ABSTRACT
Nitrogen is taken up by plants in the inorganic form as nitrate. ammonium ions, ammonia gas, or as nitrogen gas before nitrogen fixation begins. There is insufficient space in a chapter of this nature to cover all aspects of inorganic nitrogen assimilation in any reasonable depth, nor would it be appropriate for a text on amino acids. The subjects of nitrogen uptake and reduction will be discussed only briefly, and the reader will be directed to the most recent authoritative review articles that are available. The nitrogen content of amino acids and other organic nitrogen-containing compounds in higher plants is all derived from ammonia. which occupies a central role in plant nitrogen metabolism. For this reason (and also because of the personal bias of one of the authors, P. J. L.), we have unashamedly discussed at length, the pathway of ammonia assimilation. This chapter will consider the flow of nitrogen from ammonia through glutamine and glutamate to the other amino acids and on to some of the diverse range of nitrogenous compounds found in plants. Consideration will also be given to the effects of developmental and environmental conditions on nitrogen flow, although some of these topics are dealt with in later chapters.
