Cotton (Gossypium hirsutum L.) yields are impacted by overall photosynthetic production. Factors that influence crop photosynthesis are the plants genetic makeup and the environmental conditions. This study investigated cultivar variation in photosynthesis in the field conditions under both ambient and higher temperature. Six diverse cotton cultivars were grown in the field at Stoneville, MS under both an ambient and a high temperature regime during the 2006-2008 growing seasons. Mid-season leaf net photosynthetic rates (PN) and dark-adapted chlorophyll fluorescence variable to maximal ratios (Fv/Fm) were determined on two leaves per plot. Temperature regimes did not have a significant effect on either PN or Fv/Fm. In 2006, however, there was a significant cultivar × temperature interaction for PN caused by PeeDee 3 having a lower PN under the high temperature regime. Other cultivars' PN were not affected by temperature. FM 800BR cultivar consistently had a higher PN across the years of the study. Despite demonstrating a higher leaf Fv/Fm, ST 5599BR exhibited a lower PN than the other cultivars. Although genetic variability was detected in photosynthesis and heat tolerance, the differences found were probably too small and inconsistent to be useful for a breeding program., W. T. Pettigrew., and Obsahuje bibliografii
In a field rain-fed trial with 15 cassava cultivars, leaf gas exchanges and carbon isotope discrimination (Δ) of the same leaves were determined to evaluate genotypic and within-canopy variations in these parameters. From 3 to 7 months after planting leaf gas exchange was measured on attached leaves from upper, middle, and lower canopy layers. All gas exchange parameters varied significantly among cultivars as well as canopy layers. Net photosynthetic rate (PN) decreased from top canopy to bottom indicating both shade and leaf age effects. The same trend, but in reverse, was found with respect to Δ, with the highest values in low canopy level and the lowest in upper canopy. There were very significant correlations, with moderate and low values, among almost all these parameters, with PN negatively associated with intercellular CO2 concentration (Ci), ratio of C i to ambient CO2 concentration C i/C a, and Δ. Across all measured leaves, Δ correlated negatively with leaf water use efficiency (WUE = photosynthesis/stomatal conductance, gs) and with gs, but positively with Ci and Ci/Ca. The later parameters negatively correlated with leaf WUE. Across cultivars, both PN and correlated positively with storage root yield. These results are in agreement with trends predicted by the carbon isotope discrimination model. and M. A. El-Sharkawy, S. M. de Tafur.
The genetic variation in low temperature sensitivity of eight tomato genotypes grown at suboptimal temperature (19 °C) and at low irradiance (140 pmol m'2 s**) was assessed at the plant, chloroplast and thylakoid membrane levels. Temperature effects on the thylakoid membrane were determined by measuring the maximum fluorescence (Fp) and the maximal fluorescence rise (ADP) of induction traces of leaf discs at decreasing temperatures (30, 28, ... 0 °C). Two discontinuities were found in Fp versus temperature curves: a low temperature break at ca. 12 °C (LTB) and a high temperature break at ca. 22 °C (FITB). Below LTB, sFp and sDP were determined as the temperature induced changes in Fp, respectively ADP. Chloroplast functioning was determined by measuring net CO2 fixation rate (E^) of leaves. Plant performance was determined by measuring the increase in leaf area and sho ot dry mass in time. Correlations between the various parameters were analysed across the genotypic variation found. Chlorophyll (Chl) fluorescence parameters were not correlated with plant performance at suboptimal growth conditions. of leaves was correlated with plant performance, but only at ambient CO2. Effects of stomatal resistance on were large. The Chl fluorescence parameters LTB, sFp and sDP could distinguish between tomato genotypes. Nevertheless, the ranking of the genotypes depended on the specific parameter selected, indicating that each parameter assessed a different aspect of the heterogeneous temperature dependence of Chl fluorescence induction. Their genetic variation suggested that the genotypes differed in the organisation and fimctioning of the thylakoid membrane. These differences were not reflected in of leaves or plant performance.
The study of leaf vascular systems is important in order to understand the fluid dynamics of water movement in leaves. Recent studies have shown how these systems can be involved in the performance of photosynthesis, which is linked to the density of the vascular network per unit of leaf area. The aim of the present study was to highlight the correlation between a leaf vein density (VD) and net photosynthetic rate (PN), which was undertaken using a digital camera, a stereoscopic microscope, and a light source. The proposed hypothesis was tested, for the first time, on the leaves of two cultivars of Vitis vinifera (L.). A significant difference was found between the VD of mature leaves of the two cultivars. VD was also significantly correlated with the maximum leaf PN. These findings support the hypothesis that the vascular system of grape leaves can be correlated with leaf photosynthesis performance., M. Pagano, P. Corona, P. Storchi., and Obsahuje bibliografii
The effect of salinity on some morpho-physiological characteristics in lisianthus cultivars was investigated. Cultivars namely, Blue Picotee (C1), Champagne (C2), Lime Green (C3), and Pure White (C4), were subjected to salt stress (0-60 mM NaCl) in a sand culture and their responses were measured. Our results showed that as a salinity level increased, growth parameters, relative water content, photosynthetic pigments, and gas-exchange characteristics decreased in all cultivars, while root fresh mass, root/shoot length ratio, electrolyte leakage, and a malondialdehyde content increased. However, the changes were less pronounced in C3 and C4 compared to C1 and C2. The regression analysis of the relationship between salinity levels and seedling height or root/shoot length ratio defined two groups with different slope coefficients: C1 and C2 as salt-sensitive cultivars and C3 and C4 as salt-tolerant cultivars. Shoot dry mass and leaf area tolerance indices were less affected by salinity in C3 and C4 compared to those in C1 and C2. Further, C3 and C4 showed higher photosynthetic rates, greater stomatal conductances, and accumulated greater K+ and Ca2+ contents and K+/Na+ ratios in roots and shoots compared to those in C1 and C2. The results suggests that C3 and C4 could be recommended as resistant cultivars due to maintaining higher growth, water balance, leaf gas exchange, ion compartmentalization, and lower lipid peroxidation in response to salinity compared to C1 and C2., N. Ashrafi, A. Rezaei Nejad., and Obsahuje bibliografii
A field experiment involving two planting densities (83,333 and 166,666 plants per ha), two cropping systems (monoculture and mixed culture) and five cowpea [Vigna unguiculata L. (Walp.)] genotypes was conducted at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to select cowpea material with superior growth and water-use efficiency (WUE). The results showed significantly higher photosynthetic rates, stomatal conductance and transpiration in leaves of plants at low density and in monoculture due to greater chlorophyll (Chl) levels relative to those at high density and in mixed culture. As a result, C concentration in leaves and the amount of C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B accumulated in shoots at low density and under monoculture were also much higher. Even though no marked differences in photosynthetic rates were found between and among the five cowpea genotypes, leaf C concentration and shoot C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B contents differed considerably, with Sanzie exhibiting the highest C concentration and C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B contents in shoots, followed by Bensogla and Omondaw, while ITH98-46 and TVu1509 had the lowest shoot concentration and contents of C, P, K, Ca, Mg, Fe, Cu, Zn, Mn, and B. WUE (calculated as photosynthate produced per unit water molecule transpired) was significantly greater in plants at low density and monoculture relative to those at high density and in mixed culture. Isotopic analysis revealed significant differences in δ13C values of sorghum [Sorghum bicolor L. (Moench.)] and cowpea, with higher δ13C values being obtained for plants at low density and in monoculture relative to those at high density or in mixed culture. The five cowpea genotypes also showed significant differences in δ13C values, with Sanzie exhibiting the most negative value (i.e. low WUE) and ITH98-46, the least negative δ13C value (i.e. high WUE). Whether measured isotopically or from gas-exchange studies, sorghum (a C4 species) exhibited much higher WUE relative to cowpea (a C3 species). Both correlation and regression analyses revealed a positive relationship between WUE from gas-exchange studies and δ13C values from isotopic analysis of cowpea and sorghum shoots. and J. H. J. R. Makoi, S. B. M. Chimphango, F. D. Dakora
Cadmium inhibits photosynthetic capacity of plants by disturbing protein conformations, whereas phytocystatins prevent degradation of target proteins and are involved in abiotic stress tolerance. Two mustard (Brassica juncea L.) cultivars, Ro Agro 4001 and Amruta, were grown with Cd (50 µM) in order to study physiological and biochemical basis of differences in Cd tolerance. Amruta accumulated higher Cd and H2O2 concentrations in leaves than that of Ro Agro 4001. Cd significantly decreased photosynthesis and growth of plants in both cultivars by reducing a chlorophyll content, gas exchange parameters, and activity of Rubisco; the effects were more prominent in Amruta than those in Ro Agro 4001. The greater photosynthesis and growth of Ro Agro 4001 under Cd stress might be attributed to its higher phytocystatin activity together with greater ascorbate peroxidase activity, photosynthetic nitrogen-use efficiency, sulphur assimilation (ATP-sulphurylase activity and S content), and contents of cysteine and reduced glutathione compared to Amruta. In contrast, the activity of superoxide dismutase (SOD) was higher in Amruta than that of Ro Agro 4001 under control conditions, whereas the Cd treatment increased significantly the SOD activity in both cultivars with the greater increase in Ro Agro 4001. The fluorescence spectra of phytocystatin showed a lesser change in Ro Agro 4001 under Cd stress than that in Amruta suggesting higher resistance of Ro Agro 4001 to Cd. The higher phytocystatin activity under Cd stress in Ro Agro 4001 compared to Amruta enabled the plants to protect their proteins more efficiently. This resulted in a greater increase of photosynthetic capacity in Ro Agro 4001 than that of Amruta. Thus, the phytocystatin activity may be considered as a physiological parameter for augmenting photosynthesis and growth of mustard under Cd stress., T. S. Per, S. Khan, M. Asgher, B. Bano, N. A. Khan., and Obsahuje bibliografii