As the progenitors of seeds, ovules have a critical role in
plant sexual reproduction. An increased understanding of the
molecular genetic processes behind ovule development has the
potential to increase our ability to manipulate these processes
through either classical or molecular genetics. Characteristics such
as number of seed per fruit and nutritional quality of the seed are
candidates for modification. In addition to these potential agronomic
applications, ovules represent an excellent model system for plant
development. They are complex enough for their development to include
the major aspects of plant development, such as organogenesis,
differential cell division, cellular differentiation, and alterations
in gene expression. However, ovules are simple enough so that we have
a reasonable chance of elucidating all of the critical regulatory
steps necessary for their development.
This figure represents a series of stages in wild-type Arabidopsis ovule development. A) Stage 2-II (see Schneitz 1995 for stage descriptions); the inner integument has formed symmetrically, separating the nucellus from the funiculus. B) Stage 2-III; the outer integument has initiated proximal to the inner integument as a wedge of cells on the abaxial side. C) Stage 3-I; continued develop of both the inner and outer integuments, partially covering the nucellus. D) Stage 4-I (anthesis); the outer integuement has continued its asymmetric growth to completely cover both the inner integument and nucellus, leaving only the micropyle. E) Stage 4-I (anthesis); a pollen tube can be seen growing up the funiculus into the micropyle.
f, funiculus; ii, inner integument; m, micropyle; n, nucellus; oi, outer integument