Phosphate serves as the carrier of chemical energy in the plant;
Phosphate is not reduced in plants, but used in polyphosphate esters.
the soil solution. Despite this, transport in the xylem is as Pr
Pi occurs in the cell as substrate, as well as product, in all activations and enzyme reactions with ATP and ADP and simultaneously regulates many enzyme reactions. Because of this important physiological activity, the concentration of Pi in the cytosol is regulated in a very narrow range, 4-6 mmol 1_1, the vacuole serves as storage site. The relative concentration of in the cytosol and chloroplasts regulates (together with the concentration of sucrose in the cytosol) the formation of starch in the chloroplast (Fig. 2.3.14).
Phosphate is stored in plants in the form of polyphosphates or as sugar esters; in phytate up to six phosphate molecules may be deposited on one sugar (myoinositol). This form of storage is very important in seeds.
of reduced cell growth, increased root growth, dark green colouration of leaves and reddish colouring of needles with chlorosis and premature ageing. • excess: does not occur naturally because phosphate is not easily dissolved and may be regulated by polyphosphate formation.
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