Evidence Inconsistent with the Blaauw Model of Phototropism

Abstract

The Blaauw model of phototropism equates the inhibition of growth at the illuminated side of a unilaterally illuminated organ with the blue light inhibition of overall organ extension evident when some shoots are exposed to uniform blue light However, a study of the growth responses of Avena coleoptiles exposed to omnilateral, equal bilateral, unequal bilateral and unilateral blue light has revealed some light induced growth rate changes which cannot be explained by the Blaauw model. The growth responses of cells at the illuminated and shaded sides of phototropically stimulated coleoptiles seem to depend on the existence of a light gradient across the whole organ rather than the absolute levels of light at either side.