CHARACTERIZATION OF BLUE-GREEN FLUORESCENCE IN THE MESOPHYLL OF SUGAR-BEET (BETA-VULGARIS L) LEAVES AFFECTED BY IRON-DEFICIENCY

The mesophyll of sugar beet (Beta vulgaris L.) leaves emits red (chror ophyll a) fluorescence and blue-green fluorescence when excited with u ltraviolet light. The intensity of blue-green fluorescence was increas ed in mesophylls affected by iron deficiency. This increase was large and progressive. It was concomitant with a decrease of photosynthetic pigments per unit of leaf area. Most of the increase in blue-green flu orescence can be explained by the decrease of the screening of ultravi olet light by chlorophylls and carotenoids. In addition, chlorophylls selectively reabsorb blue fluorescence, which leads to a change in the form of the fluorescence emission spectra. This effect induces an inc rease of the blue-to-green fluorescence ratio in control mesophylls th at was concomitant with the decrease of chlorophyll per unit of leaf a rea. Iron deficiency induced a decrease of the blue-to-green fluoresce nce ratio that may be attributed to an accumulation of flavins fluores cing in the green. Time-resolved fluorescence measurements indicate th at they are mostly riboflavin and/or flavin mononucleotide phosphate. Our data also indicate that the blue-green fluorescence emitted from t he mesophyll contains fluorescence of nicotinamide nucleotides.