In this study, we presented the most commonly employed net photosynthetic light-response curves (PN/I curves) fitted by the Solver function of Microsoft Excel. Excel is attractive not only due to its wide availability as a part of the Microsoft Office suite but also due to the increased level of familiarity of undergraduate students with this tool as opposed to other statistical packages. In this study, we explored the use of Excel as a didactic tool which was built upon a previously published paper presenting an Excel Solver tool for calculation of a net photosynthetic/chloroplastic CO2-response curve. Using the Excel spreadsheets accompanying this paper, researchers and students can quickly and easily choose the best fitted PN/I curve, selecting it by the minimal value of the sum of the squares of the errors. We also criticized the misuse of the asymptotic estimate of the maximum gross photosynthetic rate, the light saturation point estimated at a specific percentile of maximum net photosynthetic rate, and the quantum yield at zero photosynthetic photon flux density and we proposed the replacement of these variables by others more directly linked to plant ecophysiology. and F. de A. Lobo ... [et al.].
In the pursuit of knowledge on the biological behavior of Brazilian Atlantic Forest tree species, this study evaluated the susceptibility of the light-demanding species, Schinus terebinthifolia Raddi., Pseudobombax grandiflorum (Cav.) A. Robyns and Joannesia princeps Vell., and of the shade-tolerant species, Hymenaea courbaril L. var. stilbocarpa and Lecythis pisonis Camb, to photoinhibition and acclimation capacity. These species were first cultivated under two irradiance conditions, I20 (20% direct sunlight radiation) and I100 (all-sky or direct sunlight) and then transferred from I20 to I100. The effects of the sudden increase in light radiation intensity on photosynthetic activity were then evaluated through chlorophyll (Chl) fluorescence imaging, HPLC xanthophylls analysis, and cell membrane lipid peroxidation measurements. Light-demanding species were found to present a higher photochemical efficiency and higher acclimation capacity under high light irradiance than shade-tolerant species. The higher photoinhibition tolerance observed in light-demanding species was associated to their higher capacity for photochemical dissipation and dissipation of excess excitation energy via the xanthophyll cycle, leading to a lower ROS generation. The obtained results suggested that a knowledge of acclimation capacity, by means of Chl fluorescence imaging yields, is a useful indicator of species successional grouping., L. Dos Anjos, M. A. Oliva, and K. N. Kuki., and Obsahuje bibliografii
The kinetics of bacteriochlorophyll fluorescence in intact cells of the purple nonsulfur bacterium Rhodobacter sphaeroides were measured under continuous and pulsed actinic laser diode (808 nm wavelength and maximum 2 W light power) illumination on the micro- and millisecond timescale. The fluorescence induction curve was interpreted in terms of a combination of photochemical and triplet fluorescence quenchers and was demonstrated to be a reflection of redox changes and electron carrier dynamics. By adjustment of the conditions of single and multiple turnovers of the reaction center, we obtained 11 ms-1 and 120 μs-1 for the rate constants of cytochrome c23+ detachment and cyclic electron flow, respectively. The effects of cytochrome c2 deletion and chemical treatments of the bacteria and the advantages of the fluorescence induction study on the operation of the electron transport chain in vivo were discussed., G. Sipka, M. Kis, J. L. Smart, P. Maróti., and Obsahuje bibliografické odkazy
Photosynthetic organs are often characterized by anthocyanins being accumulated either in the epidermal or in the mesophyll cells making these tissues to turn reddish-brown in colour. It has been hypothesized that these pigments protect underlying chloroplasts from light-stress because they absorb photons of the photosynthetically active waveband. However, the photoprotective role of anthocyanins has not been undoubtedly shown on a broad range of species. In this study, green and anthocyanic areas of leaves of Pelargonium × hortorum, the latter possessing variable levels of anthocyanins, were compared using pigment analysis and pulse amplitude modulated in vivo chlorophyll (Chl) fluorescence. Quenching analysis of the induction and dark relaxation curves of slow Chl fluorescence kinetics showed that at photoinhibitory conditions [by applying above-saturation light intensity of 1,600 μmol(quantum) m-2 s-1 white light at low (4°C) temperature], anthocyanic areas were at least equally sensitive to photoinhibition as green leaf areas. In fact, the level of photoinhibition tended to be proportional to the level of anthocyanin accumulation suggesting that this characteristic was indicative of the photoinhibitory risk. The results of the present study clearly show that anthocyanins in leaf areas of Pelargonium do not afford a photoprotective advantage., G. Liakopoulos, I. Spanorigas., and Obsahuje bibliografii
Brassinosteroids (BRs), an important class of plant steroidal hormones, play a significant role in the amelioration of various biotic and abiotic stresses. 24-epibrassinolide (EBR), an active brassinosteroid, was applied exogenously in different concentrations to characterize a role of BRs in tolerance of melon (Cucumis melo L.) to high temperature (HT) stress and to investigate photosynthetic performance of HT-stressed, Honglvzaocui (HT-tolerant) and Baiyuxiang (HTsensitive), melon variety. Under HT, Honglvzaocui showed higher biomass accumulation and a lower index of heat injury compared with the Baiyuxiang. The exogenous application of 1.0 mg L-1 EBR, the most effective concentration, alleviated dramatically the growth suppression caused by HT in both ecotypes. Similarly, EBR pretreatment of HTstressed plants attenuated the decrease in relative chlorophyll content, net photosynthetic rate, stomatal conductance, stomatal limitation, and water-use efficiency (WUE), as well as the maximal quantum yield of PSII photochemistry (Fv/Fm), the efficiency of excitation capture of open PSII center, the effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching coefficient, and the photon activity distribution coefficients of PSI (α). EBR pretreatment further inhibited the increase in intracellular CO2 concentration, leaf transpiration rate, minimal fluorescence of dark-adapted state, nonphotochemical quenching, thermal dissipation, and photon activity distribution coefficients of PSII. Results obtained here demonstrated that EBR could alleviate the detrimental effects of HT on the plant growth by improving photosynthesis in leaves, mainly reflected as up-regulation of photosynthetic pigment contents and photochemical activity associated with PSI. and Y. P. Zhang ... [et al.].
In the past decade, utilization of nanostructured materials has increased intensively in a wide range of applications. Titanium dioxide nanoparticles (TiO2 NPs), for instance, can be applied for the inactivation of various pathogens through photo-induced generation of reactive oxygen species. Although TiO2 NPs with high antimicrobial activity are of great importance, in practice, their phytotoxic effects have not yet been fully clarified. In this study, we investigated the potential phytotoxicity of TiO2 NPs on grapevine (Vitis vinifera L.) under field conditions. After foliar exposure, two particularly stress-sensitive parameters, photosynthetic function and the flavonol profile, were examined. Micro- and macroelement composition of the leaves was also studied by ICP-AES measurements. We found that TiO2 NPs significantly decreased the net CO2 assimilation and increased stomatal conductance, indicating metabolic (nonstomatal) inhibition of the photosynthesis. The lower electron transport rate and lower nonphotochemical quenching in treated leaves are indicative of diminished photoprotective processes., P. Teszlák, M. Kocsis, A. Scarpellini, G. Jakab, L. Kőrösi., and Obsahuje bibliografii
Despite the elimination of the original forest and frequent cultivation using slash and burn, a large spread in leaf δ13C was recorded in weeds, crops, and bush fallow species, reflecting a forest environment rather than a broken canopy or open environment., A. De Rouw, J .F. Maxwell, C. Girardin., and Obsahuje bibliografii
IsiA is a membrane-bound Chl a-antenna protein synthesized in cyanobacteria under iron deficiency. Since iron deficiency is a common nutrient stress in significant fractions of cyanobacterial habitats, IsiA is likely to be essential for some cyanobacteria. However, the role it plays in cyanobacteria is not fully understood. In this review paper, we summarize the research efforts directed towards characterizing IsiA over the past three decades and attempt to bring all the pieces of the puzzle together to get a more comprehensive understanding of the function of this protein. Moreover, we analyzed the genomes of over 390 cyanobacterial strains available in the JGI/IMG database to assess the distribution of IsiA across the cyanobacterial kingdom. Our study revealed that only 125 such strains have an IsiA homolog, suggesting that the presence of this protein is a niche specific requirement, and cyanobacterial strains that lack IsiA might have developed other mechanisms to survive iron deficiency., H.-Y. S. Chen, A. Bandyopadhyay, H. B. Pakrasi., and Obsahuje bibliografické odkazy
To investigate the relationship between early nutritional experience, ontogeny of the small intestinal functions and predisposition to obesity development, the following experimental models of male Sprague-Dawley rats were used: 1) rats in which the quantity of nutrition was manipulated from birth to weaning (day 30) by adjusting the number of pups in the nest to 4 (SL), 10 (NL) and 16 pups (LL) and 2) littermates of SL, NL and LL rats fed either a standard or a hypercaloric diet from days 80 to 135 of age. The overfed SL pups were overweight after day 15 and became permanently obese, whereas the underfed smaller LL pups, due to accelerated growth and enhanced food intake from day 30 to day 35, attained a body fat level that did not differ from normally fed NL rats. Moreover, a significantly increased duodenal and jejunal alkaline phosphatase (AP) activity was found in SL and LL rats and these acquired somatic and intestinal characteristics persisted from weaning throughout life. Eight weeks of high-energy diet feeding elicited a similar pattern of intestinal response in SL and LL rats that was clearly different from NL rats. Despite energy overconsumption in these three groups, both SL and LL rats still displayed enhanced AP activity and showed a significant increase in protein/DNA ratio accompanied with a significant body fat accretion. These results indicate that the postnatally acquired small intestinal changes induced by over- and undernutrition could be involved in the similar predisposition to obesity risk in later life when caloric density of the diet is raised., Š. Možeš, Z. Šefčíková, Ľ. Lenhardt., and Obsahuje bibliografii a bibliografické odkazy