Effects of leaf epidermis peeling on the CO2 exchange rate and chlorophyllfluorescence quenching, and estimation of photorespiration rate from electron transport in mungbean (Vigna radiata (L.) Wilczek) leaves.

CO2 gas exchange rates (CER) in a peeled leaf (PL) and nonpeeled leaf (NL) of mungbean (Vigna radiata (L.) Wilczek) were measured in a saturating ligh t intensity to identify their responses to CO2 concentrations ([CO2]) and l eaf temperatures. The CER of PL was regarded as an indicator for the photos ynthetic potential in mesophyll. When measured at 35 degrees C, CER was enh anced by peeling the epidermis, whereas it was less effective at 25 degrees C and almost not effective at 15 degrees C. In [CO2]-CER response curves, CER of PL had a highest plateau in 500 to 1,000 mu molmol(-1) [CO2] at 35 d egrees C, whereas at both 25 and 15 degrees C CER showed a peak in 500 mu m olmol(-1) [CO2]. When measured in the air of 20% O-2 concentration ([O-2]) in a light intensity of 300 mu molm(-2)s(-1) photosynthetically photon flux density (PPFD) at 25 degrees C, the CO2 quantum yield (Phi(CO2)) in PL was higher than that in NL, whereas the photosystem II (PSII) quantum yield (P hi(e)) was a little lower in FL. The number (k) of electron equivalents req uired to fix 1 mol CO2 was greatly increased in NL due to the increased pho torespiration. Tn 2% [O-2] k of PL was 4.62, which was a little larger than a theoretical minimum (k=4). From the relationships between k, CER and ade nosine 5'-triphosphate (ATP) required for photosynthesis, the rates of phot orespiration were estimated in different environments.