Long Distance Transport of 14C-Putrescine in Potato Plantlets (Solanum tuberosum cv. Bintje)

Polyamines can be considered as a new class of plant growth regulators. However to be considered as hormones, they have to respond to the translocatability criterion in the whole plant. The results presented here show that a small droplet (10 µl) of ¹⁴C-putrescine supplied to a source leaf is redistributed to the whole plant. Long-distance transport occurs mainly towards young growing organs (apex, roots, stolons, tubers). Bidirectional translocation, which is also found is a result of interactions between the attractive strengths of different sinks. Heat girdling of shoots induces a strong inhibition of transport which suggests transport via the phloem. Other data, such as non labeling of mature leaves, normally fed by xylem flux and the higher content (4 to 10 times) of endogenous PA_s in phloem exudate compared with xylem exudate confirm this conclusion. After a 3 h period of transport, separation of labelled compounds by thin layer chromatography shows that the radioactivity supplied as ¹⁴C-putrescine is found as putrescine (from 64% to 82%), spermidine (from 14% to 28%) and spermine (3%) depending on the organ. This indicates that there is no important degradation of putrescine before it reaches the transport pathway.