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Lariviere, Andrew (2015) LEAF SALICYLIC ACID CONCENTRATION AND INSECT HERBIVORY. Master's Thesis, University of Pittsburgh. (Unpublished)

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Due to their stationary existence, plants are exposed to an array of attackers including pathogens and insect herbivores. In defense, plants employ sophisticated responses mediated by the hormones salicylic acid (SA) and jasmonic acid (JA). These two hormones act antagonistically to fine-tune expression of defense compounds to a particular attacker. This is an important component of optimal defense theory (ODT), which states that expression of defenses is costly due to limited metabolic resources. Several studies have shown that increased expression, or exogenous application, of SA inhibits expression of JA-mediated defenses, and vice versa. However, no studies have investigated how constitutive SA levels affect JA-mediated defenses. After reviewing the literature on ODT, I present a review of the mustard family (Brassicaceae) and their specialist insect herbivores Pieris butterflies, which is the model system used in my first study. In this study, I compared constitutive SA levels in five spring-flowering and five summer-flowering mustard species and found that the spring-flowering species received significantly less herbivory and supported lower caterpillar relative growth rate (RGR) than the summer-flowering species. I then asked whether the differences that I observed could be explained by the underlying leaf SA concentrations. I found that the species with the lowest constitutive SA concentrations were the most resistant to herbivory and supported the lowest larval RGR. The highest herbivory rate and RGR occurred in species with intermediate concentrations of constitutive SA. In a second study, I investigated the inhibition of JA-mediated defenses by induced SA levels. I applied a commonly-used SA analog to five mustard species then measured RGR of the generalist caterpillar, Trichoplusia ni. I found that exogenous SA increased plant susceptibility in most, but not all plants. The exception being an agricultural variety of the perennial plant, Lesquerella fendleri.
I conclude that low constitutive SA concentrations may benefit plants by reducing herbivory and larval growth rates of insect herbivores. The finding that constitutive SA levels affect herbivore performance is unprecedented and has implications for our understanding of the evolution of plant defenses and for the cultivation of more insect-resistant crops.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Lariviere, Andrewahl15@pitt.eduAHL15
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairCarson, Walterwalt@pitt.eduWALT
Committee MemberTraw, M
Committee MemberMorehouse, Nathannim@pitt.eduNIM
Committee MemberRebeiz, Markrebeiz@pitt.eduREBEIZ
Date: 9 January 2015
Date Type: Publication
Defense Date: 19 November 2014
Approval Date: 9 January 2015
Submission Date: 26 November 2014
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 92
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Salicylic acid, jasmonic acid, Brassicaceae, Pieris rapae, plant defense, crosstalk
Date Deposited: 09 Jan 2015 18:18
Last Modified: 15 Nov 2016 14:25


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