Virtual phyllotaxis and real plant model cases

Abstract

Abstract. Phyllotactic pattern results from genetic control of lateral primordia size (physiological or physical) relative to the size of organogenic lateral surface of shoot apical meristem (SAM). In order to understand the diversity of patterns and ontogenetic transitions of phyllotaxis we have developed a geometric model allowing changes of the above proportion in a computer simulation of SAM's growth. The results of serial simulations confirmed that many phyllotactic patterns (including most esoteric ones) and ontogenetic transitions known from real plant model cases can be easily obtained in silico. Properties of virtual patterns often deviated from those of ideal mathematical lattices but closely resembled those of the natural ones. This proved the assumptions of the model, such as initiation in the first available space or ontogenetic changes in primordia size, to be quite realistic. Confrontation of simulation results with some sequences of real phyllotactic patterns (case study Verbena) questions the autonomy of SAM in its organogenic activity and suggests the involvement of unknown signal positioning primordia in a non-random manner in the first available space.

The significance of γ-and λ-dislocations in transient states of phyllotaxis: how to get more from less – sometimes!

“…With the transition to the generative phase, the primordia of the leaves proper change their identity to inflorescence bracts or flower parts. In Epilobium [32], Verbena [21], and in a model plant Antirrhinum [33,34] vegetative phyllotaxis is decussate but it changes into helical in the inflorescence. In the floral meristems, the primordia of sepals are followed by primordia of petals, stamens, and carpels.…”

“…Separating the two main types of patterns, as useful as it is in taxonomy, does not seem to be fully justified in light of numerous observations of developmental, ontogenetic changes of one pattern into another occurring in phylogenetically different genera of plants: in Lycopodium [15], Juniperus [16], Thuja [17], Magnolia [18][19][20], Verbena [21], Anagallis [22], and many others. Taking into account that all eudicots, which have at maturity chiral phyllotaxis, start their development from an achiral, whorled pattern of opposite cotyledons, and that their flower has again a whorled architecture, which has been beautifully demonstrated for Arabidopsis [23], these transformations must be treated as natural and very common.…”

“…To do this, we performed the experiments in silico analyzing the effects of developmental changes in the sizes of lateral organ primordia. We used a previously developed, special computer program "Phyllotaxis" [21] with some new features added in the course of the study. In many variants of computer simulations, we were able to demonstrate that within the frame of general tendencies of increasing or diminishing the primordia size the fluctuations in the rate of the changes are necessary to obtain some observable effects in natural phyllotactic lattices.…”

The progressive and ancestral traits of the secondary xylem within Magnolia clad – the early diverging lineage of flowering plants

“…Usually there was only one bifurcation per plate but there were cases where even 3 bifurcating bars were observed. Other interesting aberrations resulted from the evidently 4 The Magnolia species with more than one type of perforation plate. a M. obovata -two vessel members: one with exclusively simple perforation plates (above), the second with mixed perforation plates (below).…”

“…They have both the ancestral features and those depicting specialization, therefore they lately became intensively studied. Morphological and anatomical studies gave the evidence for ancestral character and early rise of this group taking into account the number of original features such as undifferentiated perianth, numerous spirally arranged generative parts, construction of the pollen and presence of the oil cells [2][3][4][5].…”