Regulation of P uptake The concentration of phosphate cycled in phloem from shoot to root acts as a feedback signal to regulate P uptake(Drew and Saker 1984) High concentrations of phosphate in the phloem induced by low demand in shoot repress uptake Conversely low concentration associated with high shoot demand stimulate uptakeRegulation of P uptake • The concentration of phosphate cycled in phloem from shoot to root acts as a feedback signal to regulate P uptake (Drew and Saker 1984). • High concentrations of phosphate in the phloem induced by low demand in shoot repress uptake. Conversely low concentration associated with high shoot demand stimulate uptake