THE PLANT CELL, Vol 3, Issue 6 605-618, Copyright © 1991 by American Society of Plant Biologists
Developmental and Environmental Induction of Lea and LeaA mRNAs and the Postabscission Program during Embryo Culture
D. W. Hughes and G. A. Galau
Department of Botany, The University of Georgia, Athens, Georgia 30602
The major programs of gene expression during late embryogenesis are the
maturation or reserve accumulation program and, after ovule abscission, the
postabscission program that is composed largely of Lea and LeaA mRNAs that
probably encode desiccation protectants. There are diverse opinions about
the developmental regulators of these programs. Several candidates are
evaluated here by measuring, in cultured embryos, the accumulation kinetics
of cloned mRNAs specifically expressed in the normal maturation,
postabscission, or germination programs of cotton. Maturation-stage embryos
both terminate the maturation program and induce the postabscission program
after excision and culture, just as they do later in the plant after ovule
abscission. However, they also induce simultaneously the germination
program and are thus different from any normal stage of embryo development
or germination. The developmental induction of the postabscission program
in culture does not require exogenous abscisic acid, but its expression is
enhanced by precocious desiccation or culture on abscisic acid or high
osmoticum, probably by an environmentally responsive mechanism that
normally operates during germination. Normal desiccation does not control
any of these programs because the embryo acquires all of the
characteristics of a mature embryo before it desiccates. These and other
results suggest regulation of normal embryogenesis by a maternal maturation
factor, a postabscission factor, and the postabscission program.
