Photosynthetic rate (P), leaf water potential (psi(L)) and chlorophyll fluorescence were studied in mungbean plants subjected to waterlogging in a plastic greenhouse, and leaf samples were collected for the analysis of enzymes involved in anti-oxidant photoprotection. Waterlogging caused a fast decline in the photosynthetic rate and water use efficiency without changes of transpiration rate and stomatal conductance during the early waterlogging period, which indicates that reduction of photosynthetic rate might be due to a mechanism independent from stomatal closure. Early reduction of Fv/Fm value of chlorophyll fluorescence by waterlogging indicates that the early reduction of photosynthetic rate is correlated with photo inhibition of photosystem II (PSII). Stomatal conductance and water use efficiency was decreased progressively during prolonged waterlogging while psi(L) was unchanged, indicating stomatal closure without water stress. The activities of active oxygen processing enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) decreased during prolonged waterlogging indicating no evidence of oxidative stress and/or damage in leaves of mungbean by waterlogging. Our results suggest that oxidative damage is not directly involved in damage to the photosynthetic machinery during waterlogging in mungbean plants. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.
