Antarctic plants experience UV−B stress and for their survival they have been showing various adaptive strategies. The first line of defence is to screen UV−B radiation before it reaches the cell, then to minimize damage within the cells through other protective strategies, and finally to repair damage once it has occurred. A fifteen days experiment was designed to study lichen: Dermatocarpon sp. and Acarospora gwynnii under natural UV and below UV filter frames in the Indian Antarctic Station Maitri region of Schirmacher Oasis, East Antarctica. Changes in UV absorbing compounds, total phenolics, total carotenoids and chlorophyll content were studied. The change in total phenolics and total carotenoid content was significant in both Dermatocarpon sp. and A. gwynnii indicating that the increase in UV absorbing compounds, total phenolics and total carotenoid content act as a protective mechanism against the deleterious effect of UV−B radiations, whereas the change in chlorophyll content was not significant in both lichen species.
This study examined the effects of UV-B radiation and allelochemical stress induced by ferulic acid (FA) on the activity of phenylalanine ammonia lyase (PAL; EC 188.8.131.52) at metabolic and molecular levels in two cucumber genotypes differing in tolerance to cold and disease, in order to determine any interaction between stress effects and genotype response. Stresses were applied simultaneously, sequentially, and singly. In both genotypes, several days of UV radiation retarded growth up to 36%. The effect of FA was not significant. The response to a particular stress, including the effect on PAL activation, was enhanced by simultaneous application of the two stresses. PAL transcription was not correlated with the increase of PAL activity. Exposure to UV-B, FA, and combined UV-B and FA was detrimental to both genotypes but to different extents. The response was not correlated with the genotype of cold and disease sensitivity. PAL activity and its transcription seem to be involved in UV and allelochemical stress, but not related to the plants' tolerance of these stresses.