Jacqueline Lück

Patterned cell development in the secondary phloem of dicotyledonous trees: a review and a hypothesis

The secondary phloem of dicotyledonous trees and shrubs is constructed of sieve tube cells (S) and their companion cells, as well as parenchyma (P) and fibre (F) cells. Different species have characteristic sequences of these S, P and F cells within the radial files of their phloem. The sequences are recurrent, and are evidence of rhythmic cell determination and differentiation. A model was devised to account for the sequences found in various dicot tree species. It is based on the pattern of radial displacement of cells through a gradient of morphogen which supports secondary phloem development. According to this model, each tree species shows a particular pattern of post-mitotic cellular displacement along each radial file as a result of a corresponding sequence of periclinal division in the cambial initial and its descendents. The divisions and displacements ensure that at each timestep (equivalent to an interdivisional interval) each cell resides in a specific location within the morphogenic gradient. Cells then emerge from the post-mitotic zone of cell determination, having acquired different final positional values. These values lie above a series of thresholds that permit the respective determination and subsequent differentiation of one or other of the three cell types S, P and F. The recurrent nature of the sequences of the three cell types within each radial cell file, as well as their tangential banding, are a consequence of a shared rhythmic spatio-temporal pattern of periclinal cambial divisions. With a single set of morphogen parameters required for cell determination, and using three positions for cambial cell divisions, all the cellular sequences of secondary phloem illustrated in the literature can be accounted for.

A comprehensive model for acrotonic, mesotonic and basitonic branchings in plants

Topological developmental models with local (position of internodes) and global (branch lengths) characteristics are proposed to investigate the relationships between fundamental branching patterns of plants such as acrotony, mesotony, and basitony, including the coincidence of different patterns on the same plant. Modification of the basic acrotony during the development by means of, (1) the final expected main axis length results in either basitony or an extension of acrotony over a shortened main axis, (2) the final expected lateral branch length yields either lateral unlimited sympodial branching or the absence of proximal branches. Combinations of these schemes can have variable quantitative expressions on main and lateral axes.As applications, progressive morphological changes introduced by monotonic variations of parameter values give an insight into the relationships between determinate and indeterminate growth, using Lycopersicon as an example. - A theoretical framework is proposed as a possible aid for formalizing plant typology.

Generation of 3-dimensional plant bodies by double wall map and stereomap systems

The seven described archetypes of development (Table 1) cover all developmental possibilities for systems with parity and a unique cell boundary length of 4, 5, or 6 (column (a)). The geometrical constraints given by the quantification of wall lengths according to the number of segments of which they are composed, lead in some cases to 3-dimensional plant bodies described by the cellular arrangement in their epidermis. All archetypes exhibit very common botanical features. Real organisms differ essentially from archetypical ones by non uniform lifespans of cells and finite mitotic activity of most cells. The relationship between maps respecting various lifespans and the corresponding archetype will be the object of a separate publication.

Double-wall Cellworks Systems for Plant Meristems

The development of the cellular pattern of plant meristems is simulated under rules specifying a constant positioning of division walls with respect to the previously introduced wall. The network, or cellwork, of the cell walls is, in analogy to real walls, represented by double-wall labeling.

Unconventional Leaves (An Application of Map ol-Systems to Biology)

Regularities of the positioning of cell division walls during the development of meristematic plant tissues may have morphogenetic consequences. A class of developmental constructions, double wall map generating OL-systems, was explored exhaustively and accounts for the number of concevable possibilities of wall insertions. The typology over theoretical organized cell layer configurations, which has been established in earlier works on the base of these systems, is completed here by an investigation on leaf-like structures.

Repetitive cellular patterns in the secondary phloem of conifer and dicot trees, and a hypothesis for their development

Abstract The radial fusiform cell files of the secondary phloem of conifers and dicots are composed of different cell types – fibres, parenchyma and sieve cells (in conifers), or sieve elements plus companion cells (in dicots). These cell types are arranged in characteristic, species-specific sequences along the radii of the files. The sequences are replicated in adjacent files and this leads to tangential bands of similar cell type. Moreover, the sequences are developed repetitively so that a sequence found in one years growth increment of phloem is repeated in the next increment. In some species, many repetitions of the same sequence occur within one annual increment. A general hypothesis has been developed to account for the radial sequences of cell types. It is proposed that there is a gradient of a phloem-promoting morphogen, a series of morphogen thresholds for the determination of each phloem cell type, and a particular spatio-temporal pattern of periclinal cell division in the phloem domain of the vascular cambium that generates a corresponding pattern of cell displacement through the morphogen gradient in the immediately post-mitotic zone of cell determination. The feasibility of the hypothesis was supported by means of simulation which, using a constant set of initial conditions, could reproduce very nearly all the radial sequences of cell types found in the secondary phloem of a range of species of conifers and woody dicots. The tangential banding of the various cell types suggests that cell production and cell determination are events which occur synchronously across the radial files. The repeating blocks of cell types may constitute functional modules of phloem tissue, and the constituent cells probably have particular patterns of symplasmic connections and mechano-structural properties.

Cell division systems that account for the various arrangements and types of differentiated cells within the secondary phloem of conifers

There are two main types of arrangement of differentiated cells within the radial cell files of secondary phloem in conifer trees. In the C-type arrangement, characteristic of the Cupressaceae, fibre (F), parenchyma (P) and sieve (S) cells are arranged in recurrent groups, such as the “standard” cellular quartet (FSPS). In the P-type arrangement, characteristic of the Pinaceae, there are no fibres and one of the characteristic recurrent arrangements is the cellular sextet (PSSSSS). In addition, in both C-type and P-type arrangements, similar cell types are often organised into tangential bands. A simulation model, based on the theory of L-systems, was devised to account for the determination of these two types of regular and recurrent patterns of differentiated phloem cells. It was based on the supposition that, in the meristematic portion of the phloem domain, there are specific spatio-temporal patterns of periclinal cell division. When new cells are produced, those already present are displaced along the cell file, occupying a predictable number of cellular positions as a result of each round of cell division. Each cellular position is assumed to be associated with a specific value of a morphogen, such as the auxin, indole acetic acid, relevant for vascular differentiation. Using published quantitative data on the distribution auxin across the phloem, and assuming specific threshold values of auxin necessary for the determination of each cell type, it was found that sequences of F, S or P cells developed in accordance with the specific pattern of cell division and the related positional values of auxin experienced by the cells during their displacement through the immediately post-mitotic zone of cell determination. The model accounts not only for the typical C-type and P-type cellular arrangements, but also for certain variant arrangements. It provides a working example of the concepts of positional information and positional value for patterned differentiation within a developing plant tissue. There are similarities between the way groups of phloem cells develop and the differentiation of somites in the embryos of vertebrates.

Petri nets applied to experimental plant morphogenesis

Data from experiments on Erica × darleyensis and from related observations (Viemont and Beaujard, 1983) are taken for a critical analysis of the proposed model of morphogenetic phenomena. The criteria for judging the coherence of the constructions proposed in plant morphology are based on mathematical constructions deduced from Petri nets, especially elementary nets.

From Map Systems to Plant Morphogenesis

In a plant, growth is localized in some special, often distal areas, called meristems. Cell divisions and cell expansion contribute to the elongation of the axes, and also produce infinitely appendages such as leaves, stipules, and branches which are arranged in regular patterns. We want to give here a possible explanation for pattern inception in meristems on the basis of organized tissue growth.

Cellworks : An Application to Plant Morphogenesis

Cellwork-systems with double face labeling are used to investigate the division possibilities of autoreproductive tetrahedral cells. In plant morphogenesis, such cells, in apical position, are at the origin of the cell-rows which compose the shoots. The difference between 1, 2, or 3-rowed elementary theoretical shoots, with compact or tunica-like cell assemblage, can be traced back to specific orientations of the apical cells in their filiation.