XVI International Botanical Congess

Accumulation rates of ABA (SABA) were measured in detached root segments dehydrated to various extents (Simonneau et al., PCE 21 1113-). SABA correlated with root water potential with a common relationship for root tips, nodal roots and branches of several ages while this was not the case if root dehydration was expressed in terms of relative water content. Delivery rates of ABA by whole root systems (JABA) were calculated and confronted to independent measurements of JABA observed in pot- and field-grown plants. Diurnal and drought-induced changes in calculated JABA followed, but slightly overestimated, observed changes in JABA. We concluded that maize roots have the capacity to supply ABA at the rates observed in the xylem stream of field-cultivated plants, even when droughted.