Growth of Arabidopsis flavonoid mutants under solar radiation and UV filters

Growth of the chalcone isomerase defective tt-5 mutant of Arabidopsis thali ana and its Landsberg erecta progenitor were compared under a variety of fu ll spectrum solar radiation conditions to determine if the tt-5 mutant coul d serve as an adequate subject for studies of the mechanisms of damage by U V-B radiation. An experiment was conducted in the fall of 1995 under open f ield filter frames using cellulose diacetate and Mylar filters to transmit and exclude natural UV-B irradiation, respectively. Even though growth unde r these conditions was slow and erratic owing to lack of temperature contro l, growth suppression as indicated by rosette diameter and harvest fresh we ights provided a sensitive indicator of W-B stress. This experience led to development of temperature-controlled Teflon-covered field chambers that ad mit up to 88% of the total daily PAR and about 85% of ambient UV-B, omit pr edators, and provide a generally stable environment for quantitative plant growth studies. The chambers were designed to facilitate the addition of op tical filters and/or shade cloth and to accommodate control of the gaseous environment for pollutant and climate change studies and to provide clean a ir for other experiments. Three additional experiments were conducted in th ese chambers. Measurements of rosette diameter, weights of various abovegro und plant parts, and plant height were evaluated as potential methods of co mparing growth sensitivities of the tt-5 mutant to W-B radiation. The weigh t of the reproductive parts (flowers and siliques) as a fraction of the tot al (e.g. harvest index) was consistently and negatively affected by solar U V-B, as was simple plant height. However, in no case, even in the virtual a bsence of UV-B, was growth of tt-5 comparable to that of Ler. We conclude t hat 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. (C) 1999 Elsevier Science B.V. All rights r eserved.