Abstract
A more thorough understanding of the biochemical basis of superior performance of one alfalfa (Medicago sativa L.) genotype compared to another would expedite improvement in agronomically useful genotypes. Information on thermal dependence of glutathione reductase (GR, E.C. 1.6.4.2) in different ploidy levels of alfalfa is lacking. Our objective was to investigate the thermal dependency of GR in two genetically comparable populations of alfalfa at diploid and tetraploid levels. Thermal stability was similar for the enzyme from both populations, whereas variation was found for: i) the minimum apparent Km (0.53 and 4.14 μM NADPH), ii) the temperature at which the minimum apparent Km was observed (15 and 25° C), and iii) the thermal kinetic windows (TKW) (the temperature range over which the apparent Km is within 200% of the observed minimum Km, 5 and 20° C width) in diploid and tetraploid alfalfa, respectively. The TKW data suggest that the diploid can perform optimally under a narrower (i.e. smaller TKW) and lower range (i.e. the temperature at which the lowest Km was observed) of temperatures, whereas the tetraploid can perform optimally under a wider range (i.e. larger TKW) of temperatures. This finding is in agreement with previously published growth data on near-isogenic populations of diploid and tetraploid alfalfa.
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