The Dominant Influence of Nitrogen on Growth Correlation in Etiolated Oat Seedlings

Abstract

A nutritive hypothesis is put forward to account for the inhibitory effect of carbon dioxide, and of sucrose, on the elongation of the coleoptile and leaves of etiolated oat seedlings. Growth depends, it is assumed, on the availability of nitrogen, and the way in which the supply is diminished by these treatments has been elucidated. Three factorially arranged experiments were carried out to provide the necessary growth data and observations were also made of the distribution throughout the seedlings of dry-weight, of sugars and of nitrogen. Additionally, the quantity of reserves, and of nitrogen, flowing into the seedling during growth have been determined. The dependence of coleoptile and leaf growth on the supply of nitrogen has been demonstrated and also the dependence of the amount of nitrogen transferred on the total weight of translocate. The growth inhibition can then be explained on the assumption that treatment with carbon dioxide and sucrose decreases the weight of reserves translocated from the endosperm and so reduces the amount of nitrogen passing into the seedling. Consumption of nitrogen by the mesocotyl and roots, however, is not correspondingly reduced; the coleoptiles and leaves, perforce, bear the entire shortage and their growth is checked. These results may also be utilized to explain the transient growth promotion of the coleoptile and leaves brought about by illumination and heating, so avoiding the need to postulate changes in auxin metabolism. The importance of the nitrogen supply during germination is discussed.