Influence of supplementary LED lighting on physiological and biochemical parameters of tomato (Solanum lycopersicum L.) leaves

In modem tomato production, plant residues deliver an enormous amount of biomass including high-value components that so far are mainly unused. Especially the flavonol glycosid rutin has received stronger attention in recent research as a potentially health-promoting substance and due to its natural occurrence in tomato plants. In this study, tomato plants (cv. Lyterno) were grown in a commercial-like greenhouse and exposed to different lighting conditions. The objective of this work was to examine the influence of red (80%) and blue (20%) light-emitting-diodes (LEDs) (i) on rutin content in young and mature tomato leaves and (ii) on the physiological responses of tomato plants recorded with non-destructive sensor determinations. Our results revealed that supplementary LEDs induced the accumulation of secondary metabolites in tomato leaves grown in greenhouses such as higher rutin concentrations in young leaves and partly in mature leaves. A precise non-destructive estimation of rutin was not achieved but treatment-related differences in the fluorescence signals were clearly observed. Fluorescence-based recordings showed higher values for the Simple Fluorescence Ratio (SFR) as indicative of chlorophyll content, the Flavonol Index (FLAV) in young leaves and the Nitrogen Balance Index (NBI) in mature leaves. Even though a precise relationship between the FLAV index and the analytically determined rutin content could not be proven, clear clusters according to leaf age and day of leaf harvest were identified.