The state of some parameters of photosynthetic activity in Norway spruce (Picea abies [L.] Karst.) seedlings during the first autumn temperature transition to frost was monitored in October 1991. The trees were grown under field conditions of the Beskydy Mts. (North Moravia, The Czech Republic). Simultaneous measurements of Chi a fluorescence and C02 gas exchange revealed two phases in the functional transition of the assimilatory apparatus. Immediately upon the temperature transition to frost a distinct decrease in the radiant energy saturated rate of C02 uptake was observed and radiationless dissipation was indicated by higher values of the nonphotochemical quenching coefficient. The second period of the transition, a period with prolonged influence of frost together with a higher level of irradiance, was connected with a decrease of photosynthetic efficiency. The overwhelming capacity for protective non-photochemical energy dissipation and the complete reduction of acceptor QA occurred especially at medium and high incident irradiance documenting photoinhibitory damage to the photosynthetic apparatus.
We analyzed the effect of NaCl stress on photorespiration of spinach leaves by calculating the rate of carboxylation/oxygenation of ribulose-1,5-bisphosphate carboxylase/oxygenase, and by measuring the content of amino acids produced through photorespiration. After 20 d of NaCl stress the carboxylation rate was reduced while the oxygenation rate was not affected. The contents of serine, glycine, and alanine increased relevantly. The amount of glutamine also increased after 20 d but the amount of glutamate did not. Hence photorespiration may be stimulated under moderate NaCl stress. A relevant electron transport rate was observed under CO2-free air, which may indicate refixation of photorespiratory CO2. When NaCl accumulation proceeded for more than 20 d, photosynthesis was reduced and the content of photo-respiratory amino acids started to decrease, but the oxygenation rate did not change. and C. di Martino ... [et al.].