REACTION NORMS OF ARABIDOPSIS .1. PLASTICITY OF CHARACTERS AND CORRELATIONS ACROSS WATER, NUTRIENT AND LIGHT GRADIENTS

The univariate and multivariate study of variation for phenotypic plas ticity is central to providing a clear understanding of hypotheses abo ut the genetic control and evolution of reaction norms in natural popu lations. Arabidopsis thaliana is an ideal organism for the study of Ge notype x Environment interactions (i.e., genetic variation for plastic ity), because of the ease with which it can be grown in large numbers and due to the amount of information already available on its genetics , physiology and developmental biology. In this paper, we report on th e plasticity, genetic Variation and G x E interactions of four populat ions of A. thaliana in response to three environmental gradients (wate r, light and nutrients), each characterized by four levels of the cont rolled parameter. We measured nine traits and obtained their reaction norms. Path analysis was used to study the plasticity of character cor relations. We found a tendency for A. thaliana reaction norms to be li near (either flat, i.e. no plasticity, or with a significant slope), i n accordance with previous studies. We detected substantial amounts of genetic variation for plasticity in the light and nutrient gradients, but not in the water gradient. Dramatic restructuring of character co rrelations was induced by changes in environmental conditions, althoug h some paths tended to be stable irrespective of the environment, ther eby suggesting some degree of canalization.