VARIATION AMONG SPECIES IN THE TEMPERATURE-DEPENDENCE OF THE REAPPEARANCE OF VARIABLE FLUORESCENCE FOLLOWING ILLUMINATION

The relationship between the thermal dependence of the reappearance of chlorophyll variable fluorescence following illumination and temperature dependence of the apparent Michaelis constant (Km) of NADH hydroxypyruvate reductase for NADH was investigated in cool and warm season plant species. Brancker SF-20 and SF-30 fluorometers were used to evaluate induced fluorescence transients from detached leaves of wheat (Triticum aestivum L. cv TAM-101), cotton (Gossypium hirsutum L. cv Paymaster 145), tomato (Lycopersicon esculentum cv Del Oro), bell pepper (Capsicum annuum L. cv California Wonder), and petunia (Petunia hybrids cv. Red Sail). Following an illumination period at 25°C, the reappearance of variable fluorescence during a dark incubation was determined at 5°C intervals from 15°C to 45°C. Variable fluorescence recovery was normally distributed with the maximum recovery observed at 20°C in wheat, 30°C in cotton, 20°C to 25°C in tomato, 30 to 35°C in bell pepper and 25°C in petunia. Comparison of the thermal response of fluorescence recovery with the temperature sensitivity of the apparent Km of hydroxypyruvate reductase for NADH showed that the range of temperatures providing fluorescence recovery corresponded with those temperatures providing the minimum apparent Km values (viz. the thermal kinetic window).