Reversal of Nitrate Inhibition of Nodulation by Indolyl-3-acetic Acid

Abstract

NITRATE appears to have an influence on the action of indolyl-3-acetic acid (IAA) in the initiation and development of the symbiosis between legumes and bacteria of the genus Rhizobium. For example, it is often suggested that IAA is responsible for the curling of root hairs that is taken to be a prelude to the bacterial invasion of the legume root¹, and Thornton² noted that the percentage of lucerne root hairs that were deformed in the presence of Rhizobium meliloti culture filtrates was reduced if the plants were simultaneously supplied with NaNO₃. IAA is likewise proposed to be involved in the nodulation process itself³, the nodule biogenesis likewise being repressed by nitrate. Recently, Tanner and Anderson⁴ suggested that the inhibition may be attributable to a destruction of auxin by the nitrite produced from the bacterial reduction of nitrate. In this communication, it is demonstrated that not only may nitrate influence the lAA-induced changes but also that IAA may, conversely, mitigate the inhibition of nodulation by nitrate.