Photosynthetic activity during high temperature treatment of pea plants

The functional activity of the photosynthetic apparatus of pea plants (Pisu m sativum, L.) under high temperature conditions was investigated. The rate s of CO2 uptake and O-2 evolution declined after 1 h exposure to 45 degrees C and their activity did not change significantly up to the 8(th) h of tre atment, which could be due to some acclimation to the unfavourable temperat ure. Photosynthetic activity sharply decreased after 24 h at 45 degrees C. Information about the functional activity of PSII was derived from analyses of in vivo chlorophyll fluorescence. It was recorded at 25 degrees C and a lso at 45 degrees C, immediately after the respective time of 45 degrees C treatment of pea plants. Our results showed that when whole plants were exposed to 45 degrees C up t o 24h the CO2 assimilation and O-2 evolution rate were more inhibited than the yield of primary photochemistry (estimated by the ratio F-v/F-m). These values started to decrease after 5 h of high temperature exposure and was reduced to a greater extent after 24 h of treatment. The higher PSII thermostability in vivo could be due to the protective effe ct of low light intensity and the low air humidity during the heat treatmen t.