Remote and Near-Contact Chlorophyll Fluorescence during Photosynthetic Induction in Iron-Deficient Sugar Beet Leaves

A comparison of time-resolved, laser-induced remote sensing and pulse amplitude modulation near-contact techniques has been carried out during photosynthetic induction in iron-deficient sugar beet leaves. Iron deficiency caused increases in the mean chlorophyll fluorescence lifetime. These increased chlorophyll fluorescence lifetimes occurred in dark-adapted leaves, during a sudden increase in light intensity and also at steady-state photosynthesis. Chlorophyll fluorescence lifetimes were correlated with the extent of nonphotochemical and/or photochemical quenching. During most of the photosynthetic induction period, Fe-deficient leaves showed lower actual PSII efficiencies than control leaves, due to decreases in photochemical quenching and intrinsic PSII efficiency. During photosynthetic induction Fe deficiency decreased the proportion of light absorbed by the PSII antenna that is used in photochemistry and increased the proportion dissipated thermally within the PSII antenna, the later being well correlated with nonphotochemical quenching. Laser instrumentation offers new perspectives for monitoring effects of stress conditions in plants at large spatial scales.