Effects of leaf epidermis peeling on the CO2 exchange rate and chlorophyll fluorescence quenching, and estimation of photorespiration rate from electron transport in mungbean (Vigna radiata (L.) Wilczek) leaves
1999
Tokuda, S. (Kyushu Univ., Fukuoka (Japan)) | Kubota, F. | Hirao, K. | Saitou, K.
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 light intensity to identify their responses to COB concentrations ([CO3]) and leaf temperatures. The CER of PL was regarded as an indicator for the photosynthetic potential h mesophyll. When measured at 35 degrees C, CER was enhanced 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-molmo1(-1) [CO2] at 35 degrees C, whereas at both 25 and 15 degrees C CER showed a peak in 500 mu-molmol(-I) [CO2l. When measured in the air of 20% O2 concentration ([O2]) in a light intensity of 300 mu-mol m(-2)s(-1) photosynthetically photon flux density (PPFD) at 25 degrees C, the COB quantum yield (Phi(CO2)) in PL was higher than that in NL, whereas the photosystem II (PSII) quantum yield (Phi(e)) was a little lower in PL. The number (k) of electron equivalents required to fix 1 mol CO2 was greatly increased in NL due to the increased photorespiration. In 2% [O2] k of PL was 4.62, which was a little larger than a theoretical minimum (k=4). From the relationships between k, CER and adenosine 5'-triphosphate (ATP) required for photosynthesis, the rates of photorespiration were estimated in different environments
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