Poster: Integrated Plant Biology

Abs # 90: Characterization of the nitrate assimilation location in the model legume Lotus japonicus.

Presenter:	Gotbeter, Marilyn , nyliram7@yahoo.com
Authors	Gotbeter, Marilyn  (A)   Tapia, Susana  (B)   Ortega, Jose L (C)   Sengupta-Gopalan, Champa  (C)
Affiliations:	(A): MARC Program. New Mexico State University. (B): RISE Program. New Mexico State University. (C): Department of Agronomy and Horticulture. New Mexico State University.

Plants can acquire nitrogen in the form of nitrate and it is reduced to ammonia by the activity of two enzymes: Nitrate reductase (NR) and Nitrite reductase (NiR). Ammonia is then assimilated into glutamine by the activity of Glutamine synthetase (GS). Plants display two different isoforms of GS which differ in their subcellular locazlization. GS can be located either in the cytosol (GS₁) or in the chloroplast (GS₂). The current model on nitrate assimilation in legumes show that this process takes place in green tissues in association with the photosynthetic activity, which provides energy and carbon skeletons. In Lotus japonicus, a genetic model system for a legume, the location of nitrate assimilation activity has not been clearly demonstrated. It has been reported in the literature that L. japonicus plants lack the activity of NR in the leaves, suggesting that the roots may be the primary site of nitrate reduction and ammonia assimilation. This would imply an immense flow of carbon from the leaves to the roots to supply energy for reduction and C skeletons for assimilation. Preliminary experiments in our lab show an increase in the levels of GS₂ protein in the leaves of nitrate fed L. japonicus plants, supporting the current model on nitrate assimilation in the green tissues. To determine the exact location of nitrate assimilation in L. japonicus we will analyze the expression of genes for nitrate transport, nitrate reduction and nitrogen assimilation in Lotus plants treated with nitrate. We have used oligonucleotide primers to clone the genes for nitrate transporters, NR and NiR from Lotus by RT-PCR amplification. Through the study of the expression of these genes we will determine the exact sit of nitrate assimilation in Lotus japonicus.