Growth and Phosphate Transport in Barley and Tomato Plants During the Development of, and Recovery from, Phosphate-stress

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Abstract
Barley and tomato plants were cultured in nutrient solutions including 0.15 mol m−3 H2PO−4. The phosphate supply was discontinued and the subsequent effects on growth, internal phosphorus concentrations, phosphate absorption and translocation were measured at frequent intervals. Growth rates were at first unchanged and the internal phosphorus concentration decreased. During this phase the rate of phosphate transport by the roots sometimes increased significantly. Growth slowed more in shoots than in roots during a second phase of stress development and visual symptoms of deficiency appeared in tomato but not in barley. During this phase, enhancement of phosphate uptake capacity reached a maximum in both species. The subsequent decline in uptake capacity was associated with visible symptoms of deficiency developing in barley and intensifying in tomato. When stressed plants were returned to a solution containing 0.15 mol m−3 H2PO−4 rapid absorption continued for several days after the internal phosphorus concentration had returned to the level of the controls. Phosphate toxicity may have been the cause of leaf lesions and necrosis during the ‘recovery’ phase. Stomatal conductance in tomato was decreased at an early stage of stress development. Foliar-applied phosphate was absorbed more rapidly by P-stressed barley leaves than by their controls and much larger amounts were translocated from the leaves to the roots.