ZAGóRSKA-MAREK, BEATA AND ALICJA, S. BANASIAK.* Institute of Botany, University of Wroclaw, Kanonia 6/8, 50-328 Wroclaw, Poland. - Vascular homodromy in branching shoots of conifers.
In monopodial, regularly branching system of coniferous shoot,
exemplified in our studies by Picea and Abies, the
chirality of spiral phyllotaxis in the supporting axis is correlated
either positively (homodromy) or negatively (antidromy) with that of
the laterals. As neither of these two tendencies prevailed in the
investigated material, it seemed that the supporting axis has no
effect upon the phyllotaxis of laterals. This conclusion appeared
justified especially in light of the fact that phyllotactic system of
each lateral branch is generated from the initial opposite arrangement
of prophylls. Thorough anatomical analysis of primary vascular system
structure in branching shoots of Picea and Abies
unexpectedly showed that the above conclusion should be falsified. In
vascular pattern where inclination of vascular sympodia is dependent
upon phyllotaxis and anatomic diameter of the shoot we found 100%
vascular homodromous correlation between the inclinations of vascular
sympodia in axes of all orders. This homodromy was particularly
spectacular in the cases when, in the main axis, the orientation of
sympodia was changing ontogenetically bringing up immediately the new
orientation of vascular sympodia in laterals. In the unknown way the
vascular system of the supporting axis signals the axillary meristem,
recognizing its size, what the chirality of its phyllotaxis should be,
to accommodate the same inclination of its future vascular sympodia.
These findings point out to the leading role of the vascular system in
establishing phyllotactic pattern of the shoot.
Key words: chirality, conifers, ontogeny, phyllotaxy, primary vascular system, shoot