• Login
    View Item 
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

    My Account

    LoginRegister

    About

    AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA CatalogsUA Libraries

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    The role of phytoecdysteroids in spinach (Spinacia oleracea): Physiological responses to below ground herbivory support a plant defense hypothesis

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    azu_td_9927458_sip1_c.pdf
    Size:
    6.311Mb
    Format:
    PDF
    Download
    Author
    Schmelz, Eric Alexander
    Issue Date
    1999
    Keywords
    Biology, Entomology.
    Chemistry, Analytical.
    Biology, Plant Physiology.
    Advisor
    Bowers, William S.
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Polyhydroxylated steroids with insect molting hormone activity were discovered in plants over thirty years ago. The major endogenous molting hormone of insects is believed to be 20-hydroxyecdysone (20E) and interestingly, it is also the most commonly encountered phytoecdysteroid (PE) in plants. Ecdysteroids control developmental programs in both immature and adult insects however, the role of PEs in plants has not been demonstrated. PEs are hypothesized to function as either plant hormones or plant defenses against phytophagous insects. Many toxic secondary metabolites are concentrated in apical meristems where herbivory would result in the greatest reduction in plant fitness. Similarly, the highest concentrations of 20E in spinach were associated with the stems and vasculature while old leaves and roots displayed low levels. In plants, concentrations of toxic or deterrent metabolites are often rapidly induced following attack. In spinach roots, both mechanical damage and insect herbivory resulted in rapid increases in 20E concentrations. The plant wound signal, jasmonic acid was strongly implicated in signaling this response. Known plant hormones and chemical defenses are regulated differently. Pulse chase studies with [2-¹⁴C] mevalonic acid demonstrated that de novo root 20E biosynthesis occurred during the induction and, once synthesized, 20E was stable for over one month. This result is does not support the plant hormone hypothesis, as plant hormones typically undergo rapid conjugation or catabolism. The induction of root 20E concentrations occurred without similar changes in related membrane phytosterols. Simply, pathway specificity was demonstrated as increased 20E accumulation was not part of an overall increase in steroids. To empirically examine the hypothesis that PEs function as plant defenses against insects, a series of experiments were designed with the fungus gnat Bradysia impatiens. Results indicated that root herbivory by larvae induced 20E levels in roots, larval preference for diets containing induced 20E levels was reduced, larval survivorship on 20E containing diets was lower, and plants with induced root 20E levels were better protected from attack. Together, these results support the plant defense hypothesis at both the physiological and ecological level.
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Entomology
    Degree Grantor
    University of Arizona
    Collections
    Dissertations

    entitlement

     
    The University of Arizona Libraries | 1510 E. University Blvd. | Tucson, AZ 85721-0055
    Tel 520-621-6442 | repository@u.library.arizona.edu
    DSpace software copyright © 2002-2017  DuraSpace
    Quick Guide | Contact Us | Send Feedback
    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.