Nitrogen defíciency caused pronounced reductions in the photosynthetic capacity and differential losses in chlorophyll, cytochrome / and Mg2'''>specific ATPase amounts or activities in suspension cultured cells of Chenopodium rubrum L. This reduced outfit of the photosynthetic machinery and limited protein tumover capacity are possible reasons for our observation that nitrogen deficiency exacerbates the hannful effects of high irradiance on photosystem 2 photochemical efficiency. The effect of nitrogen defíciency on photoinhibition increased over a broad range of photon flux densities and it was detectable in both the short-term and long-tenn experiments. Differences in the effects of the nitrogen regime and irradiance on several growth parameters were demonstrated. The main effect of nitrogen defíciency was a reduction of protein synthesis and cell division, whereas the irradiance chiefly affected the accumulation of carbon in the cell suspensions. Synergistic effects of nitrogen regime and irradiance could also be demonstrated for betalain accumulation which was the greatest under high irradiance and expressed nitrogen defíciency.
Miscanthus is one of the most promising bioenergy crops with high photosynthetic nitrogen-use efficiency (PNUE). It is unclear how nitrogen (N) influences the photosynthesis in Miscanthus. Among three Miscanthus genotypes, the net photosynthetic rate (PN) under the different light intensity and CO2 concentration was measured at three levels of N: 0, 100, and 200 kg ha-1. The concentrations of chlorophyll, soluble protein, phosphoenolpyruvate carboxylase (PEPC), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, leaf anatomy and carbon isotope discrimination (Δ) in the leaf were analyzed to probe the response of photosynthesis in Miscanthus genotypes to N levels. PN in all genotypes rose significantly as N application increased. The initial slope of response curves of PN to Ci was promoted by N application in all genotypes. Both stomatal conductance and Ci were increased with increased N supply, indicating that stomatal factors played an important role in increasing PN. At a given Ci, PN in all genotypes was enhanced by N, implying that nonstomatal factors might also play an important role in increasing PN. Miscanthus markedly regulated N investment into PEPC rather than the Rubisco large subunit under higher N conditions. Bundle sheath leakiness of CO2 was constant at about 0.35 for all N levels. Therefore, N enhanced the photosynthesis of Miscanthus mainly by increasing stomatal conductance and PEPC concentration., X.-P. Feng ... [et al.]., and Obsahuje bibliografii
In a two-year experiment (2002-2003), five N application rates [0, 60, 120, 180, and 240 kg(N) ha-1, marked N0, N60, N120, N180, and N240, respectively] were applied to sugar beet cv. Rizor arranged in a Randomized Complete Block design with six replications. Leaf shape parameters [leaf area (LA), maximum length (L), maximum width (W), average radial (AR), elongation (EL), and shape factor (SF)] were determined using an image analysis system, and leaf area index (LAI) was non-destructively measured every two weeks, from early August till mid-September (four times). Years, samplings, and their interaction had significant effects on the determined parameters. Fertilization at the highest dose (N240) increased L and sampling×fertilization interaction had significant effects on LA, L, W, and SF. For this interaction, W was the best-correlated parameter with LA and LAI meaning that W is a good predictor of these parameters. Two proposed models for LA estimation were tested. The model based on both leaf dimensions [LA = 0.5083 (L×W) + 31.928] predicted LA better than that using only W (LA = 21.686 W - 112.88). Instrumentally measured LAI was highly correlated with predicted LAI values derived from a quadratic function [LAI = -0.00001 (LA)2 + 0.0327 LA - 2.0413]. Thus, both LA and LAI can be reliably predicted non-destructively by using easily applied functions based on leaf dimensions (L, W) and LA estimations, respectively. and J. T. Tsialtas, N. Maslaris.
Five cyanobacterial symbionts from Azolla filiculoides, two symbionts from Az. microphylla and two free-living cyanobacteria Nos toe muscorum and Anabaena variabilis were analyzed for chlorophyll (Chi) a, carotenoids and phycobiliprotein contents, heterocyst frequency and nitrogenase activity. The symbiont AS-S1 as well as the free-living N. muscorum and An. variabilis contained highest amounts of Chi a and lowest amounts of carotenoids. The C-phycocyanin content was always higher than that of allo-phycocyanin and C-phycoerythrin. Among the symbionts, AS-S1 contained the highest amount of C-phycocyanin and highest nitrogenase activity. Heterocysts were more abundant in An. azollae than in free-living cyanobacteria.
Two japonica rice cultivars with different panicle trait index (PTI), HP917 (a high-PTI cultivar) and DP128 (a low-PTI cultivar) were used to investigate the effects of the nitrogen (N) rate and plant density on the grain distribution of secondary branches on the panicle axis, leaf photosynthetic characteristics, and grain yield by a split plot design. The main plots were assigned to four N rates (0, 140, 200, and 260 kg ha-1), and the subplots were assigned to two plant densities: (D20, 15 plants m-2; D10, 30 plants m-2). Results showed that the grain yield was increased by increasing N rate and plant density, reaching a peak at N200 with D10. Compared with N0 treatment, the PTIs of HP917 and DP128 increased with an increase in the N rate, respectively. The PTIs of HP917 and DP128 increased by 4% with increasing plant density from D20 to D10. The leaf capacity was significantly affected by N rate and plant density. The grain distribution characteristics of secondary branches on the panicle axis was closely related to yield. Correlation analysis showed the PTI was positively correlated with grain yield and net photosynthetic rate. These results suggested the improvement in PTI from 0.15 to 0.52 was beneficial to increase the grain yield, which might contribute to the increased grain number of secondary branches of the middle and bottom panicle.
Using intense ns-laser pulses up to 2 x 10** photons per cm^ per pulse the intensity dependence of fluorescence yield (O) of different photosystem 2 (PS2) subunits in spinách on the intensity of excitation pulse (/) was measured. A sti ong drop of O was observed with increasing laser pulse I. Measurements of the light-harvesting complex of PS2, LHC2, were taken at excitation wavelengths of 645-700 nm. A shift of the í) vs. I curves to lower I with increasing absorption cross section was observed. Measurements of PS2 and thylakoid membrane ífagments taken at a fixed excitation wavelength of 645 nm showed the same O V5, I dependences as LHC2. This suggests that LHC2-pigment proteins dominate the exciton concentration in the photosynthetic apparatus. A smáli drop of O measured at CP29 and CC2 particles was possibly caused by smaller domains. Smaller drop of O measured at D1D2 particles was similar to that of free chlorophyll (Chl), indicating that bimolecular annihilation was absent. Experimental results could be described using a simple two-level model including exciton-exciton-annihilation and depletion of Chl ground States. Good fits of measured O-intensity ciu-ves were possible for LHC2 with all the ušed excitation wavelengths. Outputs of these approximations are statements about excited statě concentration and time dependence of their decay as a function of excitation irradiance.
The review deals with thermal dissipation of absorbed excitation energy within pigment-protein complexes of thylakoid membranes in higher plants. We focus on the de-excitation regulatory processes within photosystem 2 (PS2) that can be monitored as non-photochemical quenching of chlorophyll (Chl) a fluorescence consisting of three components known as energy-dependent quenching (qE), state-transition quenching (qT), and photoinhibitory quenching (qI). We summarize the role of thylakoid lumen pH, xanthophylls, and PS2 proteins in qE mechanism. Further, both the similarity between qE and qI and specific features of qI are described. The other routes of thermal energy dissipation are also mentioned, that is dissipation within photosystem 1 and dissipation through the triplet Chl pathway. The significance of the individual de-excitation processes in protection against photo-oxidative damage to the photosynthetic apparatus under excess photon supply is stretched. and M. Štroch, V. Špunda, I. Kurasová.