Different sites of photodamage in chilling-sensitive (sorghum) and chilling-resistant (barley and wheat) plants.

The electron transport chain was affected to varying degrees by high light intensity at low temperature in different crop plants. The PS II was found to be the sensitive site while PS I showed very little change in its activity. Photoinhibition affected the oxidizing side of PS II in all three plants. However, the site of inhibition was different in chilling-sensitive and chilling-resistant plants. In sorghum, the water splitting reaction was damaged while in barley and wheat the damage occurred in the reaction centre itself. It appears that photoinhibition may affect different sites within the PS II in chilling-resistant and sensitive plants.

Effect of water stress on primary photosynthetic process: interaction with light and temperature.

Effect of water stress alone and in combination with light and temperature on chlorophyll fluorescence and photosynthetic electron transport have been studied in drought-resistant wheat. It was observed that water stress alone-did not modify the amplitude of variable fluorescence in leaf but showed slight decrease in photosynthetic electron transport. However, interaction with light caused significant decrease in the efficiency of photosynthesis. This was greater when photoinhibited at 30 degrees C than at 10 degrees C. Results suggest that water stress alone does not lead to significant damage to the primary photochemistry but photoinhibition causes both inhibition of electron transport activity and chlorophyll fluorescence. The damage was further enhanced by the combination of water stress and high temperature.