Translocation in plants possessing supernumerary phloem: T. ¹⁴c-assimilates AND auxin IN the INTERNAL phloem OF to BACCO (nicotiana tabacuml.)

Tobacco plants were exposed to ¹⁴CO₂ or treated with [¹⁴C]IAA in order to study the transport capacity of the internal phloem. It is shown that the translocation of assimilates in both the internal as well as the external phloem is controlled by a source-sink relationship. The internal phloem is of a lesser conductive importance in the intact plant whereas in the girdled stems it is of main importance as conductor. Auxin and other materials controlling apical dominance can also be translocated downwards in the internal phloem in a sufficient amount in order to keep axillary buds suppressed. Exogenous auxin applied to decapitated stem can also be transported via the internal phloem and bypass girdles, thus maintaining apical dominance.