As with low-P-plants salt stress increased ABA synthesis in roots and associated transport in the xylem. However, salinity caused a distinctly greater accumulation of ABA in the leaves, stem segments and the apex than in P-deficient plants. As opposed to P deficiency, ABA export in the phloem from the leaves was stimulated by salinity. Modelling of ABA flows within an individual leaf over its life cycle showed that young growing leaves imported ABA from both phloem and xylem, whereas the adult non-senescent leaves were a source of ABA and thus provided a potential shoot-to-root stress signal as well as an acceptor for reciprocal signals from root to shoot. In senescing leaves ABA flows and accumulation were somewhat retarded and ABA was lost in net terms by export from the leaf.