Plant growth, development, and environmental responsiveness are
dependent on hormone-induced gene expression. This dissertation reports
multiple interactions between the plant hormones auxin and ethylene and
investigates their contribution to the gravitropic response, elongation
growth, adventitious root formation, callus and tracheary element initiation
and growth, and flower development.
Four mutants of tomato (Lycopersicon esculentum, Mill.) altered in
either hormone production or hormone response were used to test the
involvement of ethylene and auxin. These mutants included diageotropica
(dgt) which is auxin-resistant, Never-ripe (Nr), which is ethylene-resistant,
epinastic (epi), which overproduces ethylene and lazy-2 (lz-2), which
exhibits a phytochrome-dependent reversed-gravitropic response.
Additionally, a double mutant between Nr and dgt was constructed and
tested.
Gravitropism was studied as an exemplary process involving both
auxin and ethylene. Mutant analysis demonstrated that ethylene does not
play a primary role in the gravitropic response via the currently known
ethylene response pathways. However, ethylene can modify the gravitropic
response, e.g. the delayed gravitropic response of the dgt mutant can be
restored with exceedingly low concentrations of ethylene and ethylene
synthesis- and ethylene-action inhibitors can partially inhibit the
graviresponse.
The role of gravity in tracheary element (TE) production was tested
in microgravity (during a space shuttle flight) and in hypergravity
(centrifugation). A correlation was found between gravitational force and the
production of TEs, with decreased numbers of TEs produced in
microgravity and increased numbers produced in response to hypergravity.
Increased production of TEs by dgt in both increased and reduced gravity
indicates that gravity regulates vascular development via a DGT-dependent
pathway involving auxin.
Combination of both the Nr and dgt mutations in a double mutant
leads to plants which exhibit the reduction of auxin-sensitivity typical of dgt
as well as a delay in fruit ripening typical of Nr. The reduced gravitropic
response of the dgt mutant was restored to wild-type levels in the double
mutant confirming a complex role for ethylene in the gravitropic response.
Abnormal floral organ development was observed in a subset of double
mutant flowers.These data demonstrate multiple connections between
auxin and ethylene during development and provide further insight into their
cellular interactions. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32601 |
| Date | 29 June 2000 |
| Creators | Madlung, Andreas |
| Contributors | Lomax, Terri L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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