Related to phyllotaxis interlocked systems of vascular sympodia and cortical resin canals in Abies and Picea shoots

Abstract

We report on some new aspects of the internal architecture of conifer shoot, proving that it is even more strongly related to phyllotaxis than was initially thought. The number of vascular sympodia in an open system of Abies and Picea shoots is correlated with the number of cortical resin canals. Both numbers are the consecutive members of the phyllotactic series, which defines the phyllotactic pattern of the shoot. This means that the concentric systems of alternately oriented vascular sympodia and resin canals are interlocked, following the course of superficial opposite parastichies. Such pattern of inner architecture most likely contributes to the mechanical strengthening of the shoot. It also provides a new example of heterogenetic induction in plant morphogenesis because the development of orderly spaced resin canals is dependent upon earlier differentiation of vascular system. A rapid method of assessing the number of vascular sympodia becomes available by means of counting the number of discrete cortical resin canals visible on the cut surface of the shoot sectioned transversely. Despite being set up on the smaller radius, the number of sympodia is always one step higher in a phyllotactic series than the number of canals.