The objective of the present work was to connect the nitrate reductase activity and the photochemical efficiency of the photosystem II (PSII), measured as F V/F M, in papaya (Carica papaya L.) cv. Tainung 01 and Sunrise Solo 72/12 in field conditions. The photochemical potential of PSII was measured in situ on attached leaves that had been dark adapted, prior to the fluorescence measurement. After, in same leaves, the enzyme activity was measured. There was not significant difference among the photochemical efficiency of PSII between cv. Tainung 01 and Sunrise Solo 72/12, even so, the activity of the enzyme was markedly higher in cv. Tainung 01 than in cv. Sunrise Solo 72/12. The nitrate redutase activity was highly correlated with the photochemical efficiency of the PSII in both cv. Tainung 01 (coefficient of correlation r= 0,740 and coefficient of determination r²= 0,706) and Sunrise Solo 72/12 (coefficient of correlation r= 0,960 and coefficient of determination r²= 0,945). These results suggest that there is a correlation between chlorophyll a fluorescence and nitrate reductase activity in these plants.
Carica papaya L.; chlorophyll a fluorescence; nitrogen metabolism
