Photosynthetic activity and acclimation ability of pea plants to low and high temperature treatment as studied by means of chlorophyll fluorescence

The functional activity of the photosynthetic apparatus of pea plants (Pisu m sativum L.) growing at lower (4 degrees C and 10 degrees C) and higher te mperatures (35 degrees C and 40 degrees C) than control plants (23 degrees C) and their acclimation ability to these conditions were investigated by m eans of chlorophyll (Chl) fluorescence. A temperature treatment at 10 degre es C did not significantly influence PS2 activity of pea plants: Treatment at 40 degrees C led, however, to a serious injury of the photosynthetic app aratus as seen in a sharp increase of the ground Chl fluorescence F-o and a decrease of the variable Chi fluorescence F-v and the ratios F-v/F-m, F-v/ F-o and the Rfd-values. At 4 degrees C a reduced photosynthetic activity wa s detectable as seen mainly in a decrease of the maximum (F-m) and variable Chi fluorescence (F-v) and in reduced Rfd-values, whereas F-o did not chan ge. An exposure of pea plants to 35 degrees C did not alter the Chi fluores cence ratios F-v/(m), or F-v/F-o but decreased the Rfd-values with increasi ng time of treatment. This demonstrates that at 35 degrees C the maximum ph otochemical quantum yield, as indicated by the ratios F-v/F-m and F-v/F-o c annot be maintained under steady state conditions of photosynthesis and thu s causes a decline of Rfd-values. The changes in Chi fluorescence parameter s at 4 degrees C and 35 degrees C were reversible; thus these two temperatu res seem to set the temperature limits for studies on the cold and heat acc limation mechanisms of pea plants.