Date of Graduation

5-2016

Document Type

Thesis

Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor

Kenneth L. Korth

Committee Member

Douglas Rhoads

Second Committee Member

Vibha Srivastava

Keywords

Biological sciences; Gene expression; Microarray; Nighttime temperatures; Temperature stress

Abstract

Starch composition and grain quality of rice is greatly influenced by genotype and environmental factors. The detrimental effects of high nighttime temperatures on rice yield and quality has recently become apparent, with some of the warmest average nighttime temperatures being recorded in the past few years. One of the most notable effects of this stress, an increase in grain chalk formation, correlates with a decrease in quality. This effect varies greatly between cultivars as some show less temperature-sensitive quality reduction than others. The goal of this research is to elucidate fundamental changes that occur in developing plants and grains as they respond to high nighttime temperatures. Two cultivars were used: Cypress, considered to have greater tolerance to high temperatures, and LaGrue, considered more susceptible. To assess physiological differences between cultivars, gas exchange measurements were collected from field-grown plants to determine photosynthetic rates. Gene expression analysis was carried out using DNA gene strip arrays using endosperm tissue isolated from plants grown in temperature-controlled conditions, identified genes differentially expressed in these cultivars. Differential gene expression was seen between cultivars regardless of nighttime temperature. There were however, few genes showing differential expression in response to temperature treatment within a cultivar. Among the genes differentially expressed between cultivars, no differences were observed in genes encoding enzymes in the starch biosynthesis pathway. Furthermore, no significant differences were found among genes encoding enzymes involved in amyloplast packaging or starch breakdown. Cypress endosperm had higher levels of expression in many genes involved in cell wall organization. LaGrue had a significantly higher photosynthetic rate during grain filling stages of development. The increased rate of photosynthesis may be related to the larger panicle on LaGrue leading to a stronger sink demand for carbon. This work adds to understanding the combined effects that genotype and environment have on rice quality. There were few differences observed in endosperm gene expression but a difference was seen in physiological measurements, therefore future research can focus on what influence these physiological differences play in rice quality.

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