A traditional view of plant nutrition holds that microbes have to convert organic sources of nitrogen into inorganic forms before the nitrogen can be used by plants.
More recently, however, it has been suggested that crop plants may be able to take up organic nitrogen directly.
In the experiments reported here, nitrogen-free solutions were prepared and then sterilised by autoclaving. Either sodium nitrate or ammonium chloride was added to produce 3 mM solutions and solutions containing 1.5, 3 or 6 mM glycine (an organic compound) were also prepared. Control solutions contained no nitrogen. Tomato seeds were surface sterilised and placed in sterile flasks to germinate. The seedlings were then transplanted into flasks containing the test solutions, which were changed every three days. Any flasks showing signs of microbial contamination were discarded. After 21 days, the seedlings were removed and weighed. Seedling weight increased with increasing concentration of glycine and the weight in 3 mM glycine was similar to that obtained with 3 mM sodium nitrate.
The results clearly demonstrated that tomato seedlings were able to use an organic nitrogen source directly and they suggest that simple organic sources of nitrogen may have potential as nitrogen sources for tomato crops.
Influence of Inorganic and Organic Nitrogen on Enzymes of Nitrogen Assimilation and Growth in Tomato Seedlings by Ge, Roberts, Jones, Yang, Song, Lu-Bo, Ming-Ding and Huang (2008). Journal of Horticultural Science & Biotechnology 83 (4): 513-519. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com.