Alleviation of Injury to Young Wheat Plants in Anaerobic Solution Cultures in Relation to the Supply of Nitrate and other Inorganic Nutrients

Abstract

We have investigated how far the supply of nitrate and other inorganic nutrients can alleviate the effects of anaerobic (anoxic) conditions around the roots of 13 d old wheat plants in solution culture. Anaerobic treatments of 2 weeks duration to the total root system caused inhibition of growth of roots and shoots, interference in ion accumulation by shoots, and premature leaf senescence. These responses, and the recovery of plants upon reoxygenation of their roots, could be modified greatly depending on the concentration of nitrate and other ions in the nutrient solution supplied either during or before the anaerobic treatment. Improvements in shoot growth and lessening of leaf senescence depended more on the shoot nutrient status than on the nitrate concentration in the nutrient solution during the anaerobic treatment. The growth of roots in the anaerobic solution was unaffected by changes in its ionic composition. A total alleviation of shoot injury was achieved by maintaining a single seminal root in aerated solution containing the full complement of inorganic nutrients. This effect was reversed by omitting nitrate from the aerated solution. We suggest that although nitrate is unlikely to act as an alternative electron acceptor to molecular oxygen when the latter is deficient it can, together with other ions, enter the shoots and there act as a nitrogen source for metabolism. We discuss the possibility that ions cross the oxygen-deficient, injured roots by mass flow thereby accounting for the requirement for a large external concentration to maintain adequate supplies to the shoot.