Effects of Nutritional Levels of Phosphate on Photosynthesis and Growth Studied with Single, Rooted Leaf of Dwarf Bean

When a single, rooted leaf of dwarf bean (Phaseolus vulgaris,var. humilis Edogawa) was grown in a phosphate-deficient conditionin light, expansion of the leaf stopped earlier than the increasein the volume of the root. These results indicate that the useof the assimilate for leaf expansion stops early in comparisonto the transport of the assimilate to the roots, when the externalsupply of phosphate is discontinued. After transfer to the phosphate-deficientcondition, the photosynthetic capacity increased for severaldays, then decreased. On the 12th day after transfer, the photosyntheticcapacity reached its lowest level. When phosphate was addedto the roots at an early stage of phosphorus deficiency, photosynthesisshowed little recovery during the first 3 hr alter the addition,but it recovered largely between 3 and 48 hr. But, at a laterdeficient stage, it was restored largely during the first 3hr, as well as being maintained between 3 and 48 hr. This immediaterecovery of photosynthesis within 3 hr after the addition ofphosphate increased largely in spite of decreasing photosynthesisin the plants subjected to progressive phosphorus-deficientstress. (Received April 2, 1981; Accepted October 23, 1981)