Chapter 11 Plant p nutrition and p fertilizers
Chapter 11 Plant P nutrition and P fertilizers
Phosphorus in plant physiology P content of plants Approximately 0.2%of plant dry weight is P Plants require a relatively large amount of P. The phosphate concentration in the cytosol is maintained at fairly constant concentrations in the 5 to 8 mol/ms regardless of the external phosphate concentration except under severe P deficiency. By contrast is the vacuolar phosphate concentration
P content of plants • Approximately 0.2% of plant dry weight is P • Plants require a relatively large amount of P. The phosphate concentration in the cytosol is maintained at fairly constant concentrations in the 5 to 8 mol/m3 regardless of the external phosphate concentration except under severe P deficiency. By contrast is the vacuolar phosphate concentration. Phosphorus in plant physiology
Forms of P taken up Most P is taken up by roots as inorganic orthophosphate ions(H2 PO4 and HPO42) Roots may absorb some organic p but the amount is very small The polyphosphate(聚磷酸) was only taken up by young barley plants after hydrolysis to the orthophosphate(正磷酸) form
Forms of P taken up • Most P is taken up by roots as inorganic orthophosphate ions (H2PO4 - and HPO4 2- ) • Roots may absorb some organic P, but the amount is very small. • The polyphosphate(聚磷酸) was only taken up by young barley plants after hydrolysis to the orthophosphate(正磷酸) form
P uptake by plant H PO concentration in the root and Xylem sap is 100-1000 times greater than in the soil solution Active uptake is used to overcome this concentration gradient It is likely that inorganic P is co-transported across the plasma membrane with positively charged ions(Hf) The transport across the membrane requires energy. Wet or cold soils that reduce plant metabolic activity are likely to reduce P uptake
P uptake by plant H2PO4 - concentration in the root and xylem sap is 100-1000 times greater than in the soil solution Active uptake is used to overcome this concentration gradient. • It is likely that inorganic P is co-transported across the plasma membrane with positively charged ions (H+ ) • The transport across the membrane requires energy. Wet or cold soils that reduce plant metabolic activity are likely to reduce P uptake
P uptake by plant There are two types of transporters with different affinities for pi, one with a high affinity with a Km of 3-5 mmo/m and the other a low affinity system with a Km of 50 to 330 mmol/m3 Molecular studies have confirmed the presence of multiple genes encoding phosphate transporters that are differentially expressed
There are two types of transporters with different affinities for Pi, one with a high affinity with a Km of 3-5 mmol/m3 and the other a low affinity system with a Km of 50 to 330 mmol/m3 Molecular studies have confirmed the presence of multiple genes encoding phosphate transporters that are differentially expressed. P uptake by plant