GL photosynthetic sources. Thus CAM acidities of GFP are independent of GL saccharides. However, lower saccharide content in GFP (especially the oldest GFP) of GL-darkened plants implies that GFP function as sinks and depend on saccharides exported from GL for its development and growth. and J. He, W. L. Woon.