Solar and supplemental UV-B radiation effects in lemon peel UV-B-absorbing compound content-seasonal variations.

Photochem Photobiol. 2008 Nov-Dec;84(6):1480-6. Epub 2008 May 29.

Hilal M, Rodríguez-Montelongo L, Rosa M, Gallardo M, González JA, Interdonato R, Rapisarda VA, Prado FE.

Cátedra de Fisiología Vegetal, Facultad de Ciencias Naturales e IML, UNT, Miguel Lillo, Tucumán, Argentina.

Effects of solar and supplemental UV-B radiation on UV-B-absorbing compounds and malondialdehyde (MDA) accumulations in the peel of lemons collected in summer and winter were analyzed. UV-B-absorbing compounds were higher in flavedo than in albedo tissue in both seasons; however, the highest values were observed in summer.

These compounds were also higher in outer than in inner flavedo surface. Lemons were categorized as sun-, semisun- and shaded-lemon according to localization inside the tree canopy. Depending on-tree localization UV-B-absorbing compounds were higher in flavedo of sun-lemon than in semisun- and shaded-lemon. Supplementary UV-B radiation (22 kJ m(-2) day(-1) UV-BBE) induced UV-B-absorbing compound synthesis in on-tree and postharvest lemons.

Two minutes of supplemental UV-B irradiation in summer lemons produced a strong increment (300%) of UV-B-absorbing compound content, whereas in winter lemons a slight increase (30%) was observed only after 3 min of irradiation.

By contrast, UV-B-absorbing compound accumulation was not observed in albedo. MDA accumulation showed approximately a similar trend of UV-B-absorbing compounds. According to our results, solar UV-B was not required for UV-B-absorbing compound accumulation in lemon peel. Relationships between UV-B-absorbing compounds, MDA, reactive oxygen species and pathogen protection are also discussed. PMID: 18513235