Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2005
Publication Date: 4/12/2005
Citation: Light, G.G., Roxas, V.P., Mahan, J.R., Allen, R.D. 2005. Transgenic cotton (Gossypium hirsutum L.) seedlings that express a tobacco glutathione S-transferase fail to provide improved stress tolerance. Planta. 222(2):346-354. Interpretive Summary: Low temperatures at and following planting often reduce seedling growth. These early-season growth reductions ultimately reduce yield at the end of the season and result in decreased profits for producers. Harmful chemicals called oxidants are produced by plants under stress and are responsible for some low temperature damage. Plants have mechanisms that protect them against low temperature oxidants but they are not capable of completely preventing damage. In this study one of the protective mechanisms, the enzyme glutathione S-transferase (GST), was artificially enhanced by inserting a gene from tobacco. While the enzyme was found to be present at higher levels, there was no positive effect on the ability of the plants to withstand stress. Changes were noted in other aspects of antioxidant metabolism though there was no overall positive effect on the plants. These results show that expression of a tobacco GST in cotton does not provide adequate protection against oxidative and suggests that the endogenous antioxidant system in cotton may be disrupted by the expression of the tobacco GST. These findings suggest that alterations of antioxidant metabolism by transgenic techniques may not be a universally successful approach to the development of plants with low temperature stress tolerance.
Technical Abstract: Transgenic cotton (Gossypium hirsutum L.) lines expressing the tobacco glutahione S-transferase (GST) Nt107 were evaluated for tolerance to chilling, salinity, and herbicides, antioxidant enzyme activity, antioxidant compound levels, and lipid peroxidation. Although transgenic seedlings exhibited 10-fold and 5-fold higher GST activity under normal and salt-stress conditions, respectively, germinating seedldings did not show improved tolerance to salinity, chilling conditions, or herbicides. Glutathione peroxidase (GPX) activity in transgenic seedlings was 30 to 60% higher under normal conditions, but was not different than GPS activity in wild-type seedlings under salt-stress conditions. Glutathione reductase (GR), superoxide dismutase (SOD), ascorbate peroxidase (APX), and monodehydroascorbate reductase (MDHAR) activities were not increased in transgenic seedlings under salt-stress conditions, while dehydroascorbate reductase (DHAR)activity was decreased in transgenic seedlings under salt-stress conditons. Transgenic seedlings had 50% more oxidized glutathione when exposed to salt stress. Ascorbate levels were not increased in transgenic seedlings under salt-stress conditions. Malondialdehyde (MDA) content in transgenic seedlings was nearly double that of wild-type seedlings under normal conditions and did not increase under salt-stress conditions. These results show that expression of Nt107 in cotton does not provide adequate protection against oxidative and suggests that the endogenous antioxidant system in cotton may be disrupted by the expression of the tobacco GST.