Uptake of Inorganic Nitrogen Compounds in an Acidophilic Alga
Inorganic nitrogen compounds are often limiting for plant growth in natural environments. Their average concentration is at the micromolar level or below and can change largely with environmental stress (Raven 1980; Syrett 1981). Specific uptake systems, therefore, have been postulated and found at the plasmalemma to concentrate these compounds within the cell and thus sustain growth. Generally they are not constitutive and can be switched on when required to accommodate the environmental availability to the nutrition needs. Metabolic energy is eventually always required to maintain the uptake even if the primary transport processes can be directly driven by the electrochemical potential of the considered compound (Ullrich 1987). This is true for nitrate, the most widely available inorganic nitrogen compound for plant growth in terrestrial habitats as well as for ammonium or ureides more abundant than nitrate in thesea (Syrett 1981, 1987).
KeywordsRespiration Nitrite Polypeptide Assimilation Photosynthesis
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