Flushing of nitrogen gas through culture solutions, for periods between 4 and 15 h, increased activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) in roots of intact maize plants (activities expressed as μmol mg protein−1 min−1). The activity of ADH was six to nine times greater than the activity of PDC.
Under root anaerobiosis of intact maize plants, activities of both ADH and PDC were similar in all root segments taken between o and 37 mm behind the apex, but lower activities were found in the older root segments. These differences in enzyme levels between younger and older root tissues were affected neither by the light regime of the shoots nor by imposing anaerobiosis of the shoots as well as the roots; i.e. the differences in ADH and PDC activities found in root segments of different ages were not due to a superior oxygen supply from the shoots to the tissues near the shoot-root junction.
Roots of intact maize plants were also exposed to a range of oxygen concentrations, by flushing the nutrient solution with gases of different composition. ADH activities in the roots were highest with gas mixtures containing 8–13% oxygen, intermediate with pure nitrogen, and lowest when the solution was flushed with gas containing 20% oxygen.
It is concluded that ADH activity cannot be used to diagnose the degree of oxygen deficiency to which maize roots have been exposed.
N, N-bis (2-hydroxyethyl) glycine
2-(N-morpholino) ethane sulphonic acid