Gibberellin transport

As reviewed in the accompanying chapters, significant progress has been achieved in elucidating the gibberellin (GA) signal transduction pathway. Yet, the hormonal nature of GA with respect to its source, transport, and sink sites remains debatable. However, compelling evidence concerning the significance of GA transport is beginning to emerge. Since plants are immobile and lack a central nervous system they use translocation of signalling molecules, mainly hormones, to maintain synchronised growth and response to environmental cues. GA belongs to this group of hormones. While addressing concerns about its local signalling, the chapter reviews the known molecular and physiological experiments that elucidate the significance of GA transport. On the basis of these findings a transport map can be proposed: maturing leaves are a potential origin of the mobile signal in the shoot, with stems and petioles, and stems and roots as routes for polar and non-polar transport, respectively. Recent findings identify GA12, a non-active GA precursor, as the major mobile GA signal for long-distance transport in Arabidopsis. The continuous cambium and fibre system, as well as unfolded leaves are important GA-signalling sinks. The chapter concludes with a discussion of the advances from GA labelling and in vivo monitoring that would facilitate future research on the GA transport mechanism and its components.