Journal of Experimental Botany, Vol 49, 1317-1327, Copyright © 1998 by Oxford University Press
L Egerton-Warburton
Emmenanthe penduliflora is an obligate fire-recruiter
and demonstrates a prolonged seed dormancy followed by germination closely
cued to the immediate post-fire environment. This study investigated, at
the ultrastructure level, the causal factor(s) associated with seed
dormancy and the stimulation of germination after exposure to smoke. The
seed coat was responsible for the proximal regulation of dormancy - a waxy
cuticular layer situated between the testa and endosperm was the primary
barrier to the diffusion of water and small diameter solutes. The sub-testa
cuticle in dormant seeds was partially permeable, as indicated by the
presence of permeate channels. A short exposure to dry smoke (3 min)
promoted a significant increase in seed germination (dormant 8
ARTICLES
A smoke-induced alteration of the sub-testa cuticle in seeds of the post-fire recruiter, Emmenanthe penduliflora Benth. (Hydrophyllaceae)
Department of Botany and Plant Sciences, The University of California, Riverside, CA 92521-0124, USA; Present address: School of Botany, The University of Melbourne, Parkville 3052, Victoria, Australia
0.3% smoke-treated 793%). Exposure to smoke also resulted in two major
changes to the morphology of the seed. First, smoke treatment produced an
intense chemical scarification at the seed surface; the external cuticle
was plasticized to form numerous small spheres on the seed surface. Second,
smoke significantly altered the permeability of the internal (sub-testa)
cuticle. A significant increase in both the number and size of permeate
channels in the sub-testa cuticle indicated that these modifications were
directly associated with the breaking of seed dormancy. The observed
changes at both the internal (sub-testa) and external cuticles are
consistent with the hypothesis that volatiles in smoke exert a
surfactant-like reaction to break seed dormancy in E.
penduliflora.Keywords: Emmenanthe
peduliflora, smoke, fire-recruiter, chaparral, seed coat
dormancy
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