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 O2 evolution declined after 1 h exposure to 45 °C and their activity did not change significantly up to the 8th h of treatment, which could be due to some acclimation to the unfavourable temperature. Photosynthetic activity sharply decreased after 24 hat 45 °C. Information about the functional activity of PSII was derived from analyses of in vivo chlorophyll fluorescence. It was recorded at 25 °C and also at 45 °C, immediately after the respective time of 45 °c treatment of pea plants. Our results showed that when whole plants were exposed to 45 °C up to 24 h the CO2 assimilation and O2 evolution rate were more inhibited than the yield of primary photochemistry (estimated by the ratio Fv/Fm). 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.