Blue-green laser-induced fluorescence from intact leaves: actinic light sensitivity and subcellular origins

Remote sensing of the health status of vegetation should be possible by using UV laser-induced fluorescence; nevertheless, the molecular origin of the leaf blue-green fluorescence emission is still unknown. In order to investigate possible relations of this fluorescence to the photosynthetic apparatus, we looked for its intensity changes after the addition of actinic light. The lack of any changes outside the chlorophyll fluorescence bands (Kautsky effect) was further investigated by collecting spectra from cell, protoplast, and chloroplast suspensions. These spectra led us to ascribe most of the blue-green laser-induced fluorescence that is detectable on a leaf by UV laser excitation to extrachloroplastic compartments. In active chloroplast suspensions blue fluorescence from photosynthetically reduced nicotinamide adenine dinucleotide phosphate (NADPH) has been detected and should be characterized by time-resolved fluorescence techniques.