Factors Affecting Seed Protein Concentration in Oats I. Metabolism and Distribution of N and Carbohydrate in Two Cultivars that Differ in Groat Protein Concentration 1

Cultivars of Avena sativa L. that have high (cv. ‘Dal’) or low (cv. ‘Orbit’) groat protein concentration were evaluated for their ability to enzymatically reduce nitrate and to store and remobilize nitrogenous compounds and nonstructural carbohydrates. Nitrate reductase (E.C. 1.6.6.1) activity/plant (i.e., potential for reducing nitrate) was similar for the two cultivars grown in the field or environmental chambers, and exceeded the level needed to account for the actual accumulation of reduced N in the whole plant. The contribution of various plant parts to total reduced N varied ontogenetically. Leaf sheaths, roots, and bracts, as well as leaf blades, had significant levels of nitrate reductase at specific times in development. Accumulation of total reduced N by the groats was comparable in the two cultivars, but the contribution from remobilized N differed. On a whole‐plant basis, Dal continued to accumulate N until maturity, whereas Orbit ceased accumulation just after anthesis. Although the yield of groats per primary shoot was 14% lower in Dal as compared to Orbit, the accumulation of total nonstructural carbohydrates in groats of Dal was 25% lower than in Orbit. Total deposition of nonstructural carbohydrates in vegetative tissues was 75% higher in Orbit than in Dal. Losses of total nonstructural carbohydrates (respiration and remobilization to groats) from vegetative tissues of Orbit during groat development exceeded losses from Dal by 124%. Since respiration rates were comparable, Orbit apparently remobilized much more stored carbohydrates to developing groats than did Dal. Differences in C metabolism of these cultivars may be more important than differences in N metabolism in influencing groat protein concentration.