Causal relationship between growth inhibition, accumulation of phenolic metabolites, and changes of UV-induced fluorescences in nitrogen-deficient barley plants

Abstract

UV-induced chlorophyll (ChlFUV) and blue-green (BGF) fluorescences emitted by leaves have been proposed as useful indicators of plant physiological status under stress conditions. In this report, we investigated the effects of nitrogen (N) deficiency on ChlFUV and BGF emissions of leaf sections in relation to plant growth inhibition and accumulation of phenolic metabolites in barley leaves. Plants in a growth chamber were supplied with one of five different NO3 concentrations (0.8, 1.6, 5.0, 8.0, or 16 mmol/L) for a 2-week period. Total fresh biomass decreased with decreasing N supply, whereas leaf content of soluble phenolic compounds increased. This increase in leaf phenolic compounds observed with limiting N supply was accompanied by large increases of the BGF intensity and BGF/ChlFUV ratio of leaf sections and, to a lower extent, by a decrease of the leaf epidermal transmittance of UV radiation (as estimated by the ratio of ChlF intensities induced by UV and blue excitation). Interestingly, we observed a negative correlation (r2 = –0.975) between fresh biomass of plants and BGF intensity of leaf sections. By interpreting, in a context of stress physiology, the changes of UV-induced fluorescences, our results support their potential use as a sensitive tool for the rapid assessment of a plant's nutrient status.Key words: blue-green fluorescence, chlorophyll fluorescence, flavonoids, growth inhibition, nitrogen deficiency, phenolic compounds.