Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2001
Publication Date: N/A
Interpretive Summary: Slough grass (Beckmannia syzigachne Steud.), a summer annual, and tufted hairgrass (Deschampsia caespitosa L.), a perennial, are two native wetland grasses adapted to the moderate climate of the U.S. Pacific Northwest (PNW). Interest in their conservation has raised the question of their ability to re-seed and persist in the presence of non-native competitors. Tall fescue (Festuca arundinaceae Schreb.), a widely adapted species, is among several introduced grasses that are common in PNW wetlands. Decisions for best management practices in natural stands and rehabilitated sites may be influenced by better understanding the temperature adaptive mechanisms that influence plant performance, including identification of temperature optima. We used a previously published biochemical method to attempt to define the growth temperature optima for slough grass, tufted hairgrass, and tall fescue. Our attempt to reproduce the prescribed biochemical analysis for these species failed and therefore we were unable to define their temperature optima. We attributed our dissimilar findings to errors in the previously published protocol and thus have reported corrective measures to avoid future erroneous analyses.
Technical Abstract: The thermal dependence of enzyme kinetic parameters has been presented as an indicator of species thermal optima and tolerance limits. Previous studies suggest the relationship between temperature and the apparent Michaelis-Menten constant (Km) of an enzyme system can be used to predict whole plant success at specific temperatures. The apparent Km for glutathione reductase (EC 126.96.36.199, GR) (oxidized glutathione as substrate) extracted from leaves of slough grass (Beckmannia syzigachne Steud.), tufted hairgrass (Deschampsia caespitosa L.), tall fescue (Festuca arundinaceae Schreb.), and maize (Zea mays L.) was determined over a range of temperatures (1-40degC). For all species, minimum apparent Km for GR was observed at 1degC, and Km values increased as temperature increased. The apparent Km values differed among all species at the lower temperatures (1-15degC), but were similar at higher temperatures. The enzyme from tufted hairgrass had the lowest apparent Km at low temperatures (less than 15degC), followed in increasing order by slough grass, tall fescue, and maize. Our experimental system failed to reproduce "thermal kinetic window" profiles similar to those reported by others when cuvette condensation was eliminated from the spectrophotometer reaction chamber by the introduction of desiccated air. Cuvette condensation increased experimental error and skewed Km values at low temperatures. Results with these enzyme systems suggest that these cool-season species can be ranked as more to less eurythermic within the temperature range from 1 to 15degC.