Effects of drought, aging and phosphorus status on leaf acid phosphatase activity in wheat

Wheat plants grown at two levels of phosphorus supply were subjected to drought or given adequate water. Acid phosphatase activities in the youngest fully expanded leaves, and inorganic and total phosphorus concentrations in the plant tops were determined at four stages of crop development. Phosphatase activity increased with plant age, with phosphorus deficiency and with drought. Inorganic phosphorus concentration decreased with plant age and phosphorus deficiency. Drought markedly decreased the inorganic phosphorus concentration in phosphorus sufficient plants but had little effect on the concentration in deficient plants. Total phosphorus concentration increased as the plants aged and was greatest where the plants were phosphorus sufficient and adequately watered. Drought markedly reduced the total phosphorus concentration in phosphorus sufficient plants, but had little effect on the total phosphorus concentration in deficient plants. Leaf acid phosphatase activity was related inversely to the inorganic phosphorus concentration in the plant tops. Changes in activity with aging, phosphorus supply and moisture stress were associated with changes in the inorganic phosphorus concentration. An argument is developed which indicates that a single 'critical value' separating sufficient from deficient plants, either for phosphatase activity, inorganic or total phosphorus concentration, is not practicable. Different values will be required for different stages of maturity. Complications introduced by drought and aging, through their effect on phosphorus concentration and enzyme activity, were overcome by developing phosphatase zymograms. Two bands were specifically associated with phosphorus deficient plants irrespective of plant age or moisture stress. The technique offers further opportunity for studies in phosphorus metabolism and shou!d provide a useful means of diagnosing phosphorus deficiency in field groRn plants.