242:	Photosynthate partitioning in perennial grasses can influence the site of nitrate metabolism.

Authors:	Jiang, Zhongchun(A)Bushoven, John(A)Hull, Richard, J.(A)
Affiliations:	(A): University of Rhode Island
Presenter:	Hull, Richard J., rhu6441u@postoffice.uri.edu

The efficient use of nitrogen depends upon effective nitrate absorption, its subsequent reduction to ammonium and its assimilation into glutamate. We have shown that grasses which reduce and assimilate nitrate primarily in their roots also exhibit a larger root:shoot ratio. Three C-3 perennial grasses [Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.)] were compared for their root versus shoot nitrate metabolism when grown under conditions that altered the pattern and extent of their photosynthate partitioning. Grasses were grown in modified Hoagland's solution and nitrate reductase activity was monitored in leaves and roots by an in vivo method modified for these grasses. Conditions that stimulated photosynthate translocation to roots also promoted a greater percentage of total plant nitrate assimilation in roots. These results will be discussed in terms of energy availability determining the primary sites of nitrate reduction and assimilaion in perennial grasses.