Encasement in plant morphology: an integrative approach from genes to organisms

Abstract

Recent advances in molecular genetics are prompting developmental plant morphologists to refine the theoretical context of their field. For example, at the level of the action of certain developmental genes, the distinction between recognized structural categories (i.e., stem and leaf) are not obvious. This issue has also been analyzed by morphologists from qualitative and quantitative perspectives and has lead to similar conclusions. Consequently, the classical approach to morphology with a typological view of organ categories is no longer sufficient to explain the set of all possible forms. However, within the context of a dynamic morphology, where processes of development such as growth rate, duration, and distribution are considered, a more encompassing view of the generation of form can be achieved. We therefore propose that classical morphology is a subset of dynamic morphology. The main goal of this paper is to show how new concepts and methods of viewing plant morphology allow us to build a conceptual theoretical framework that may have a predictive value with respect to morphological characteristics as well as molecular properties of organs. The main premise of this commentary, within the context of dynamic morphology, is that the plant consists of an encasement of structures or a nesting of partially similar units. Common developmental processes are in operation at each structural level and variations in the modalities of these processes lead to the development of specific structures. Repeating polymorphic sets (RPS) represent an extension of this perspective on plant development and have the potential to predict the existence of new, perhaps unknown forms. The idea of repeating polymorphic sets can also be extended to outline the activity of specific developmental genes to explain how a wide variety of those genes are interrelated during development to specify form.

Developmental morphology of branching flowers in Nymphaea prolifera

“…Flowers in angiosperms are-by definition-determinate and unbranched short-shoots. Thus, the indeterminate branching flowers of N. prolifera violate this flower definition twice, as long as we do not accept overlapping concepts such as ''inflorescence flowers'' with mixed developmental programs, as proposed and discussed by Baum and Donoghue (2002), Lacroix et al (2005), and Rutishauser and Moline (2005).…”

“…Cutter (1957b, p. 93) called the gemmae forming short shoots in Huperzia and the floral buds in Nymphaea ''topographically homologous with leaf primordia.'' Thus, a certain kind of homology (i.e., homotopy) exists between leaves and shoots (also between leaves and whole flowers), as proposed by adherents of the continuum morphology (Lacroix et al 2005;Rutishauser and Moline 2005). The topological correspondence of shoots (including flowers) and leaves in various vascular plants (e.g., Nymphaea flowers in leaf sites) may be due to uncommitted primordia that only subsequently become differentiated into shoot and leaf (as known from certain ferns), or it may be due to homeosis, i.e., ectopic expression of a shoot (or flower) completely replacing a leaf.…”

Diversity analysis of sweet potato (Ipomoea batatas [L.] Lam) germplasm from Burkina Faso using morphological and simple sequence repeats markers

“…Morphological characterization has been used extensively on various crop plants diversity assessments in many places of the world (Bos et al, 2000;Kaplan, 2001;Lacroix et al, 2005;Li et al, 2009;K'Opondo, 2011). Despite the environmental influences on plant morphology, this direct inexpensive and easy to use method of estimations was perceived as the strongest determinant of the agronomic value and taxonomic classification of plants (Li et al, 2009) and the first step in the assessment of plant diversity.…”

Classical and dynamic morphology: toward a synthesis through the space of forms

“…Recently, we proposed an alternative view of this interpretation where classical morphology is viewed as a subset of dynamic morphology (encasement of similar sub-units). This interpretation is based on the following principle discussed in detail by Lacroix et al (2005). If the limit between the categories of leaf and stem is arbitrary as stated by Sachs (1874, p.183), if processes are responsible for the elaboration of forms (Sattler 1994), and if there is a reiteration of the modalities of growth (in the sense of Jeune and Sattler 1992) common to leaves and stems (Lacroix et al 2003), it follows that the morphological unit is the shoot (i.e.…”

“…The aerial part of the plant as a whole therefore consists of a nesting, not a juxtaposition of sub-units. Following this point of view, the nesting of partially similar units is what we defined as encasement (Lacroix et al 2005). In the context of encasement, the shoot (the combination stem and leaf) is in itself the basic morphological unit.…”