The bicarbonate compensation concentration (BCC) measmed in Scenedesmus quadricauda increased significantly with increasing total alkalínity (TA): ířom 2-5 inmol(HC03') m'^ at an alkalinity of 0.5 mol m'^ to 416-444 mmol(HC03") m"^ at an alkalinity of 10 mol m'^. This should be taken into account when evaluating a species ability to use HC03’. The increase of BCC at higher alkalinities could be caused by carbonate inhibition of HC03‘ uptake and/or by extremely high assimilatory pH reached.
Translational efficiency of wheat ribosomes was studied as a function of an in vivo temperature pretreatment of wheat seedlings. The ribosomes were isolated from 41 oř 36 oC-adapted and non-adapted (20 oQ wheat seedlings. The poly-U-dependent translational efficiency, measured as ^H phenylalanine incorporation into poly-Phe, was enhanced up to 3-fold in the heat-adapted ribosomes. The adaptive enhancement was due to the large ribosomal subunit, as demonstrated earlier by heterologous recombination of ribosomal subímits, obtained from the plants pretreated by different temperatures. According to this, the pattem of ribosomal proteins of the large subunit exhibited pronounced differences as a function of preadaptation temperature: one spot increased markedly in the protein staining intensity on the two-dimensional polyacrylamide gels, while another almost disappeared. Two minor protein spots disappeared at high preadaptation temperatures. An evaluation of the protein phosphorylation of ribosomal proteins yielded a decreased ^zp-iabel degree in čase of the smáli subunit of heat-adapted ribosomes. These results are considered to be an important molecular correlation to phenotypical temperature adaptatíon of in vivo protein synthesis in wheat, where the optimum temperature of ^‘♦C-leucine incorporation into the total protein fraction, as a measure of in vivo protein synthesis, shifts to higher grades with increasing preadaptation temperature of the wheat seedlings. Besides Triticum aestivum L. (spring wheat; cv. Kolibri), heat adaptatíon potentíals of T. dicoccoides (tetraploid), T. longissimum (2n), T. monococcum (2n), T speltoides (2«) and T. tauschii (2n) were investígated. The temperature coefficient p (apparent actívation energy) also underwent adaptive alteratíons, although these changes were not unidirectíonal. T. tauschii proved to be the species with the most pronounced adaptive potentíal in the high temperature range, surpassed only by the heat adaptability of 14 d-postanthesis caryopses: its optimum temperature of in vivo protein synthesis rose by more than 20 «€ after a 38 oC-preadaptation period (2 d).
High-irradiance (HI) induced changes in heat emission, fluorescence, and photosynthetic energy storage (EST) of shade grown sugar maple (Acer saccharum Marsh.) saplings were followed using modulated photoacoustic and fluorescence spectroscopic techniques. HI-treatment at 900-4400 µmol m-2 s-1 for 15 min caused an increase in heat emission and a decrease in EST. In some leaves, HI-treatment of 900 µmol m-2 s-1 for 1 min induced a rapid increase in heat emission with a marginal decrease in EST. Parallel to the increase in heat emission, there was a decrease in fluorescence, and this phenomenon was reversible in darkness. Quenching of thermal energy dissipation and a recovery in EST were observed during the first 15 min after the HI-treatment. This down-regulation of photochemical activity and its recovery may be one of the photoprotective mechanisms in shade grown sugar maple plants. The increase in thermal energy dissipation was greater in the red absorbing long wavelength (640-700 nm) region than in the blue absorbing short wavelength region of photosynthetically active excitation radiation. The photochemical activity was affected more in short wavelengths (400-520 nm) than in the long wavelength region of the spectrum. This can be due to the migration of light-harvesting chlorophyll (Chl) a/b protein complex from photosystem (PS) 2 to PS1 and/or to the disconnection of carotenoid pool from Chls in the pigment bed of photosynthetic apparatus. and K. Veeranjaneyulu, R. M. Leblanc.