Temperature-induced increase in cellular chelating potential associated with reduced thermotolerance

Hot springs panic grass, Dichanthelium lanuginosum var sericeum (Schmoll), successfully colonizes geo-thermally heated soils that are subject to chronic temperatures ranging from 40 to 50 1C, occurs at altitudes in excess of 2500m, and tolerates low soil moisture content for extended periods of time. We utilized superoxide dismutase (SOD; EC 1.15.1.1) as an indicator of oxidative stress response to compare the impacts of temperature on wheat (Triticum aestivum L.), a cool-season grass, with the temperature responses 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. Wheat SOD activity in crude leaf extracts was significantly reduced by incubation at 45 1C. In contrast, SOD activity in crude leaf extracts from a thermophilic D. lanuginosum isolate increased after incubation at 45 1C. Significant increases in cellular chelating capacity occurred in wheat and the D. lanuginosum isolated from a non-thermal environment after plants were exposed to elevated temperatures. Ultra-filtration of leaf extracts through 10 kDa molecular weight cutoff membranes removed much of the chelating activity and restored apparent SOD activity. The D. lanuginosum isolates with the greatest thermotolerance retained SOD activity when exposed to elevated temperatures and did not show statistically significant increases in cellular chelation potential. Wheat SOD activity increased in response to heat shock. The chelation activity was associated with low molecular weight components (o10 kDa) that did not bind C18 media. Ultra-filtration removal of these low molecular weight chelating components increased SOD activity and replacement of low molecular weight chelating components with an equivalent amount of EDTA suppressed SOD activity. r 2006 Elsevier Ltd. All rights reserved.