Photorespiration Rate in Mungbean (Vigna radiata (L.) Wilczek) Leaves - A further estimation from the quantum yield at photosystem II.

Photorespiration rates (PR) in peeled (PL, without epidermis) and nonpeeled (NL) leaves of mungbean (Vigna radiata. (L.) Wilczek) were estimated from electron transport situations at photosystem II using the chlorophyll fluor escence quenching diagnosis. The number (k(1)) of electron equivalents requ ired to produce 9 mol adenosine 5'-triphosphate (ATP) for fixing 1 mol CO2 was experimentally determined 4.62. Also the number (k(2)) of electrons req uired for releasing 1 moi CO2 in photorespiration was estimated 7.44 or 9.4 9 on the assumption that 14.5 or 18.5 mol ATP was consumed for 1 mol CO2 re leasing, respectively. The simultaneous equations were constructed with the parameters of k(1), k(2) and related elements to calculate PR, and the mut ual relationships in energy balance among PR, gross photosynthetic rate (Pg ), total photosynthetic rate (TC, TC=PR+Pg) and PR ratio (PR/TC) were discu ssed. The value of PR, 1.75 or 2.05 mu mol m(-2) s(-1), in PL was estimated corresponding to k(2)=7.44 or 9.49 in a light intensity of 300 mu mol m(-2 ) s(-1) PPFD, and PR/TC was 18.2 or 20.6%, respectively. The estimation by chlorophyll fluorescence quenching diagnosis may give a more reasonable val ue of PR as compared with the PR obtained by the subtraction method (PR=Pg measured in 2% [O-2] air Pg measured in 2% [O-2] air).