Date of Award

2012

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Clore, Amy

Keywords

Brassinosteroid Signaling, Carpel Fusion

Area of Concentration

Biology

Abstract

Two carpels undergo fusion to form one gynoecium during female reproductive organ development in Catharanthus roseus L. Fusion in C. roseus is unique among organ fusions in that approximately 400 of the contacting cells change cell fate from epidermal to less specialized parenchyma during this process. Such a change in fate is known as dedifferentiation. Previous research has shown that an unknown diffusible 'factor' is exchanged between the carpels to induce fusion. Furthermore, this 'factor', collected from between the carpels and applied to other carpel epidermal cells outside of the fusing region, causes these recipient cells to change cell fate. Evidence is presented herein that brassinosteroid signaling plays a role in dedifferentiation of the 400 contacting cells. Buds treated with the brassinosteroid inhibitor, Brz2001, did not undergo complete fusion as determined by morphological and histological analyses. Gynoecia treated with brassinosteroid inhibitors during development were only superficially fused indicating that there may be two separate processes involved, namely, surface adhesion and deeper tissue fusion. Rescue experiments with brassinosteroid inhibitor and exogenous brassinosteroid hormone resulted in seemingly normal fusion. Wheat leaf unrolling bioassays demonstrated that carpel exudates stimulated unrolling in etiolated wheat leaves, comparable to the brassinosteroid, epibrassinolide and significantly greater than the controls. In contrast, the treatment of normally non-dedifferentiating carpel epidermal cells with a different (non-steroidal) hormone, benzylaminopurine, did not result in changes in cellular morphology. A PCR product of the predicted size was amplified from C. roseus DNA when degenerate primers were used in an attempt to amplify BRI1 (which encodes the brassinosteroid receptor) consistent with the notion that this pathway may be active in this process. Finally, cuticle permeability assays using cell wall-binding dyes were used to test the hypothesis that cuticle modification participates in carpel fusion. Results support this hypothesis, although further analyses are needed. This research contributes to insights into organ fusion, cell signaling, and change in cell fate, which have relevance in and outside of the field of plant reproductive development.

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