Morphoiinoethylesters of 2-, 3- and 4-alkoxysubstituted phenylcarbamic acids (MAPC) inhibit photosynthetic processes in algae and plant chloroplasts. The inhibitoiy activity of MAPC in photosynthesizing organisms was in good correlations with lipophilicity characteristics such as hydrophobic fragment constants, partition coefficients and chromatographic retention factors.
Metodu "kinetic impactor" (test změny trajektorie asteroidu na kolizní dráze Země) představuje Dr. Petr Pravec, pod jehož vedením česká spolupráce na tomto projektu probíhá. and Jana Žďárská, Petr Pravec.
The 77 K fluorescence emission was measured on Chlorella cells at regular intervals during adaptatíon of high CO2 (1.8 % CO2 v/v) grown cells to air level of CO2. The ratíos of the peaks at 686 and 697 nm (photosystem 2, PS 2, fluorescence) to the peak at 720 nm (PS 1 fluorescence) decreased and approached a constant level in about 1.5 h. The extemal concentration of dissolved inorganic carbon (DlC) required for the half-maximum rates of C02-dependent O2 evolutíon, 5, also decreased and reached a constant level aíter the same period of adaptatíon. Hence the íncreased demand for ATP/NADPH during the CO2 assimilatíon by the ''C02-concentrating mechanism" induces the redistribution of excitation energy from PS 2 to PS 1 and increases formation of ATP by the cyclic photophosphorylatíon.
The chlorophyll (Chl) and protein degradation during dark incubation of leaf discs was reduced by Sr2+, Ca^^, and spermine (Spm) treatments. Sr2+ inhibited most effectively the Chl degradation, which was remarkable 48 h after the treatment. The Chl degradation appeared in control discs within 24 h in the dark and Chl content decreased by about 50 % during 96 h. The proteins retained at least during 48 h of dark treatment in the presence of Sr2+, Ca2+, or Spm. The retardation effect of Sr2+, Ca2+ and Spm on the Chl loss and the disintegration of thylakoid membrane proteins may be due to a cationic protection of thylakoid membranes.
Prolonged storage of isolated photosystem 2 (PS2)-enriched subchloroplast particles in the frozen statě leads to a decrease of the PS2 activity and to an increase of the energy transfer between chlorophyll (Chl)-proteins of the light-harvesting chlorophyll a/b (LHC)-PS2 complex. The energy transfer was less influenced than the PS2-mediated electron transport at freeze-thaw treatment of PS2 particles. The change of these parameters was not affected by the rate of freezing. The addition of cryoprotectants such as glycerol, trehalose or saccharose in the suspension medium prior to freezing preserved fo a different extent the PS2-mediated electron transport and the energy transfer between the Chl molecules of the LHC-PS2 complex.
A major problém in meteor astronomy is why the orbits of meteoroids within particular streams are so dispersed. For streams with aphelia well within Jupiter (such as the Geminids) planetary perturbations cause insignificant dispersion but can accommodate the required motion of the nodal heliocentric distance to explain why the Geminids were not observed prior to the 1860's. The spread in the orbits wouid also require unreasonably large ejection velocities from the parent. Another dispersal mechanism is therefore required. By incorporating perturbations due to the Yarkovsky-Radzievskii effect into the model the Geminid
dispersal can be understood; by including also the effects of the radiation pressure and Poynting- Robertson forces the main observed characteristics of the stream (shower duration variation with magnitude; skew rate profile; changes in mass distribution and radiant diffuseness as the shower progresses) are explicable. The necessary spin rates (about 3000 rev/sec for 1 mm and 1000 rev/sec for 1 cm radius meteoroids) wouid be attained within a thousand years of release from the parent body, due to spin-up under solar radiation pressure. It therefore appears that the Yarkovsky- Radzievskii effect is an important source of stream dispersion which has been hitherto neglected, but should be included in future models.