Temperature dependence (25-50 °C) of chlorophyll (Chl) fluorescence induction, far-red radiation (FR)-induced relaxation of the post-irradiation transient increase in apparent F0, and the trans-thylakoid proton gradients (ΔpH) was examined in maize leaves. Temperatures above 30 °C caused an elevation of F0 level and an enhancement of F0 quenching during actinic irradiation. Millisecond delayed light emission (ms-DLE), which reflects the magnitude of ΔpH, decreased strikingly above 35 °C, and almost disappeared at 50 °C. It indicates that the heat-enhanced quenching of F0 under actinic irradiation could not be attributed mainly to the mechanism of ΔpH-dependent quenching. The relaxation of the post-irradiation transient increase in apparent F0 upon FR irradiation could be decomposed into two exponential components (τ1 = 0.7-1.8 s, τ2 = 2.0-9.9 s). Decay times of both components increased with temperature increasing from 25 to 40-45 °C. The bi-phasic kinetics of FR-induced relaxation of the post-irradiation transient increase in apparent F0 and its temperature dependence may be related to plastoquinone (PQ) compartmentation in the thylakoid membranes and its re-organisation at elevated temperature. and Ming-Xian Jin, De-Yao Li, Hualing Mi.
The effect of four different NaCl concentrations (from 0 to 102 mM NaCl) on seedlings leaves of two corn (Zea mays L.) varieties (Aristo and Arper) was investigated through chlorophyll (Chl) a fluorescence parameters, photosynthesis, stomatal conductance, photosynthetic pigments concentration, tissue hydration and ionic accumulation. Salinity treatments showed a decrease in maximal efficiency of PSII photochemistry (Fv/Fm) in dark-adapted leaves. Moreover, the actual PSII efficiency (ϕPSII), photochemical quenching coefficient (qp), proportion of PSII centers effectively reoxidized, and the fraction of light used in PSII photochemistry (%P) were also dropped with increasing salinity in light-adapted leaves. Reductions in these parameters were greater in Aristo than in Arper. The tissue hydration decreased in salt-treated leaves as did the photosynthesis, stomatal conductance (g s) and photosynthetic pigments concentration essentially at 68 and 102 mM NaCl. In both varieties the reduction of photosynthesis was mainly due to stomatal closure and partially to PSII photoinhibition. The differences between the two varieties indicate that Aristo was more susceptible to salt-stress damage than Arper which revealed a moderate regulation of the leaf ionic accumulation. and H. Hichem, A. El Naceur, D. Mounir.
This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 μmol(CO2) mol-1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m-2 s-1 (control light) or 1,900 μmol m-2 s-1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (PN) and a rise in the ratio of intercellular to ambient CO2 concentration (Ci/Ca) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (ΦPSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in PN, Ci/Ca, ΦPSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE. and C. Arena, L. Vitale, A. Virzo de Santo.
Leaf area is one of the most important parameter for plant growth. Reliable equations were offered to predict leaf area for Zea mays L. cultivars. All equations produced for leaf area were derived as affected by leaf length and leaf width. As a result of ANOVA and multiregression analysis, it was found that there was a close relationship between actual and predicted growth parameters. The produced leaf-area prediction model in the present study is LA =
a + b L + c W + d LZ where LA is leaf area, L is leaf length, W is maximum leaf width, LZ is leaf zone and a, b, c, d are coefficients.
R2 values were between 0.88-0.97 and standard errors were found to be significant at the p<0.001 significance level. and F. Oner ... [et al.].
The rainy season affects the development of maize in Liaoning Province in China. Continuous, rainy weather and scant sunlight result in poor pollination, bald tips, and in an abnormally high, barren stalk. Field studies were conducted at the kernel formation stage (3-11 d after silking). Paired, near-isogenic lines of nonbarren stalk (Shennong 98B) and barren stalk (Shennong 98A) were exposed to 38, 60, and 75% shading to investigate changes in photosynthesis and chlorophyll (Chl) fluorescence characteristics under different light intensities. Net photosynthetic rate (PN), leaf maximum photochemical efficiency of PSII (Fv/Fm), photochemical quenching of Chl fluorescence (qP), and actual photochemical efficiency of PSII (ΦPSII) of Shennong 98B were always higher than those of Shennong 98A under natural light, contrary to nonphotochemical quenching (NPQ). Fv/Fm, ΦPSII, and qP increased, while PN and electron transport rate (ETR) decreased after shading, and this was aggravated with increasing shade intensity. PN, qP, ΦPSII, and ETR were lower than the values in natural light condition after seven days of shading. NPQ, Fv/Fm, ΦPSII, qP, and ETR recovered, when shading was removed. The PN of two inbred lines returned soon to the control levels after 38% shade. Under shade and natural light conditions, the PN and Chl fluorescence characteristics of Shennong 98A were both lower than those of Shennong 98B. We suggest that a poor adaptability to low light is an important physiological reason for inducing barren stalk in low light-sensitive maize., X. M. Zhong, Z.S. Shi, F.H. Li, H.J. Huang., and Obsahuje bibliografii