Results 1 - 10 of 1967
Results 1 - 10 of 1967. Search took: 0.022 seconds
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[en] This contribution presents low-temperature absorption, both broad-band and site-selective excited fluorescence, and persistent hole burning spectra of Photosystem II complexes from the Photosystem I-lacking strains of the cyanobacterium Synechocystis sp. PCC 6803 differing in the content of small putative chlorophyll-binding proteins (Scps). These proteins are homologous to light-harvesting complex of higher plants and may bind pigments. The excited state lifetimes of the complexes were determined from zero-phonon hole widths extrapolated to zero-burning dose. The area and spectral position of a phonon side-band with respect to the zero-phonon hole provided additional information concerning chlorophyll-protein coupling and the Stokes shift. Decrease of three absorption subbands at (670.0, 672.9, and 675.7 nm) in the Photosystem II isolated from the strain lacking ScpC and ScpD is in agreement with a hypothesis about the role of Scps in the chlorophyll binding. In addition, narrowing of the zero-phonon hole in Photosystem II without both Scps indicates slowering of the excitation energy transfer which may be explained by the absence of a protective excitation energy quenching related to the presence of Scps
[en] Full text: We present a theory of optical spectra of pigment-protein complexes that allows to include both the excitonic and the exciton-vibrational coupling on an equal footing. The theory is applied to two different types of the water soluble chlorophyll binding protein (WSCP) containing chlorophyll dimers. First, it is tested in simulation of optical spectra of class IIb WSCP with known crystal structure, and then it is applied to class IIa WSCP with unknown structure, in order to check whether a similar arrangement of chlorophylls as in type IIb WSCP can be assumed. Using a homology modeling of the unknown structure in combination with quantum chemical/ electrostatic calculations we propose an explanation of the 10 nm redshift observed of its optical bands with respect to class IIb WSCP. (author)
[en] Seven newly developed rice cultivars i.e., KS-133, DR-83, DR-64, BR-601, Gomal, JP-5 and Gomal-6, were evaluated for salinity tolerance in a glass house along with three varieties of known salinity tolerance i.e., KS-282 (tolerant), IR-6 (medium tolerant) and Basmati-385 (susceptible). Based on the survival percentage at 50 mol/m3 sodium chloride salinity imposed at seedling stage, rice cultivars KS-133, Gomal, and DR-83 showed high survival comparable to that of salinity tolerant cultivars like KS-282, and were thus placed in tolerance range. Survival percentage of JP-5, Gomal-6 and DR-64 remained in medium tolerance range (35 to 38%) as that of IR-6. The rice cultivar BR-601 showed only 13% survival and was found to be as sensitive towards salinity as Basmati-385. The results of rice survival in saline medium showed good uniformity and the check varieties showed results corresponding to those found elsewhere. Sodium (Na/sup +/) and potassium (K/sup +/) concentrations in the third leaf showed variations among different rice cultivars under salinity. There was an inverse correlation between varietal leaf Na/sup +/ vs survival percentage (r = -0.808) and Na/sup +/ vs leaf chlorophyll (r -0.857). The correlation between K/sup +/ and final survival percentage was direct (r = 0.744) and also leaf chlorophyll vs survival (r = 0.952). The shoot fresh and dry weights were greater in the rice genotypes having higher final survival percentage under saline conditions. Therefore, in addition to final survival percentage, the higher shoot fresh and dry weight under salinity could be also used as criterion for evaluation of salinity tolerance of rice. (author)
[en] An analytical three-band algorithm for spectrally estimating chlorophyll-a (Chl-a) has been proposed recently and the model does not need to be trained. However, the model did not consider the effects of the absorption due to colored detritus matter (CDM) and backscattering of the water column, resulting in an overestimation when Chl-a < 50 mg m-3 and an underestimation when Chl-a ≥ 50 mg m-3. In this letter, an improved three-band algorithm is proposed by integrating both backscattering and CDM absorption coefficients into the model. The results demonstrate that the improved three-band model resulted in more accurate estimation of Chl-a than the previously used three-band model when they were applied to water samples collected from five highly turbid water bodies with Chl-a ranging from 2.54 to 285.8 mg m-3. The best results, after model modification, were observed in three Indiana reservoirs with R2 = 0.905 and relative root mean square error of 20.7%, respectively.
[en] The optimum gamma irradiation treatments for the inhibition of greening of unwashed Up-to-Date potatoes exposed to continuous fluorescent lighting were 0,15 and 0,20 kGy. The 0,15 and 0,20 kGy treated potatoes took 8,7 and 10,3 d longer respectively than the controls for 50% of the potatoes to turn green. The results were verified by chlorophyll determinations. The solanine content of the γ-irradiated potatoes did not differ significantly from that of the controls during the period of exposure. Gamma irradiated tubers which were removed from continuous fluorescent lighting after 7 d to 'household' conditions of daylight and fluorescent light alternated with darkness maintained the quality of day 7 for at least another 16 d. Factors such as washing, packaging, display temperature, post-irradiation pre-illumination storage and cultivar differences did not detract from the effectiveness of γ-irradiation in retarding the greening of potatoes. A comparison of γ-irradiation with dipping inedible oil showed the latter treatment to be more effective than irradiation in inhibiting greening but the treatment caused serious rotting. No difference in the taste or colour of irradiated and nonirradiated potatoes cooked in various ways could be detected
[af]Die optimale gamma-bestralingsbehandelings vir die vergroeningsvertraging van ongewaste Up-to-Date-aartappels wat onafgebroke aan buislig blootgestel is, was 0,15 en 0,20 kGy. Die aartappels wat met dosisse van 0,15 en 0,20 kGy behandel is, het onderskeidelik 8,7 en 10,3 d langer as die kontroles geneem vir 50% van die aartappels om te vergroen. Hierdie resultate is met chlorofil-analises bevestig. Die solanieninhoud van die γ-bestraalde aartappels het gedurende die blootstellingstydperk nie betekenisvol van die kontroles verskil nie. Gammabestraalde knolle wat na blootstelling van 7 d aan onafgebroke buislig na 'huishoudelike' toestande van dag- en buislig afgewissel met donker oorgeplaas is, het die gehalte van dag 7 vir ten minste 'n verdere 16 d gehandhaaf. Faktore soos was, verpakking, uitstaltemperatuur, opberging na bestraling en voorafbeligting en cultivarverskille het nie afbreuk aan die doeltreffendheid van γ-bestraling gedoen om vergroening te vertraag nie. 'n Vergelyking van γ-bestraling met indompeling in eetbare olie het getoon dat laasgenoemde behandeling vergroening doeltreffender as γ-bestraling vertraag, maar die behandeling veroorsaak ernstige verrotting. Geen verskille kon in die smaak en kleur van bestraalde aartappels wat op verskeie maniere gaargemaak is, bespeur word nie
[en] Aim of study: We evaluated the use of dimethylsulfoxide (DMSO) for the photometric determination of chlorophyll (Chla and Chlb) and carotenoids in Quercus ilex L. leaves by comparative analysis using aqueous-acetone extraction. Area of study: a Q. ilex dehesa in Las Majadas del Tietar, Cáceres, Spain Material and methods: Q. ilex leaves were sampled during two vegetative periods. Field SPAD-502 Chlorophyll measurements and photometric chlorophyll determinations were performed. Two procedures were used: extraction of intact foliar discs at 65ºC with DMSO and fine foliar powder with cold aqueous-acetone. Main results: DMSO produced Chlb overestimation and different fitting performance for SPAD vs pigment calibrations (R2=0.64, RMSE=0.20, p<0.0001 for Chla (µg/cm2); R2=0.33, RMSE=0.23, p<0.0001 for Chlb (µg/cm2) and R2=0.50, RMSE=0.23, p<0.0001 for carotenoids (µg/cm2)). Aqueous-acetone provided more accurate predictions (R2=0.90, RMSE=0.16, p<0.0001 for Chla and R2=0.91, RMSE=0.16, p<0.0001 for Chlb, R2=0.90, RMSE=0.02, p<0.0001 for carotenoids) and mean ratio Chla/Chlb=3.6 inside the range for sun exposed leaves. Research highlights: Oxidizing conditions and polyphenol concentrations in Q. ilex leaves generated brown coloration in the DMSO extraction procedure, interfering with the photometric measurements in the red-orange region. Aqueous-acetone extraction was free from interference. DMSO should be avoided for pigment determination in Q. ilex leaves or when comparing different tree species.
[en] The effect of five doses of gamma radiation: 10, 100, 500, 1000 and 5000 Gy on chlorophylls content, net photosynthesis and respiration of Chlorella pyrenoidosa has been studied. A decrease in chlorophylls levels is produced after irradiation at 500, 1000 and 5000 Gy, being, at first b chlorophyll affected to a greater extent than a chlorophyll. Net photosynthesis and respiration decline throughout the time of the observation after irradiation, this depressing effect being much more remarkable for the first one. Met photosynthesis inhibition levels of about 30% are got only five hours post irradiation at a dose of 5000 Gy. Radio estimation by low doses, although obtained in some cases for tho 10 Gy dose, has not been statistically confirmed. (Author) 23 refs