Integration and scaling of UV-B radiation effects on plants: From DNA to whole plant

Background/Question/Methods

Integration and scaling among various levels of organization and ecological processes are inherent in ecology and pose major challenges in understanding the consequences of global environmental problems. Although integrative ecological research becomes more prevalent, many ecological studies still have limited ecological relevance as complexity and scale increases, and fail in testing the major natural world theories. Ultraviolet radiation has been a natural environmental stress factor for organisms since the pre-Cambrian era. While UV radiation induces mostly molecular level injuries, they result in direct effects on the whole plant growth, resource allocation, and reproduction, and indirect effects on the community structure and function. Several decades of experimental research on this problem has been mostly limited to individual and sub-individual plant levels, mainly due to the technical difficulties in simulating an enhanced UV-B radiation regime at the scales required for higher ecological-level experiments.

A process based model, integrating the pathway of UV-B radiation from epidermis to DNA, its effects on metabolism and photosynthesis, and its consequences to organs and whole plant biomass, was used to understand plant response mechanisms to UV-B radiation and their broader consequences, as well as to investigate hypotheses that were untestable by experimental research. 

 Results/Conclusions

Enhanced UV-B radiation-induced DNA damage significantly delayed cell division until the injury is repaired, resulting in significant reductions in plant growth and development. Species with high relative epidermal absorbance at longer wavelengths and average and low pyrimidine cyclobutane dimers (CPD) photorepair rates exhibit reductions in growth even at ambient UV-B radiation levels.  Simulations indicated that leaf expansion, thus photosynthetic capacity was highly dependent on the number of CPD present in the DNA, as a result of UV-B dose, quantitative and qualitative absorptive properties of epidermal pigments, and repair mechanisms. Formation of pyrimidine-pyrimidone (6-4) photoproducts has no effect on the plant growth and development. Our model showed that repair mechanisms cannot solely prevent the UV-B radiation interference with the cell division. Avoidance or effective shielding by increased or modified qualitative epidermal absorptance is required. Long, sustained increased UV-B radiation levels are more detrimental than short, high doses of UV-B radiation. Therefore, slow growing plants were more affected by increased UV-B radiation than fast growing plants. The combination of low temperature and increased UV-B radiation was more significant in the level of UV-B radiation induced damage than UV-B radiation alone.