The origin of homochirality in molecules characterizing living systems has remained a mystery since Pasteur's recognition of the problem some 150 years ago.2-5 Most theories also assume that homochirality emerged in one class of molecules (e.g. ribose) from which it was enriched in other molecules (e.g. amino acids) as well.2-5 I propose a novel, experimentally testable hypothesis describing a process by which selective chirality in amino acids and ribonucleotides emerged simultaneously and hand-in-hand with the origin and directionality of the genetic (...) code within a system of interactions involving amino acids, peptides, nucleotide bases, their sugars and polynucleotides. BioEssays 29:689–698, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Both the physiological and the pathological morphogenetic processes that we can meet in embryogenesis, neogenesis and degenerative dysgenesis present common features: they are ruled by three different kinds of mechanisms, one related to cell migration, the second to cell differentiation and the third to cell proliferation. We deal here with an application to the cambial growth which essentially involves the third type of mechanism.Woody plants produce secondary tissue (secondary xylem and phloem) from a meristematic tissue called vascular cambium, responsible for (...) the radial growth of a tree. This paper focuses on the formation of secondary xylem, considered in two dimensions in a cross-section framework. A new discrete modelling approach is used, based on the cellular scale, in order to attain a more accurate understanding of how the elementary microscopic behaviour of each cell takes part in the macroscopic morphogenesis. The mathematical model essentially uses an occurrence method simulating the main features of radial growth with simple geometric rules, such as Thom's division rule (Thom,1972)to account for the cell proliferation. The study applies to concrete instances in which the changes made in the geometrical cellular patterns of the vascular cambium clearly affect the shape of the tree, as in Pinus radiata (D. Don.). (shrink)

We hypothesize that life began not with the first self‐reproducing molecule or metabolic network, but as a prebiotic ecology of co‐evolving populations of macromolecular aggregates (composomes). Each composome species had a particular molecular composition resulting from molecular complementarity among environmentally available prebiotic compounds. Natural selection acted on composomal species that varied in properties and functions such as stability, catalysis, fission, fusion and selective accumulation of molecules from solution. Fission permitted molecular replication based on composition rather than linear structure, while fusion (...) created composomal variability. Catalytic functions provided additional chemical novelty resulting eventually in autocatalytic and mutually catalytic networks within composomal species. Composomal autocatalysis and interdependence allowed the Darwinian co‐evolution of content and control (metabolism). The existence of chemical interfaces within complex composomes created linear templates upon which self‐reproducing molecules (such as RNA) could be synthesized, permitting the evolution of informational replication by molecular templating. Mathematical and experimental tests are proposed. BioEssays 28: 399–412, 2006. © 2006 Wiley Periodicals, Inc. (shrink)