Influence of UV radiation on the content of secondary metabolites in tomato grown in different environmental conditions

Abstract

In this study we investigated the effects of ambient ultraviolet (UV, 280- 400 nm) radiation on the composition of secondary metabolites of high nutritional value (pigments and flavonoids) in Lycopersicon esculentum (tomato) fruits. Tomato plants were grown during summer in the open field and two types of polytunnels, PT1 ( UV-A 1.45 mV cm-2, UV-B 3.84 μV cm-2, PAR 750 μmol m-2 s-1) and PT2 (UV-A 0.37 mV cm-2, UV-B 0.03 μV cm-2, PAR 760 μmol m-2 s-1) and fruits were taken in august. The contents of lycopene, β-carotene and flavonoids (quercetin and kaempferol) were determined by HPLC in the tomato exocarp and pulp. Regardless of UV radiation exposure, higher amounts of lycopene, flavonoids and β-carotene were measured in exocarp compared to the pulp. Accumulation of phenolics, in both exocarp and pulp was the highest in fruits collected in the field. Similarly, the concentration of epidermal flavonoids was the highest in the leaves of plants from the open field. These results support the protective functions of flavonoids as UV-screeners and antioxidants from high PAR. Moreover, the content of lycopene was the highest in exocarp and β-carotene in the pulp of fruits exposed to full ambiental UV radiation doses, compared to fruits collected in the polytunells. The results implicate that the controlled exposure to solar UV radiation during crop growth may be used as a stimulator of biosynthesis of compounds with high antioxidative capacity thus improving the fruit quality and nutritional value.