Secreting portion of acid phosphatase in roots of Lupin (Lupinus albus L.) and a key signal for the secretion from the roots

Abstract

Studies were carried out to identify the secreting portion of acid phosphatase (APase) in roots of lupin (Lupinus albus L.) and a key signal for the secretion from the roots. When lupin was grown in a nutrient solution without phosphate, the APase activity on the whole root surface increased and it was particularly high on the proteoid roots. When lupin was grown in a nutrient solution with 1.1 mM phosphate and transferred to a medium gel without phosphate, the activity of the secreted APase increased over the whole root system. Lupin was grown in a nutrient solution with 1.1 mM phosphate, the excised roots were transferred to a medium gel without phosphate, and the secreted APase activity was examined by activity staining of the medium gel after removal of the roots. The results indicated that the APase secretion from lupin roots was induced by a low phosphate concentration in the growth medium within 6 h. Even when the phosphate concentration in the lupin roots was sufficiently high, APase was secreted. It is concluded that a key signal for the APase secretion from lupin roots is not the low internal phosphate concentration, but the low phosphate concentration in the external solution.