Photosynthetic performance of Vigna radiata L . lea v es de v eloped at different temperature and irradiance le v

The photosynthetic performance of mungbean (Vigna radiata L.) leaves developed at (1) 30/25 8C /700 PFD (LT /HI), (2) 40/ 25 8C /700 PFD (HT /HI), and (3) 40/25 8C /200 PFD (HT /LI) was evaluated. Photosynthetic CO2 assimilation rate (Pn) and different Chl a fluorescence parameters of those leaves were measured at different temperatures and photon flux density (PFD). Pn of the LT /HI-developed leaves continued to increase till 2000 PFD while the Pn was lower in the leaves developed at high temperature. HT /HI-developed leaves showed higher Pn than that developed at the same temperature but with low light (HT /LI). Rapid light curves revealed that leaves developed at high light had better photosynthetic efficiency at fast changing light environment than those developed at low light irrespective of their growth temperatures. LT /HI-plants had the highest photochemical quenching (qP) as well as non-photochemical quenching (qN) compared to the plants developed at high temperature (HT /HL and HT /LI). Heat acclimation in the presence of high light appreciably protected the activity of photosynthetic apparatus from heat shock-damage. This was disclosed with the higher photosynthetic efficiency of HT /HI-grown plants after heat shock treatment up to 55 8C than the plants developed at the same temperature but with low light. Leaves developed at HT /LI showed severe photoinhibition of photosynthesis when exposed to strong light for 9 h and did not recover appreciably from the damage compared to those developed at high light (LT /HI and HT /HI). From the various Chl a fluorescence parameters that we determined it would appear that high light exposure protects efficiently the photochemical activity of leaf against its inactivation by heat compared to low light exposure. # 2002 Published by Elsevier Science Ireland Ltd.