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Universiti Putra (2013)

Functional characterization of alcohol dehydrogenase genes in Arabidopsis plants grown under drought condition

Myint, Thawda

Titre : Functional characterization of alcohol dehydrogenase genes in Arabidopsis plants grown under drought condition

Auteur : Myint, Thawda

Université de soutenance : Universiti Putra

Grade : Doctor of Philosophy (PhD) 2013

Résumé
In response to drought, plants change their metabolic activities towards limiting cellular water consumption and loss. One metabolic process that is affected by this stress is ethanolic fermentation. In plants, ethanolic fermentation occurs during limited oxygen condition and under certain environmental stresses. The effects of ethanol fermentation on plant growth and survival under drought stress are not well explained. In addition, previous studies on ethanolic fermentation in plants were limited to alcohol dehydrogense (EC.1.1.1.1) enzyme activity and gene expression. In this study, it was hypothesized that ethanolic fermentation is required to enhance plant ability to retain cellular water under drought. Enhancing the capacity of ethanolic fermentation in a plant would improve the plant ability to retain cellular water ; thus, retain the plant’s photosynthetic capacity. To test the hypothesis, this study was carried out with the following objectives : i) to identify the specific ADH genes responding to drought in Arabidopsis plants, ii) to evaluate the effects of defective ADH on growth and drought-related parameters, iii) to evaluate the effects of enhanced ethanolic fermentation on growth and drought-related parameters. The objectives were achieved by a combination of the gain-and the loss-of-function approaches. For the gain-of-function approach, an Arabidopsis plant over-expressing the ADH1 transgene was developed using the Gateway technology where fully characterized homozygous lines were used for the analysis. As for the loss-offunction approach, the T-DNA insertion mutant lines with impaired ADH genes were used. The plants were exposed to polyethylene glycol-induced drought stress, and their responses at physiological, biochemical and molecular levels were analysed together with their overall growth performance. In the present study, the level of relative water content (RWC) of Arabidopsis plants dropped to 75% from the initial level of 85% when treated with 5% (w/v) PEG-20,000, demonstrated that the plants were moderately water-stressed. The stressed plants had high levels of proline and low levels of chlorophyll. At enzyme and metabolite levels,both the root and leaf NADH-ADH activities were increased 5.9 and 4.4 folds,respectively. For pyruvate decarboxylase (PDC), the activity was increased in the root (1.2 folds) and in the leaf (4.4 folds). Ethanol, the end product of ethanol fermentation was accumulated in both the leaf (3 folds) and root (2 folds). The increase in the level of ethanol was parallel with the increase observed in the activities of NADH-ADH and PDC. At gene level, the majority of the ADH and PDC genes were up-regulated

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