UV-absorbing pigments, photosynthesis and UV exposure in Antarctica: comparison of terrestrial and marine algae

Abstract

Since Antarctic plants experience a wide range of ultraviolet (UV) exposure, the pigment content of Antarctic algae ( Palmaria decipiens (Reinsch) Ricker, Enteromorpha bulbosa (Suhr) Montagne, Prasiola crispa (Lightf.) Kütz. sp. antarctica (Kützing) Knebel) was monitored over a year. In summer the mature form of the marine rhodophyte Palmaria contains a range of UV-absorbing pigments in high concentration providing a broad absorbance with a maximum at 337 nm. Juvenile fronds develop through winter with smaller absorbance maxima at 322 nm, 309 nm and 295 nm. The terrestrial chlorophyte Prasiola crispa contains a single UV-absorbing pigment with a maximum at 325 nm. Compared with other green algae, including the marine Enteromorpha, the UV-absorbing pigment in Prasiola is present in high concentrations. Variations in the level of UV-absorbance relative to chlorophyll in Prasiola, appear to correspond with varying UV exposure. To test this, Prasiola was maintained with an enhanced ratio of UV-B to visible light to simulate the effects of stratospheric ozone depletion. After 4 weeks the chlorophyll content and photosynthetic rates were reduced in the presence of enhanced UV-B light, but the ratio of UV-absorbing pigments to chlorophyll was unchanged. This suggests that even for Antarctic algae, that contain high levels of UV-absorbing pigments, exposure to sunlight with an increased ratio of UV-B to visible light is stressful.