Journal of Experimental Botany, Vol 50, 107-118, Copyright © 1999 by Oxford University Press
J Xia and A Kermode
Development of yellow cedar seeds is completed by about 17-21 months after
pollination. Following dispersal from the parent plant, the seeds exhibit a
low capacity for germination and typically require an additional year to
meet their moist chilling requirements and break dormancy. Biochemical
analyses were undertaken in order to address whether seed dormancy is
imposed and maintained because the embryo or megagametophyte is immature at
the time of seed shedding and hence requires time to complete developmental
events before dormancy can be terminated. Major protein reserves of the
embryo and megagametophyte are the buffer-insoluble crystalloid (legumin)
storage proteins and the water-soluble albumin proteins. SDS-PAGE,
fluorography of in vivo synthesized proteins and
Western blot analyses showed that the greatest increase in protein reserve
synthesis and accumulation occurred between the first and second years of
development; deposition of soluble and insoluble storage protein was
largely completed in seeds of second-year cones by August, 2-3 months prior
to seed dispersal. The period associated with greatest accumulation of
storage proteins was accompanied by an increased accumulation of two
ER-resident proteins associated with post-translational maturation of
storage proteins (binding protein and protein disulphide isomerase).
Accumulation of proteins implicated in the acquisition of desiccation
tolerance (dehydrins and the tonoplast intrinsic protein,
ARTICLES
Analyses to determine the role of embryo immaturity in dormancy maintenance of yellow cedar (Chamaecyparis nootkatensis) seeds: synthesis and accumulation of storage proteins and proteins implicated in desiccation tolerance
Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada V5A 1S6; Corresponding author; Fax: +1 604 291 3496; E-mail: kermode@sfu.ca
-TiP) occurred between the first and second years
of development. Several heat-stable proteins and some of the proteins
associated with late development continued to be synthesized after seed
shedding and in 13 d moist-chilled mature seeds. However, this did not
include the major dehydrin-like protein of yellow cedar seeds. Further, the
continued synthesis of heat-stable proteins does not appear to be a factor
preventing the germination of yellow cedar seeds following dispersal from
the parent plant; rather, the mechanism of dormancy is primarily
coat-imposed.Keywords: Embryo, megagametophyte, seed
development, yellow cedar, storage proteins, dehydrins, -TiP
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