PLANT PHYSIOLOGY , Vol 105, Issue 4 1433-1436, Copyright © 1994 by American Society of Plant Biologists
Light-Stimulated Cotyledon Expansion in the blu3 and hy4 Mutants of Arabidopsis thaliana
D. E. Blum, M. M. Neff and E. Van Volkenburgh
Department of Botany AJ-30, University of Washington, Seattle, Washington 98195
Cotyledon expansion in response to blue light was compared for wild-type
Arabidopsis thaliana (L.) Heynh. and the mutants blu3 and hy4, which show
reduced inhibition of hypocotyl growth in blue light. White, blue, and red
light stimulated cotyledon expansion in both intact and excised cotyledons
of wild-type seedlings (ecotypes No-0, WS, Co-0, La-er). Cotyledons on
intact blu3 and hy4 seedlings did not grow as well as those on the wild
type in response to blue light, but pretreatment of blu3 seedlings with low
fluence rates of red light increased their responsiveness to blue light.
Excision of cotyledons alleviated the mutant phenotype so that both mutant
and wild-type cotyledons grew equally well in blue light. The loss of the
mutant cotyledon phenotype upon excision indicates that the blu3 and hy4
lesions affect cotyledon expansion indirectly via a whole-plant response to
light. Furthermore, the ability of excised, mutant cotyledons to grow
normally in blue light shows that this growth response to blue light is
mediated by a photosystem other than the ones impaired by the blu3 and hy4
lesions.
