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Titre : Glutathione S-transferase activity and glutathione levels in drought stressed Pinus brutia Ten. trees growing in Ankara

Auteur : Yılmaz, Can.

Université de soutenance : Middle East Technical University

Grade : Master of Science (MS) 2006

Résumé
Turkish red pine is coastal tree and is a drought resistant pine that withstands more aridity and poor soils than most other timber species growing in the same climatic conditions. In Turkey, this species grows in southern and western Anatolia and is also found in the Marmara region. Drought results in a water deficit in plant tissues, which, in turn, can lead to an imbalance in the redox poise of plant cells, and thus inducing oxidative stress in plants. Resistance to conditions associated with oxidative-stress must, in part, rely on endogenous antioxidative defense mechanisms required to maintain cellular homeostasis. Glutathione is one of the major endogenous antioxidants in plants known to play an important role in plant defense mechanisms. Glutathione S-transferase (GST, EC 2.5.1.18) is a GSH dependent detoxifying enzyme in plants, which catalyzes the conjugation of GSH. In this study, we investigated the changes in cytosolic glutathione S-transferase enzyme activity using CDNB as substrate and total thiol amount in Pinus brutia Ten., related to the drought stress during four months, June to September. The osmotic pressure in the needles was also determined as an indirect measure of drought condition. Together with the increase in the temperature values from June to July, GST enzyme activity increased from 15,78 ± 1,36 moles min-1 mg protein-1 to 22,91 ± 1,99 moles min-1 mg protein-1 which was statistically significant. However in August, GST activity had fallen to 16,54 ± 1,61 moles/min/mg protein, which may be because of a local rainfall at the beginning of the August in the sampling area. In September, GST activity significantly increased with respect to June, in accordance with high temperatures. The total thiol amount was not changed significantly during the sampling period. Although there were statistically significant changes in osmotic pressure in the needdles collected during the same sampling period, it did not exactly correlated to the changes in GST activity.

Mots clés : Pinus brutia, drought stress, glutathione S-transferase, glutathione, total thiol..

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