XVI International Botanical Congess

The literature on phototropism shows many controversies, perhaps largely reflecting its mechanistic complexity. I will discuss some basic physiological issues, introducing our recent results from coleoptiles (Avena sativa and Zea mays) and stems (Pisum sativum). Included are (1) the spatial separation between the photoreception and curvature response, (2) the validity of the Cholodny-Went theory, and (3) the contribution of autotropic straightening. I will also discuss the ubiquitous occurrence of the negative phototropism by primary roots. Finally our results from Oryza sativa seedlings are introduced. We have isolated a mutant that shows no phototropism by coleoptiles and severely impaired phototropism by roots. In this mutant, growth and gravitropism are normal, and the genes homologous to CRY1 and NPH1 are expressed normally.