Photosynthetic activity during high temperature treatment of pea plants

The functional activity of the photosynthetic apparatus of pea plants (Pisum sativum, L.) under high temperature conditions was investigated. The rates 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 treatment, which could be due to some acclimation to the unfavourable temperature. 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 also 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 to 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 effect of low light intensity and the low air humidity during the heat treatment.