Blue light sensitivity of UV-irradiated young sporophytes of Laminaria hyperborea

Abstract

After damaging UV irradiation (wavelength 253.7 nm), subsequent exposure to visible light enhanced survival of young sporophytes of Laminaria hyperborea. This photoreactivation was wavelength-dependent, showing significant recovery in blue light compared with no measurable recovery either in green or red light. In white light, the effect was proportional to irradiance until saturated at ≈ 35 μmol m −2 s −1. After 12 h of various types of irradiation (10 μmol m −2 s −1 of coloured light or darkness) followed by 12 h white light (35 μmol m −2 s −1), the survival percentage of plants in 12 : 12 blue: white light was almost the same as that in continuous white light. In other cases, it was half that in continuous light. If the photoreceptor for photoreactivation were identical with that for 2-D growth of Scytosiphon lomentaria, the relative effectiveness of waveband 400–500 nm would be 3.4 times as great in blue light as in white light. In direct comparisons, when white irradiance was 3.5 times blue, survival percentages in 24 h blue, 12 : 12 blue:white and 24 h white light were found to be similar, indicating a likely involvement of the same photoreceptor. The quantum requirement of the plant for a 50% response was comparable to that for other blue light responses found in brown algae.