Simultaneous CO2- and O-16(2)/O-18(2)-gas exchange and fluorescence measurements indicate differences in light energy dissipation between the wild type and the phytochrome-deficient aurea mutant of tomato during water stress

The CO2-, H2O- and O-16(2)/O-18(2) isotopic-gas exchange and the fluorescence quenching by attached leaves of the wild-type and of the phytochrome-deficient tomato aurea mutant was compared in relation to water stress and the photon fluence rate, The chlorophyll content of aurea leaves was reduced and the ultra-structure of the chloroplasts was altered, Nevertheless, the maximum rate of net CO2 uptake in air by the yellow-green leaves of the aurea mutant was similar to that by the dark-green wild-type leaves, However, less O-2 was produced by the leaves of the aurea mutant than by leaves of the wild-type, This result indicates a reduced rate of photosynthetic electron flux in aurea mutant leaves, No difference in both photochemical and nonphotochemical fluorescence quenching was found between wild-type and aurea mutant leaves, Water stress was correlated with a reversible decrease in the rates of both net CO2 uptake and transpiration hy wild-type and aurea mutant leaves, The rate of gross O-16(2) evolution by both wild-type and aurea mutant leaves was fairly unaffected by water stress, This result shows that in both wild-type and aurea leaves, the photochemical processes are highly resistant to water stress, The rate of gross O-18(2) uptake by wildtype leaves increased during water stress when the photon fluence rate was high, Under the same conditions, the rate of gross O-18(2) uptake by aurea mutant leaves remained unchanged. The physiological significane of this difference with respect to the (presumed) importance of oxygen reduction in photoprotection is discussed.