¹⁴C translocation in orange plants

Abstract

Translocation patterns were studied by supplying ¹⁴CO₂ to selected source leaves under glasshouse conditions and preparing whole plant autoradiographs. The chemical nature of ¹⁴CO₂ fixation products was also examined.

Within the actively growing shoots all currently expanding leaves showed strong import of ¹⁴C assimilates but no export. Fully expanded leaves, borne either on a fruitful growth cycle or on a previous growth cycle, exported assimilates principally to nearby fruits. Sharp differences existed between adjacent fruits during their early development with respect to the level of ¹⁴C incorporation.

Mature leaves some distance from sites of current growth activity exported principally to the root system. Old leaves between the source leaf and roots failed to import. ¹⁴C-labelled sugars comprised the bulk of radioactive assimilates in leaf, stem, and fruit 24 hr after the commencement of feeding. In the roots, amino acids were the most heavily labelled fraction.

¹⁴C photosynthate appeared to be translocated as sucrose and it was this metabolite which occurred within the outer peel of the fruit.