Distribution of Nitrate and Nitrite Reductase in Barley

Abstract

BOLLARD¹ and Wallace and Pate² have shown that most of the nitrogen transported in the cell sap of both dicotyledons and monocotyledons is in the organic form. Their results imply that the majority of the incoming nitrogen is incorporated into organic compounds in the root. Presumably, because nitrate is considered to be reduced to ammonia before incorporation into amino-acids and other nitrogenous compounds, this reduction must also occur in the root. Most work on the enzymes involved in nitrate reduction in higher plants, however, has been done using leaf tissue. Sanderson and Cocking³ have found significant nitrate reductase activity in cell-free preparations of tomato, barley, wheat and potato roots, and other investigations with root extracts of a variety of species have either failed to demonstrate the presence of the enzyme⁴ or only shown it to be capable of very low rates of activity^4–7. It is unlikely that these latter results are due to the absence of the enzyme from root tissue, but rather to a failure to obtain the optimum conditions of extraction. To my knowledge the only report of nitrite reductase activity of a level comparable with that found in leaves has been by Sanderson and Cocking⁸, using extracts of tomato root.