The Effects of Heat Stress on Reactive Oxygen Species Production and Chlorophyll Concentration in Arabidopsis Thaliana

Abstract

Environmental and ecological changes due to temperature increase, such as those associated with global climate change, have been well documented. Since temperature fluctuations are greater on a regional rather than global scale, research quantifying plant responses to heat stress has become a principal objective for environmental and ecological biologists. Aerobic organisms generate reactive oxygen species (ROS) in healthy cells at a controlled rate, however, at elevated temperatures, oxidative stress can create an imbalance between the production of ROS and the ability to detoxify and remove the reactive intermediates. ROS concentration was compared between heat-stressed and optimally grown Arabidopsis thaliana, ecotype Col-0. The control group was grown at 23°C/23°C day/night for a 12 hour photoperiod while the heat stressed group was grown at 29°C/23°C day/night for a 12 hour photoperiod. All plants were grown on Murashige and Skoog (M&S) Basal Salt agar plates enriched with 1N KOH. Measuring the concentration of Thiobarbituric Acid Reactive Substances (TBARS) such as malondialdehyde (MDA), a common ROS, is a well-established method for detecting and quantifying oxidative stress. Results using a colorimetric assay demonstrated that heat stressed plants had a 68.30% higher concentration of TBARS than optimally grown plants (P = 0.0005). And, since TBARS production is associated with lipid peroxidation and membrane integrity, it stands to reason that photosynthesis may also be affected. In order to measure chlorophyll concentration, chloroplasts were isolated and purified. Results of colorimetric assays indicated that chlorophyll was reduced by 41.4% in heat stressed plants P = 0.0005. Thus, heat stress results in an increase in oxidative stress, lipid peroxidation, a higher than optimal concentration of ROS in the plant tissue and may further impair the plant’s ability to photosynthesize by reducing chlorophyll content.