Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/1999
Publication Date: N/A
Interpretive Summary: During periods of water stress plants produce harmful chemicals that can negatively affect their subsequent growth and development. Some of these chemicals, oxidants, can damage cells through a process called oxidation. Plants have a variety of mechanisms that help reduce damage caused by oxidation and thus improve the plant's ability to thrive in unfavorable environments. It has been previously proposed that these "antioxidant sys- tems" of plants are not always effective and as a consequence plants are frequently damaged by oxidants. Efforts to analyze limitations in anti- oxidant systems have not clearly defined the limitations in antioxidant systems under agricultural conditions. In order to determine the best approaches to enhancing antioxidant metabolism in plants grown under agri- cultural conditions it is necessary to know when and to what extent anti- oxidant systems may be limiting. In this study we have monitored the status sof one portion of the antioxidant system, glutathione, in an effort to observe and define limitations. Cotton was grown under two levels of irri- gation: a rainfed that received a preplant irrigation and an irrigated treatment that received periodic irrigations. Leaves were sampled from both treatments at various times during the growing season and the amount and chemical form we determined. It was expected that changes in both the amount and chemical form of glutathione in the leaves would be observed in response to water stress. While the total amount of glutathione varied over the season in both treatments, there were no differences between the treat- ments in the amount of glutathione present in the leaves. Both the irri- gated and rainfed tissues had the same amount of glutathione at each point during the season.
Technical Abstract: Cotton (Gossypium hirsutum L.) that is grown in semi-arid regions is frequently subjected to oxidative stresses due to sporadic rainfall and deficit irrigation. Glutathione is an antioxidant present in cotton and other plants that is involved in the detoxification of harmful active oxygen species. Recent advances in molecular biology have demonstrated the feasibility of altering various aspects of glutathione metabolism and it has been proposed that such alterations will improve the performance of plants experiencing oxidative stress. The efficacy of such metabolic alterations will depend on to what extent they alleviate pertinent limitations in glutathione metabolism. Currently there is no information that defines the pattern and extent of variation in the glutathione content of cotton leaves under stressed and nonstressed conditions. Such information will be of value in future efforts to improve antioxidant metabolism in cotton under water stress. In this study glutathione content and form (oxidized or reduced) in the leaves of field-grown cotton were measured over a growing season under two irrigation levels. While the glutathione pool varied more than 2.5 fold over the sampling interval there was no effect of water treatment on the variation. Additionally, the pool of reduced glutathione did not vary in response to the water deficits. These results suggest that the form and amount of glutathione may not limit the response of cotton to oxidative stresses resulting from field-water deficits.