The exciton equilibration in the light-harvesting complex of photosystem 2 at room temperature was studied with pump-probe experiments under quasi-stationary conditions. The measurements were performed with two dye lasers, which had a pulse diuation of 10 ns and a spectral bandwidth of less than 0.01 nm. The relative probe beam transmission ffom 640-690 nm was recorded at different excitation wavelengths, varied from 645 to 685 nm. Two maxima were observed at 650 nm (Chl b absorption region) and at 680 nm (Chl a absorption region). The relative probe beam transmission in the Chl a region showed a course nearly independent of the pump beam wavelengťh in contrast to a weak dependence in the Chl b region. Measurements of the relative probe beam transmission as a function of pump beam intensity revealed a dominating exciton-exciton annihilation in the Chl a absorption region. In the Chl b region exciton-exciton annihilation was only marginal.
We tested the usefulness of chlorophyll a fluorescence quenching analysis for the selection of maize parental inbred lines able to produce F1 hybrids with a high CO2 assimilation rate during growth at suboptimal temperature. Fifty inbred lines, grown at 15 °C, showed at 6 °C a broad genetic variability regarding the quantum yield of photosynthetic electron transport (ΦPS2). A decrease of ΦPS2 in sensitive lines was caused more by reduction of the efficiency of excitation energy capture by open photosystem 2 (PS2) reaction centres (Fv'/Fm') than by a drop in photochemical quenching (qP). Selected inbred lines with the highest (H) and the lowest (L) values of ΦPS2 were used for separate crossings in a diallelic arrangement. Twenty-one of H×H hybrids and 21 of the L×L hybrids were grown at 15 °C. The H×H hybrids showed at suboptimal temperature a significantly higher transport of photosynthetic electrons than the L×L hybrids at lower (400) as well as at higher [800 μmol(photon) m-2 s-1] irradiance. The mean net photosynthetic rate (PN) in H×H and L×L hybrids amounted to 8.4 and 5.8 (second leaf) and 8.5 and 7.6 μmol(CO2) m-2 s-1 (third leaf), respectively. Among the best 20 hybrids with regard to PN (values larger than the average) of second leaves, as many as 15 were derived from H lines (75 % of hybrids), whereas among the best 21 hybrids with regard to PN of the third leaves, 16 were derived from H lines (76 % of hybrids). The intensive PN of H×H hybrids was most often accompanied by less water lost via transpiration in relation to photosynthesis than in the hybrids of L lines. Hence an analysis of chlorophyll a fluorescence quenching enables the selection of inbred lines, which can produce hybrids with improved CO2 fixation and with efficient water management during growth at suboptimal temperature. and J. Kościelniak, F. Janowiak, Z. Kurczych.
Our aim was to investigate whether hyperthermia before exercise protects against exercise-induced skeletal muscle damage. Two hyperthermia protocols were evaluated. In the first, male ICR mice were exposed to 30 min of whole-body heat in an environmental chamber at an ambient temperature of 42 °C. Heat-exposed and non-heat-exposed mice subsequently completed 60 min of downhill running on a treadmill, 24 h after exposure. Heat exposure significantly increased HSP70 and HSP25 content in the soleus muscle compared to controls. Plasma creatine kinase, muscle β-glucuronidase, and histochemical (hematoxylin and eosin stain) analysis demonstrated that muscle damage was lower in the heatexposed mice than in the non-heat-exposed mice. In the second, the effect of regional heating of the legs, by microwave diathermy, on the prevention of exercise-induced muscle damage was evaluated in male Wistar rats. Microwave-treated and nonmicrowave-treated rats again completed the running protocol 24 h after exposure. Microwave diathermy increased the muscle temperature to 40 °C, significantly increased HSP70 and HSP25 content in the soleus muscle, and significantly attenuated exercise-induced muscle damage. Therefore, hyperthermia before exercise increases skeletal muscle HSPs and attenuates the risk of exercise-induced muscle injury.