14C-sucrose uptake by internode tissue

The transport and accumulation of ¹⁴C activity in decapitated, non-growing internodes of Phaseolus vulgaris L following application of ¹⁴C-sucrose or ¹⁴CO₂ is stimulated by application of auxins, cytokinins and gibberellins. The possibility that these hormone-directed effects may be mediated by stimulating the metabolism or storage of ¹⁴C-sucrose (i.e. by increasing sink demand) in the ground tissues of the stem was studied by investigations into the kinetics of ¹⁴C-sucrose uptake by thin slices of internode tissue of tomato and P. vulgaris. Sucrose uptake appears to be a carrier-mediated process, requiring active cell metabolism, and is shown to be stimulated by fusicoccin but not by indol-3yl-acetic acid (IAA). IAA only stimulates ¹⁴C-sucrose accumulation when long-distance transport is involved and it is suggested that IAA acts by stimulating the unloading of sucrose via an apoplastic pathway.