Growth of Arabidopsis flavonoid mutants under solar radiation and UV filters

Growth of the chalcone isomerase defective tt-5 mutant of Arabidopsis thaliana and its Landsberg erecta progenitor were compared under a variety of full spectrum solar radiation conditions to determine if the tt-5 mutant could serve as an adequate subject for studies of the mechanisms of damage by UV-B radiation. An experiment was conducted in the fall of 1995 under open field filter frames using cellulose diacetate and Mylar filters to transmit and exclude natural UV-B irradiation, respectively. Even though growth under these conditions was slow and erratic owing to lack of temperature control, growth suppression as indicated by rosette diameter and harvest fresh weights provided a sensitive indicator of UV-B stress. This experience led to development of temperature-controlled Teflon-covered field chambers that admit up to 88% of the total daily PAR and about 85% of ambient UV-B, omit predators, and provide a generally stable environment for quantitative plant growth studies. The chambers were designed to facilitate the addition of optical filters and/or shade cloth and to accommodate control of the gaseous environment for pollutant and climate change studies and to provide clean air for other experiments. Three additional experiments were conducted in these chambers. Measurements of rosette diameter, weights of various aboveground plant parts, and plant height were evaluated as potential methods of comparing growth sensitivities of the tt-5 mutant to UV-B radiation. The weight of the reproductive parts (flowers and siliques) as a fraction of the total (e.g. harvest index) was consistently and negatively affected by solar UV-B, as was simple plant height. However, in no case, even in the virtual absence of UV-B, was growth of tt-5 comparable to that of Ler. We conclude that the disruption of secondary metabolism in tt-5 has growth implications far beyond the lack of UV-B protection, making it unsuitable as a surrogate for high UV-B experimentation.