Progress in Botany 73 pp 161-188
Long-Distance Transport and Plant Internal Cycling of N- and S-Compounds
A coordinated supply of the whole plant with sulfur (S) and nitrogen (N) requires mechanisms to regulate not only uptake and assimilation but also long-distance transport of both nutrients in the phloem and xylem as well as the plant internal cycling of S and N compounds. In trees, plant internal nutrient cycling which includes bidirectional exchange between phloem and xylem allows to partially uncouple nutrient demand from soil supply and needs to be highly coordinated with seasonal storage and remobilisation of S- and N-compounds. In both annual and perennial plants the pools of N and S compounds cycling within the plant provide an integrated signal to adapt the nutrient supply of the plant to the actual demand.
This review discusses the transport of N and S compounds in phloem and xylem, illustrates the quantitative importance and the physiological relevance of different N and S compounds transported and focuses on the exchange between the transport systems. Thereby we demonstrate similarities and differences between N and S in assimilation, transport, storage and the underlying regulatory mechanisms.