Low temperature has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). In order to study the role of ascorbate under chilling stress, the response of an ascorbate-deficient Arabidopsis thaliana mutant vtc2-1 to low temperature (2°C) was investigated. After chilling stress, vtc2-1 mutants exhibited oxidative damage. An increase in the H2O2 generation and the production of thiobarbituric acid reactive substances (TBARS), and a decrease in chlorophyll content, the maximal photochemical efficiency of PSII (Fv/Fm) and oxidizable P700 were also noted. The ratio of ascorbate/dehydroascorbate and reduced glutathione/oxidzed glutathione in the vtc2-1 mutants were reduced, compared with the wild type (WT) plants. The activities of antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and soluble antioxidants were lower in the vtc2-1 mutants than those in WT plants. These results suggested that the ascorbate-deficient mutant vtc2-1 was more sensitive to chilling treatment than WT plants. The low temperature-induced oxidative stress was the major cause of the decrease of PSII and PSI function in the vtc2-1 mutants. Ascorbate plays a critical role of defense without which the rest of the ROS defense network is unable to react effectively., L. Y. Wang ... [et al.]., and Obsahuje bibliografii
Shade treatment was applied to tall fescue with 30% full light. The results showed that shade increased chlorophyll (Chl) content per unit leaf mass, decreased the Chl a/b ratio in the mature leaves, and decreased effective quantum yield based on Chl fluorescence compared to the full light treatment. Shade stress did not cause increased contents of malondiadehyde at the early stages of leaf development. However, normalized vegetation indices were able to detect shade stress. Chloroplasts in the shaded leaves are arranged tightly against the periclinal cell wall and are in a spindle shape. There were no differences in the number of grana per chloroplast or grana size (thylakoids per granum) between shade and full light treatment. In conclusion, tall fescue leaves showed unique ultrastructure changes. Turfgrass managers could use vegetation indices developed from the leaf light reflection spectrum as an effective tool to assess shade stress levels and make management decisions.
a1_This study evaluated the relationship between photosynthetic carbon accumulation and symbiotic nitrogen nutrition in young fully expanded leaves of 30 nodulated cowpea genotypes grown in the field at Manga, Ghana, in 2005 and 2006. Estimates of fixed-N in photosynthetic leaves revealed greater symbiotic N in genotypes with higher photosynthetic rates and increased leaf transpiration rate/efficiency. There was also greater C accumulation in genotypes with higher symbiotic N and/or total N. Additionally, genotypes with high contents of C per unit of leaf total N exhibited greater C per unit of leaf N-fixed. The C/N and C/Rubisco-N ratios were generally similar in their magnitude when compared to the C/N-fixed ratio due possibly to the fact that Rubisco accounts for a high proportion of photosynthetic leaf N, irrespective of whether the enzyme was formed from soil N or symbiotic N. Cowpea genotypes that relied heavily on soil N for their N nutrition exhibited much higher C/N-fixed ratios, while conversely those that depended more on symbiosis for meeting their N demands showed markedly lower C/N-fixed values. For example, genotypes Omondaw, Bensogla, IT93K-2045-29, and Sanzie, which respectively derived 83.9, 83.1, 82.9, and 76.3% N from fixation, recorded lower C/N-fixed ratios of 10.7, 12.2, 12.1, and 13.0 mg mg-1 in that order in 2005. In contrast, genotypes Botswana White, IT94D-437-1, TVu1509, and Apagbaala, which obtained 14.8, 15.0, 26.4, and 26.0% of their N nutrition from fixation, showed high C/N-fixed values of 84.0, 69.0, 35.2, and 40.6 mg.mg-1, respectively, in 2005., a2_This clearly indicates that genotypes that obtained less N from symbiosis and more N from soil revealed very high C/N-fixed values, an argument that was reinforced by the negative correlations obtained between the three C/N ratios (i.e. C/N, C/Rubisco-N, and C/N-fixed) and leaf N concentration, percentage nitrogen derived from fixation, total N content, amount of N-fixed, and Rubisco N. These data suggest a direct link between photosynthetic C accumulation and symbiotic N assimilation in leaves of nodulated cowpea, and where genotypes derived a large proportion of their N from fixation, photosynthetic C yield substantially increased., A. K. Belane, F. D. Dakora., and Obsahuje seznam literatury
Previous evidence has demonstrated that vertical leaves of Styrax camporum, a woody shrub from the Brazilian savanna, have a higher net photosynthetic rate (PN) compared with horizontal leaves, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. In the present study, leaf temperature (T leaf), gas exchange and chlorophyll (Chl) a fluorescence with light interception on adaxial and also on abaxial surfaces of vertical and horizontal mature fully-expanded leaves subjected to water deficit (WD) were measured. Similar
gas-exchange and fluorescence values were found when the leaves were measured with light interception on the respective surfaces of horizontal and vertical leaves. WD reduced N values measured with light interception on leaf surfaces of both leaf types, but the effective quantum yield of PSII (ΦPSII) and the apparent electron transport rate (ETR) were reduced only when the leaves were measured with light interception on the adaxial surface. WD did not decrease the maximum quantum yield of PSII (Fv/Fm) or increase T leaf, even at the peak of WD stress. Vertical leaf orientation in S. camporum is not related to leaf heat avoidance. In addition, the similar P N values and the lack of higher values of ΦPSII and ETR in vertical compared with horizontal leaves measured with light interception by each of the leaf surfaces suggests that the vertical leaf position is not related to photoprotection in this species, even when subjected to drought conditions. The exclusion of this photoprotective role could raise the alternative hypothesis that diverse leaf angles sustain whole plant light interception efficiency increased in this species., A. M. Feistler, G. Habermann., and Obsahuje bibliografii
The aim of this study was to investigate the effects of silicon in alleviating cadmium stress in maize plants grown in a nutrient solution and to evaluate the potential of the spectral emission parameters and the ratio of red fluorescence (Fr) to far-red fluorescence (Ffr) in assessing the beneficial effects of Si. An experiment was carried out using a nutrient solution with a toxic dose of Cd and six doses of Si; biomass, Cd, Si, and photosynthetic pigments of the plants were measured. Chlorophyll (Chl) a fluorescence analysis demonstrated that Si alleviated Cd toxicity in plants. Chl fluorescence measurements were sensitive in detecting such effects even when significant changes in biomass production and concentrations of photosynthetic pigments were not observed. The spectral emission and the Fr/Ffr ratio were sensitive to the effects of Si. Silicon caused a reduction in the translocation of Cd to the shoots of maize plants., A. J. Silva, C. W. A. Nascimento, A. S. Gouveia-Neto., and Obsahuje seznam literatury
Based on the examination and quantitative comparison of the approaches used to assess the energy partitioning in photosystem II, the unified method was proposed to calculate the contribution of the components of nonphotochemical quenching. and D. Kornyeyev, C. R. Guadagno, N. D’Ambrosio.
Twenty-five genotypes of early CIMMYT hexaploid wheat were screened for salt tolerance in a glasshouse experiment using photosynthetic capacity and water relation parameters as selection criteria. Under salt stress (150 mM NaCl) the genotypes Frontana, Norin-10, Mayo-54, Noreste-66, and Yaktana-54 excelled all other lines in shoot dry mass, and Na(20)TPP, Penjamo-62, Inia-66, Frontana, Siete Cerros, and Jaral-66 in grain yield per plant in both absolute and relative (percent of control) terms. Although net photosynthetic rate (PN) declined in all genotypes due to salt stress, it was not helpful in discriminating among genotypes according to salt tolerance. Similarly, no positive relationships of salt tolerance of the genotypes with stomatal conductance, leaf water potential, or turgor pressure were found. Every genotype used its own specific mechanism to tolerate salt stress. However, a large amount of variation in salt tolerance observed in 25 early CIMMYT wheat genotypes can be of considerable practical value for improving salt tolerance in the existing commercial hexaploid wheats. and M. Ashraf, M. Shahbaz.
Photosynthetic parameters including net photosynthetic rate (P N), transpiration rate (E), water-use efficiency (WUE), and stomatal conductance (g s) were studied in indoor C3 plants Philodendron domesticum (Pd), Dracaena fragans (Df), Peperomia obtussifolia (Po), Chlorophytum comosum (Cc), and in a CAM plant, Sansevieria trifasciata (St), exposed to various low temperatures (0, 5, 10, 15, 20, and 25°C). All studied plants survived up to 0°C, but only St and Cc endured, while other plants wilted, when the temperature increased back to room temperature (25°C). The P N declined rapidly with the decrease of temperature in all studied plants. St showed the maximum P N of 11.9 μmol m-2 s-1 at 25°C followed by Cc, Po, Pd, and Df. E also followed a trend almost similar to that of P N. St showed minimum E (0.1 mmol m-2 s-1) as compared to other studied C3 plants at 25°C. The E decreased up to ≈4-fold at 5 and 0°C. Furthermore, a considerable decline in WUE was observed under cold stress in all C3 plants, while St showed maximum WUE. Similarly, the g s also declined gradually with the decrease in the temperature in all plants. Among C3 plants, Pd and Po showed the maximum g s of 0.07 mol m-2 s-1 at 25°C followed by Df and Cc. However, St showed the minimum gs that further decreased up to -4-fold at 0°C. In addition, the content of photosynthetic pigments [chlorophyll a, b, (a+b), and carotenoids] was varying in all studied plants at 0°C. Our findings clearly indicated the best photosynthetic potential of St compared to other studied plants. This species might be recommended for improving air quality in high-altitude closed environments., S. M. Gupta, A. Agarwal, B. Dev, K. Kumar, O. Prakash, M. C. Arya, M. Nasim., and Obsahuje seznam literatury
Cuttings of five Populus alba clones (S18 F1-26, Al29 F8-35, J3 F1-4, GU1 F16-36, PO9 F21-88), Populus euphratica, and Populus×euramericana (I-214) were submitted during 45 d to regular watering with NaCl solutions of electrical conductivity of 7 and 14 dS m-1. Chlorophyll a fluorescence in response to the salinity stress was assessed, using F0 and Fv/Fm. Differences in reaction to the salt were found in P. alba clones, F0 and Fv/Fm being the fluorescence parameters used to check out this stress. Minimal constant fluorescence of dark-adapted plants (F0) showed a better correlation with the disease index exhibited by plants and also with salinity dose than the parameter Fv/Fm. Some of the P. alba clones showed the same behaviour, assessed through fluorescence parameters, as P. euphratica, which was previously defined as salt tolerant, while the rest exhibited the same characteristics as I-214, which was very sensitive. and H. Sixto, I. Aranda, J. M. Grau.
Waterlogging is one of the critical factors controlling the distribution, regeneration, and survival of vegetation in wetlands. Here, we tested the hypothesis that Mitragyna parvifolia (Roxb.) Korth. and Syzygium cumini Keels, inhabiting the Keoladeo National Park, a Ramsar wetland (Bharatpur, India), are tolerant to waterlogging. The morphological and photosynthetic variables of four-month-old seedlings subjected to waterlogging, along with the concentrations of macroand micronutrients, were examined. After 35 days, treatment was halted due to high mortality of S. cumini seedlings in contrast to that of M. parvifolia seedlings. Significant declines in most of the studied variables were observed in both species when compared with their respective controls. In addition, M. parvifolia seedlings developed adventitious roots and lenticels and showed an increased root biomass. Based on the results, we concluded that adaptive traits displayed by M. parvifolia seedlings facilitate its tolerance to waterlogging in contrast to S. cumini seedlings., A. Bidalia, Z. Okram, M. Hanief, K. S. Rao., and Obsahuje bibliografii