0023-6152

AA00697606

4561

Unrefereed

0023-6152

AA00697606

Carbon dioxide gas exchange rate (CER), stomatal conductance (Gs), and photosystem Ⅱ quantum yield (Φe) were measured with three C4 subtype plants, corn (Zea mays L., NADP-ME type), common millet (Panicum miliaceum L., NAD-ME type), guineagrass (Panicum maximum Jacq., PEC-CK type) and a C3 type plant, mung bean (Vigna radiata L.) grown in droughts. The specific difference in drought tolerance in photosynthesis was discussed in relation to their photorespiratory activity. The C4 plants were superior to mung bean in both photosynthetic sustainability in droughts and photosynthetic recovery under re-watering after droughts. CER and Φe of corn showed a large reduction with a lanient decrease ni leaf water potential (ΨL) compared to those of the other two subtypes. In both guineagrass and common millet Φe was sustained at a relatively higher level when their CER was decreased in droughts. A similar specific feature to this was found in leaves measured in the air with low CO2 concentrations. This may suggest that there is ans inter-subtype difference in photorespiration activity. Having a higher photorespiration activity is regarded as a cause for guineagrass and common millet to have superiority in drought torelance. The inter-subtype dofference in photorespiration activity was also able to be estimated from Φe of film-sealed leaves.