|El Nashaar, Hossien|
Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2006
Publication Date: 9/30/2006
Citation: Banowetz, G.M., Azevedo, M.D., El Nashaar, H., Martin, R.C., Stout, R. 2006. Temperature-induced increase in cellular chelation potential associated with reduced thermotolerance. Journal of Thermal Biology. 32:12-19
Interpretive Summary: The yield and survival of wheat and other cool season grasses are severely impacted by hot summer temperatures. In contrast, panic grass, a grass that colonizes geothermally-heated soils adjacent to geysers, tolerates extended periods of exposure to temperatures that would be lethal to cool season grasses. Knowledge of the physiological adaptations that enable panic grass to survive at temperatures that would be lethal to wheat will be helpful in improving heat tolerance of wheat and other cool season grain and seed crops. Improving heat tolerance of these crops will reduce weather-associated cropping risks. We found that wheat, and a temperature-sensitive isolate of panic grass accumulate large quantities of substances that sequester cations, some of which are critical to the function of anti-oxidative enzymes that protect plants from many stresses, including heat. In contrast, heat tolerant isolates of panic grass accumulate less than half the amount of these substances during heat shock. Our study showed that these substances are low molecular weight compounds that appear to be charged. These characteristics will help in subsequent purification and characterization of the substances. Ultimately, knowledge of how to control their accumulation will enable development of new approaches to improve crop heat tolerance.
Technical Abstract: Panic grass, Dichanthelium lanuginosum var sericeum (Schmoll), successfully colonizes geothermally-heated soils that are subject to chronic temperatures ranging from 40 – 50 °C, occurs at altitudes in excess of 2500 meters and tolerates low soil moisture content for extended periods of time. In contrast to most grasses, D. lanuginosum shows high tolerance to the temperature stress, UV irradiation and dehydration associated with these environmental conditions. We utilized superoxide dismutase (SOD; EC 18.104.22.168) as an indicator of oxidative stress response to compare the impacts of temperature on wheat (Triticum aestivum L.), a cool-season grass, with that of three isolates of D. lanuginosum. One of the D. lanuginosum isolates was collected from a non-thermal site and had reduced capacity to adapt to growth at elevated temperature. The apparent stability of SOD in crude leaf extracts differed between wheat and a highly thermotolerant isolate of D. lanuginosum. Wheat SOD activity was significantly reduced by incubation at 45 °C while that from D. lanuginosum increased at 45 °C. One response associated with reduced thermotolerance was a heat shock-associated increase in cellular chelation capacity. Greatest Increases in chelation potential were measured in wheat and the D. lanuginosum isolate with the least thermotolerance. Apparent SOD activity was reduced with increased chelation potential because ultrafiltration of leaf extracts through 10 kD membranes, which removed much of the chelating activity, restored apparent SOD activity. Whole plant SOD responses to heat shock were not correlated with relative heat tolerance. The D. lanuginosum isolate that displayed the greatest tolerance retained SOD activity while leaf SOD activity was significantly reduced in the isolate showing the least tolerance. In contrast, wheat SOD activity increased in response to heat shock. The temperature-associated increase in chelation capacity, greatest in wheat and the D. lanuginosum isolated from a non-thermal site, was associated with low molecular components (<10 Kd) that did not bind C18 media.