Phosphorus in Plant Metabolism
Phosphorus is the central element in the energy metabolism of all living organisms; in this process, storage and transfer of chemical energy by formation and degradation of polyphosphate esters with adenosine take place. Phosphorus is not reduced, in contrast to nitrogen and sulfur, but remains in the highest oxidation state and is esterified in this form. It is taken up as H2PO4. In the cell phosphorus is available in this form (Pi) and binds as PC>4+ to carbohydrates forming simple phosphate esters (C-O-P, e.g. in sugar phosphate) or forming energy-rich pyrophosphate (P-P bonds) or diester bridges between carbohydrate groups (C-P-C).
Structural functions: P participates in the formation of
• RNA as a bridge between the ribose-N bases
• phospholipids of membranes.
• energy storage and transfer by polyphosphate esters with adenosine. Di- and triesters are the actual energy storage in the cell (adenosine monophosphate, AMP; adenosine diphosphate, ADP; adenosine triphosphate, ATP)
• energising of binding sites for metabolic turnover. Sugar phosphates (e.g. fructose-1,6-diphosphate) play a decisive role in the regulation of sugar metabolism and triosephos-phates are an important transport metabolite between chloroplast and cytosol (Stitt 1994).
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