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 (Pisum sativum L.) growing at lower (4 degrees C and 10 degrees C) and higher temperatures (35 degrees C and 40 degrees C) than control plants (23 degrees C) and their acclimation ability to these conditions were investigated by means of chlorophyll (Chl) fluorescence. A temperature treatment at 10 degrees C did not significantly influence PS2 activity of pea plants: Treatment at 40 degrees C led, however, to a serious injury of the photosynthetic apparatus 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 was 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 change. An exposure of pea plants to 35 degrees C did not alter the Chi fluorescence ratios F-v/(m), or F-v/F-o but decreased the Rfd-values with increasing time of treatment. This demonstrates that at 35 degrees C the maximum photochemical quantum yield, as indicated by the ratios F-v/F-m and F-v/F-o cannot be maintained under steady state conditions of photosynthesis and thus causes a decline of Rfd-values. The changes in Chi fluorescence parameters at 4 degrees C and 35 degrees C were reversible; thus these two temperatures seem to set the temperature limits for studies on the cold and heat acclimation mechanisms of pea plants.