Ovary and Gametophyte Development are Coordinately Regulated Following
Pollination by Auxin and Ethylene
X. S. Zhang and S. D. O'Neill
The Plant Cell 5:403-418 (1993)
ABSTRACT
The differentiation and development of ovules in orchid flowers is a
pollination-dependent developmental event. To define the developmental signals
and timing of critical events associated with ovule differentiation, we have
examined factors that regulate the initial events in megasporogenesis and
female gametophyte development and characterized its progression towards
maturity and fertilization. Two days after pollination, ovary wall epidermal
cells begin to elongate and form hair cells; this is the earliest visible
morphological change and occurs at least three days prior to pollen germination
indicating that signals associated with pollination itself trigger these early
events. The effects of inhibitors of ethylene biosynthesis on these early
morphological changes indicated that ethylene, in the presence of auxin, is
required to initiate ovule differentiation. Surprisingly, pollen germination
and growth were also strongly inhibited by inhibitors of ethylene biosynthesis
indicating that male gametophyte development is also regulated by ethylene.
Detailed characterization of the development of both male and female
gametophyte development in pollinated orchid flowers indicated that pollen
tubes entered the ovary and grew along the ovary wall for 10 to 35 days before
growth was arrested. At approximately 40 days after pollination, conincident
with ovule differentiation as indicated by the presence of a single
archesporial cell, the direction of pollen tube growth became redirected
towards the ovule. Taken together, these results indicate that both auxin and
ethylene play major roles in initiating both ovary and ovule development and
coordinating the development of the male and female gametophytes, and that the
coupling of pollen tube growth to ovule maturation at later stages may be
regulated by other chemical signals.