Date of Award

Winter 1994

Project Type

Dissertation

Program or Major

Plant Biology

Degree Name

Doctor of Philosophy

First Advisor

Brent Loy

Abstract

Asparagus officinalis L. is typically classified as a dioecious species. However, in all-male hybrid cultivars, a percentage of individuals within a population exhibit a persistent perfect flowering (hermaphrodite) phenotype. Floral meristem development was divided into eight distinct stages of development and those developmental stages were compared in UC157 male, UC157 female, and 32/83 hermaphrodite individuals using scanning electron microscopy (SEM). In females, anthers abort between stages five and six. In males, style development is halted at stage eight. Hermaphrodites exhibit normal development of both anthers and styles. Within the 32/83 cultivar, the number of developing carpels can vary and some unusual pistil types are observed. The timing of floral organ development is delayed in females compared to males and hermaphrodites. However, once a meristem becomes committed to flowering, the development of complete floral organs occurs in approximately three days. An additional four to seven days is required before anthesis occurs or pistils become receptive to pollen. Protein profiles of three day post-emergent spears show distinct qualitative and quantitative differences between sex types. Distinctly different proteins are expressed in vegetative cladophyll tissue and floral bud tissues as well.

Floral homeotic genes in other plant species contain a DNA binding domain (MADS box) common to a family of transcription factors. MADS boxes were cloned from male asparagus via PCR technology. Eight unique asparagus MADS box clones group into three distinct classes based on distance matrix analysis. UPGMA analysis of amino acid sequences shows five of the asparagus clones clustering independently from other known plant MADS domains which suggests they may represent a new class of MADS domain. The remaining three asparagus clones cluster with the Arabidopsis Agamous MADS domain. Computer modeling indicates the new class of MADS domain has some similarity in secondary protein structure with the Agamous MADS domain from Arabidopsis.

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