Seasonal fluctuations of nitrate reductase activity in ditelosomic stocks of wheat

In vivo nitrate reductase activity was measured over the season in individual organs of the main tiller of the euploid and four ditelosomics of the wheat variety Chinese Spring. A general biphasic profile of leaf activity was obtained in vivo and in vitro, the peaks corresponding to emergence of leaf 7 (the pre-flag leaf) and the ear. A wide range of seedling nitrate reductase activity was exhibited by these stocks and a significant positive correlation was obtained between seedling activity and the daily mean of activity integrated over the season. Seasonal euploid-ditelosomic differences in nitrate reductase activity reflected differences over the vegetative stage, but no significant inter-stock differences in activity were found over the reproductive stage. The high seasonal nitrate reductase activity of ditelo-7B^L and -7B^S appeared to be due largely to high mean activities of individual leaves, while that of ditelo-4B^L depended on the longer duration of active tissue than was exhibited by the euploid. Significant activity was assayed in non-leaf organs, especially the rachis and awns, and constituted an important proportion of the total tiller activity late in the season.