Role of Extracellular Phosphatases in the Phosphorus-Nutrition of Clover

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Abstract
This paper examines the relationship between the ability of subterranean clover to use P-esters as sources of P for growth, and the enzymatic hydrolysis of those P-esters at the root surface. Trifolium subterraneum (cv. Mt. Barker) was grown under sterile conditions in porous agar containing either KH2PO4 (P1), 2',3'-cyclic adenosine monophosphate (cAMP) or inositol hexaphosphate (IHP) as the source of P in the medium. Subterranean clover used cAMP as well as P1 as a source of P for growth, but made little use of IHP. This preference in the use of P-esters was associated with differences in the substrate specificities of the externally accessible root phosphatases; roots of P-deficient clover grown under sterile conditions had high hydrolytic activity against cAMP but not IHP. These results are discussed in terms of an hypothesis on the function of the externally accessible phosphatases, i.e. that the phosphatases are present to recapture P from organic P compounds leaked from the cells.

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