Hormone Movement in Vascular Systems

Endogenous growth regulators may be translocated in the plant s vascular systems. This would seem to hold especially true for gibberellins and cytokinins, since activity has been detected in the xylem sap of many different herbaceous as well as woody species. Obviously these hormones are also exported from photosynthesizing leaves, as indicated by their presence in sieve tube sap. Although with less frequency, also auxin and ABA-like activity have been detected in both xylem and phloem sap (Table 3.1). 

After feeding the tips of intact primary roots of Phaseolus seedlings with aqueous solutions of labeled hormones by means of 1 jil-droplets (which were quickly absorbed), percentages of 30, 10, 4, and 1 of the label from kinetin, ABA, GAi, and lAA, respectively, were translocated into the shoot system during the subsequent 24 h. Most of the shoot s kinetin label was detected in the apical bud and primary leaves, although in all cases radioactivity was found in lateral and adventitious roots, about 10% for the ABA and 3% for the other hormones (Hartung 1977). 

Xylem sap Auxins Avena, Hordeum, Sheldrake (1973c) Malus Luckwill and Whyte (1968) 

Abscisins Triticum, Zea Ricinus Zea Hall and Medlow (1974) Atkin et al. (1973) Prunus Davison and Young (1973, 1974) 

Gibberellins Helianthus Nicotiana Phaseolus Hordeum, Triticum Hoad (1975) Itai et al. (1973), Itai and Ben ZiONi (1974) Itai et al. (1973), Itai and Ben ZiONi (1974) CouiLLEROT and Bonnemain Salix Pseudo tsuga Davison (1965), Bowen and Hoad (1968), Lenton etal. (1968), Alvim et al. (1976) Lavender et al. (1973) 

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