Nitrate reduction in the roots and shoots of wheat seedlings.

Intact wheat seedlings cultured in high nitrate solutions (high-NO 3 (-) cultures) reduced NO 3 (-) when placed for 24 hr in dilute CaSO4 solutions although they leaked NO 3 (-) back to solution during this period. Most of the reduction seemed to occur in shoots since in parallel experiments detached shoots reduced nearly as much of the previously absorbed NO 3 (-) as intact cultures. Detached roots leaked greater quantities of NO 3 (-) back to solution than did intact cultures, and failed to reduce any of their previously absorbed NO 3 (-) during the experimental period. Seedlings of identical age cultured without a nitrogen source and rich in carbohydrate reserves (low-N cultures) rapidly absorbed NO 3 (-) from dilute Ca(NO3)2 solutions and reduced 80% of that absorbed. Detached low-N roots also absorbed NO 3 (-) and reduced 40% of that absorbed. Total NO 3 (-) reduction by intact low-N cultures over the 24-hr period was comparable to that of high-NO 3 (-) cultures in spite of the fact that in vitro nitrate reductase activity of the former did not reach the levels found initially or at the end of the period in the latter, and that the total NO 3 (-) absorbed by low-N cultures was less than that initially present in high-NO 3 (-) cultures.