Free Phytohormone Gradients in Potato Stem
as Related to Tuber Formation

T. I. Puzina and I. G. Kirillova

Department of Botany, Orel State Pedagogical University, ul. Komsomol’skaya 95, Orel, 302015 Russia

Received December 6, 1995

Abstract—Quantitative determination of cytokinins, auxins, and abscisic acid was carried out in the various
zones of potato (Solanum tuberosum L.) stem in relation to the process of tuber formation. There was a basipetal
gradient of cytokinins, and an acropetal gradient of abscisic acid, whereas the auxin gradient was reversed from
basipetal to acropetal at the flowering phase. The role of phytohormone gradients and the hormone ratio in the
regulation of assimilate transport to the shoot apex and tubers is discussed. Injection of benzyladenine and IAA
into the stem base, at the level of the first leaf, enhanced the sucrose gradient between the middle and basal stem
zones, in comparison with that of untreated plants, and favoured assimilate movement to the tubers. A conclu-
sion is made that cytokinins are predominantly involved in the process of tuber initiation, while auxin and absci-
sic acid control further tuber growth.

Key words: Solanum tuberosum - stem zones - phytohormone gradients - sucrose gradient - tuber formation

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