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40 Metabolic and Genetic Control of Nitrate, Phosphate, and Iron Assimilation in Plants

Nigel M. Crawford


Seventeen elements are known to be essential for plant growth and development. These elements are C, H, O, N, K, P, Mg, Ca, S, Fe, B, Mn, Cu, Zn, Mo, Cl, and Ni (Salisbury and Ross 1992). Some of these elements (e.g., Mo) are required at concentrations less than one part per million, but if they are absent, the plant cannot complete its life cycle. Other nutrients (the macronutrients) are needed at high levels and reach concentrations of 0.1–3% of dry weight (~3 mM–100 mM) in plant tissues (for examples, see Tables 1 and 2). These nutrients are applied as fertilizers in ever-increasing quantities as demand for more food has accelerated during this century. In the United States, $10 billion is now spent to produce 20 million tons of fertilizer every year (Glass 1989). Worldwide, more than 140 million tons of nitrogen, phosphorus, and potassium fertilizer are consumed annually (Conway and Pretty 1988). Unfortunately, much of this fertilizer leaches into ground and surface water, causing serious contamination (Conway and Pretty 1988). The study of plant mineral nutrition has become a vital component of efforts to increase the world’s food production as well as to decrease the environmental costs of our conventional agricultural practices.

Of the nutrients that plants must obtain from the soil, N, P, and Fe are often the most limited. Nitrogen is available primarily as nitrate or ammonium ions in the soil solution, although organic forms as well as nitrogen from the atmosphere can also be...

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