Responsiveness of Lycopersicon pimpinellifolium to acute UV-C exposure: histo-cytochemistry of the injury and DNA damage

The in vivo and in vitro effects of UV-C (254 nm) exposure (0.039 watt · m-2 · s for 2 h) of currant tomato (Lycopersicon pimpinellifolium), indigenous to Peru and Ecuador, were assayed. H2O2 deposits, dead cells and DNA damage were localized, 12/24 h after irradiation, mainly in periveinal parenchyma of the 1st and 2nd order veins of the leaves, and before the appearance of visible symptoms, which occurred 48 h after irradiation. Cell death index was of 43.5 ± 12% in exposed leaf tissues, 24 h after treatment. In currant tomato protoplasts, the percentage of viable cells dropped 1 h after UV-C irradiation from 97.42 ± 2.1% to 43.38 ± 4.2%. Afterwards, the protoplast viability progressively decreased to 40.16 ± 7.25% at 2 h, to 38.31 ± 6.9% at 4 h, and to 36.46 ± 1.84% at 6 h after the exposure. The genotoxic impact of UV-C radiation on protoplasts was assessed with single cell gel electrophoresis (SCGE, or comet assay). UV-C treatment greatly enhanced DNA migration, with 75.37 ± 3.7% of DNA in the tail versus 7.88 ± 5.5% in the case of untreated nuclei. Oxidative stress by H2O2 used as a positive control, induced a similar damage on non-irradiated protoplasts, with 71.59 ± 5.5% of DNA in the tail, whereas oxidative stress imposed on UV-C irradiated protoplasts slightly increased the DNA damage (85.13 ± 4.1%). According to these results, SCGE of protoplasts could be an alternative to nuclei extraction directly from leaf tissues.