The effect of inorganic (IC) depletion on fluorescence quenching was studied under laboratory conditions using the chlorococcal alga Scenedesmus quadricauda strain Greifswald/15. The absence of IC caused a decrease in photochemical quenching (^p), fluorescence yield and the photosystem 2 photochemical yield (dF/F^), and an increase of non-photochemical quenching {q^). High extemal pH (about 11), which accompanies the IC-depletion, did not háve any remarkable effect on the algae. Fluorescence parameters were reversed by a resupply of CO2. The IC-defícient algae when exposed to high irradiance appeared to be less sensitive to the photoinhibition than the algae supplied with CO2. Increased thermal dissipation of the excitation energy (non-photochemical quenching) in the absence of IC is one of the probable protective mechanisms against photoinhibitory damage.
V tomto článku se budeme zabývat analýzou nízkofrekvenčních elektromagnetických vln (tj. o frekvencích do 10 kHz) pozorovaných ve vrchní ionosféře (tj. ve výškách okolo 700 km) družicí DEMETER. Zaměříme se přitom na studium dvou rozdílných typů jevů, kterými jsou: efekty spojené se seizmickou aktivitou a čárové záření., František Němec, Ondřej Santolík, Michel Parrot., and Obsahuje bibliografii
Resonant motions of systems of mutually gravitating rigid bodies are investigated with the help of the periodic and condltionally periodic solutions for multifreguency nonlinear systems, containing a small parameter. The conditions of existence have been obtained for the periodic solutions of these systems in the principal cases as well as in some degenerate ones. The existence has been proved of the periodic solutions of three kinds In the unrestricted problem of three rigid bodies, possessing quasiconcentric distributions of densities. With the help of the periodic solutions of the first kind of this problem, a posslble explanation has been given to the observed resonance In the Venus´ motlon. Perlodlc solutions have been found In the planetary version of the problem of η + 1 rigid bodies, generalizlng the corresponding periodic solutions of the problem of η + 1 point bodies. It is supposed that the bodies of the system have small dimensions and quasiconcentric distributions of densities.
In a chlorophyll(Chl)-deficient ch5 mutant of Arabidopsis thaliana the thylakoid membrane of which is more loosely arranged than that of the wild type we characterized the xanthophyll cycle (VAZ cycle) components (violaxanthin - V, antheraxanthin - A and zeaxanthin - Z) in comparison with the wild type grown under three low irradiances. As the irradiance increased from 30 to 250 pmol m'^ s'i, the total amount of components of the VAZ cycle decreased in both biotypes, but those of the ch5 mutant decreased more slowly than did those of the wild type. In both biotypes, the relative amoímts of V and A decreased as the irradiance increased, and that of Z increased, but the increase and decrease in the ch5 mutant was slower than in the wild type. The epoxidation index showed that the VAZ cycle operated at a similar efficiency in both biotypes (between 30 and 250 pmol m‘2 s'*), but that the ch5 mutant worked at a capacity 3.5-13.5 % lower than did the wild type, depending on the irradiance. Thus in Chl-deficient mutants, the VAZ cycle operates at a lower capacity than in the wild type, and the mutants are more sensitive to the changes in irradiance.
In spring and winter cultivars of oilseed rape (Brassica napus var. oleifera), acclimation of photosynthetic apparatus to cold was connected with the increase in activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and sucrose-phosphate synthase (SPS). Conversely, cold de-acclimation entailed the decline of RuBPCO and SPS activities. The rate of this photosynthetic de-acclimation might depend on day temperature. On the other hand, temperature rise during de-acclimation (identical during the day and night) resulted in the improvement of photosynthetic activity measured by means of chlorophyll fluorescence. An increase in SPS activity (and even transitory increase in RuBPCO activity) was observed when the elongation growth rate (EGR) accelerated during de-acclimation. Throughout re-acclimation, plants with high EGR were unable to maintain or recover higher photosynthetic capacity, despite the fact that SPS activity remained high or even increased during re-acclimation. and M. Rapacz, K. Hura.