PLANT PHYSIOLOGY , Vol 110, Issue 4 1109-1121, Copyright © 1996 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Hormonal Studies of fass, an Arabidopsis Mutant That Is Altered in Organ Elongation
R. H. Fisher, M. K. Barton, J. D. Cohen and T. J. Cooke
Department of Plant Biology, University of Maryland, College Park, Maryland 20742-5815 (R.H.F., T.J.C.)
We have isolated an allele of fass, an Arabidopsis thaliana mutation that
separates plant development and organ differentiation from plant
elongation, and studied its hormonal regulation. Micro-surgically isolated
fass roots elongate 2.5 times as much as the roots on intact mutant plants.
Wild-type heart embryos, when cultured with a strong auxin,
naphthaleneacetic acid, phenocopy fass embryos. fass seedlings contain
variable levels of free auxin, which average 2.5 times higher than
wild-type seedling levels, and fass seedlings evolve 3 times as much
ethylene as wild-type seedlings on a per-plant basis over a 24-h period.
The length-to-width ratios of fass seedlings can be changed by several
compounds that affect their endogenous ethylene levels, but fass is
epistatic to etr1, an ethylene-insensitive mutant. fass's high levels of
free auxin may be inducing its high levels of ethylene, which may, in turn,
result in the fass phenotype. We postulate that FASS may be acting as a
negative regulator to maintain wild-type auxin levels and that the mutation
may be in an auxin-conjugating enzyme.
