Direct Evidence for Translocation of Sucrose in Sugarcane Leaves and Stems

Quantitative analysis shows that sucrose is the major organic constituent of phloem exudates in mlost plants (6, 8). When leaves are allowed to photosynthesize in C140, for short periodls nmost of the translocatedl radioactiv,ity is generally found in sucrose (6, 8). With respect to the nature of the transit compound in these plants there are 3 possible hypotheses whiclh are consistent with the above observations. Either A) sucrose is the transit conmpoundl, B) the substanice translocated is a derivative of sucrose which is synthesized wvithout breakdowni of the sucrose molecule, and wlhich is in rapidl eqluilibrium with sucrose in the phloemn suchl that only small quantities of the sucrose derivative are present, or C) a molecule derivable from sucrose only through breakdown is the transit molecule but, again the equilibrium relationship with sucrose being such that only a small quantity is present. The possibility that transit molecules in the phloem ma) be p)resent in small (quantities compared with nontransit molecules has been emphasized by Swanson (6) and others (3). The results reporte(l herein exclude the operation of hypothesis C) for translocatioIn in sugcar canle.