Date of Award
5-17-2012
Document Type
Thesis
Degree Name
Chemistry, MS
First Advisor
Argelia Lorence
Committee Members
Allyn Ontko; Fiona Goggin
Call Number
LD251 .A566t 2012 K32
Abstract
Vitamin C (ascorbate, AsA) is the most abundant water soluble antioxidant in plants and is essential for plant and human health. Ascorbate plays a key role in protecting plants from reactive oxygen species generated during normal metabolic processes and under stress conditions including wounding, pathogen attack, salt, heat, light, and ozone exposure. Jasmonates (JAs), a group of plants hormones involved in stress responses also protect plants from these stresses. There is evidence indicating that JAs modulate AsA content in plants. The recent discovery of the inositol pathway has opened possibilities for AsA enhancement via metabolic engineering in plants. Over-expression of enzymes from this pathway including myo-inositol oxygenase (MIOX) and glucuronate reductase (GlcUR) has resulted in 2 to 4-fold higher AsA levels in Arabidopsis. The aims of this study were twofold: 1) Test if over-expression of the Arabidopsis MIOX4 and GlcUR genes leads to enhanced AsA content in tomato, and 2) gain a deeper understanding about the role of JAs in modulating AsA content in Arabidopsis. Cotyledons of tomato var. Castlemart and MicroTom were transformed with a AtMIOX4:pBIB-Kan and a AtGlcUR:pBIB-Kan construct. Presence of the transgenes in the primary transformants (T0) was confirmed via PCR. Unfortunately none of the progeny (T1) contained AtMIOX4 and AtGlcUR. We concluded that the T0 lines we generated were most likely chimeras. Next, we decided to test our hypothesis on a transient expression system in tomato fruits. Tomato var. MicroTom fruits transiently expressing AtMIOX4 showed 3-fold higher AsA levels compared to controls injected with the empty vector. To gain a deeper understanding about the role of JAs in modulating AsA content, we first established the baseline AsA foliar content of Arabidopsis JA mutants and compared those to wild type (WT) controls. Our results indicate that the acx1/5 mutant has significantly lower AsA content than WT. Interestingly by measuring AsA content after wounding in WT vs. acx1/5 we learned that acx1/5 is still able to respond to this insult, despite its inability to synthesize JAs. This data indicates that there are signals other than JAs mediating this response. We also inspected microarray gene expression data deposited at Genevestigator and noticed a significant overlap between genes involved in AsA biosynthesis that are regulated by JAs and genes in this network that are regulated by AMR1, a negative master regulator of genes in the mannose/galactose route to AsA. Exogenous treatment of MeJA to AMR1 knockouts showed a significant increase in AsA level indicating that in absence of AMR1, expression of these genes is further enhanced by JAs.
Rights Management
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Kulkarni, Shashank S., "Elevating Ascorbate Content in Tomato and Studying the Role of Jasmonates in Modulating Ascorbate in Arabidopsis" (2012). Student Theses and Dissertations. 869.
https://arch.astate.edu/all-etd/869
