UV-A/blue light-induced reactivation of photosynthesis in UV-B irradiated cyanobacterium, Anabaena sp.

After exposure to moderate levels of UV-B irradiation, subsequent exposure to white light caused recovery of chlorophyll fluorescence yield of Anabaena sp. This photoreactivation of UV-induced inhibition of photosynthesis increased in proportion to the irradiance of white light and is wavelength-dependent, showing significant recovery in blue light compared to no measurable recovery at other photosynthetically active wavebands. The UV-A/blue quantum dose required for a 50 % photoreactivation was 1.12 mol m−2, which is comparable to that for other high quantum requiring responses found in plants and microorganisms. Additionally, a similar long-term interdependence is reflected in the observation that the effect of UV-A/blue light depends on the total quantum exposure for up to 96 h, confirming the likely involvement of a blue light receptor, cryptochrome, in this process. The action spectrum for photoreactivation of photosynthesis in UV-B-irradiated Anabaena sp. shows major peaks at 352.5 and 383 nm, with a small but significant peak at 411 nm.