The plant as a biomechatronic system

Our vision of plants is changing dramatically: from insensitive and static objects to complex living beings able to sense the environment and to use the information collected to adapt their behavior. At all times humans imitate ideas and concepts from nature to resolve technological problems. Solutions coming from plants have the potential to face challenges and difficulties of modern engineering design. Characteristic concepts of the plant world such as reiteration, modularity and swarm behavior could be of great help resolving technological problems. On the other hand a biorobotic approach would facilitate the resolution of many biological problems. In this paper, the concept of a plant-inspired robot is proposed for the investigation of both biological and technological issues.     

Bone marrow as a major lymphoid organ in Rana.

The bone marrow of adult frogs (Rana pipiens and R. catesbeiana) contains leukocytes equivalent in number to those present in the spleen. As in the spleen, a high percentage of these cells are morphologically identified as lymphocytes, and the bulk of these can be categorized as small or medium lymphocytes. In young frogs (R. catesbeiana), the ratio of marrow to spleen leukocytes is considerably greater than in adults, and in limited comparisons a high percentage of lymphocytes are found. A comparison of adult marrow and spleen anti-TNP (trinitrophenyl) plaque-forming cell responses at various days early in the response indicates that in the majority of animals marrow normally produces a larger total primary response.     

Transport viewed as a catalytic process

Transport catalysis is analysed in terms of the "induced transition fit" (ITF) concept. The essentials of ITF are briefly elucidated, emphasizing the difference of substrate-protein interactions between enzymes and carriers exemplified by the paradigm ADP/ATP carrier (AAC). Two of the numerous applications of the ITF are discussed in more detail: unidirectional passive and active transport and the relation of substrate site type inhibitors to the carrier conformations. According to ITF in most cases of unidirectional transport intrinsic binding energies may be insufficient for transport catalysis and requires additional energy from ATP or electrochemical gradients. The impacts of external energy on the carrier cycle are examined for ABC transporters (mdr) and for cation-substrate co-transporters (LacY). The relations of inhibitors to the binding site of the carrier are discussed, given the paradigm examples of side specific inhibitors of the AAC. Results with the AAC suggest the induction of an abortive ground state by inhibitors, representing extreme side specific conformation of the binding center.     

Mycobacterium tuberculosis as viewed through a computer

Mathematical models are emerging as important tools in the study of microbiology. As an illustrative example, we present results from several models each generated to study the interaction of Mycobacterium tuberculosis and the immune system. Different mathematical models were formulated on the basis of assumptions regarding system-component interactions, enabling us to explore specific aspects at diverse biological scales (e.g. intracellular, cell-cell interactions, and cell population dynamics). In addition, we were able to examine both temporal and spatial aspects. At each scale, there were consistent themes that emerged as determinative in infection outcome. Factors we identified include both host and microbial characteristics. The use of the models lies in generating hypotheses that can then be tested experimentally. Here, we outline the primary host and bacterial factors that we have identified as key mechanisms that contribute to the success of M. tuberculosis as a human pathogen. Our goal is to stimulate experimentation and foster collaborations between theoretical and experimental scientists.     

History of phage research as viewed by a European

Abstract: The history of phage research as the origin of molecular biology is related as seen by a scientist located at that critical time in Geneva. The preponderant influence of Max Delbrück on these developments is traced as a consequence of his personal charisma. Jean Weigle, former professor of experimental physics in Geneva and later research fellow with Delbrück, acted as an important ambassador to the European groups.     

The Darwinian revolution as viewed by a philosophical biologist

Darwin proclaimed his own work revolutionary. His revolution, however, is still in progress, and the changes that are going on are reflected in the contemporary historical and philosophical literature, including that written by scientists. The changes have taken place at different levels, and have tended to occur at the more superficial ones. The new ontology that arose as a consequence of the realization that species are individuals at once provides an analytical tool for explaining what has been happening and an example of the kind of changes that seem in order. It provides a clear distinction between the roles of history and of laws of nature. Pre-Darwinian evolution was superficial in the sense that it treated change as either as something pre-ordained or else due to timeless laws of nature, rather than historical contingency. Darwinism puts the ontological emphasis upon concrete, particular things (individuals) and therefore delegitimizes both essentialistic and teleological ways of thinking. However, traditional ways of thinking have persisted, if not explicitly, then often as assumptions and procedures that are merely implicit or even unconscious. As a result, anti-evolutionary attitudes continue to influence the practice of evolutionary biology as well as the study of its history and philosophy.     

Mutagenesis as viewed from another perspective

Mutation has generally been considered a random process, not directed. Thus, a mechanism allowing for adaptively responsive mutagenesis has conceptually been precluded. However, an adaptively directed mutagenesis in response to environmental stress can be based upon genetic mutator systems. Such systems, known for years, have been seen as exceptional and not considered in terms of an adaptively responsive mutagenesis. Environmental stress which invokes this type of mutagenesis can thus be regarded as mutagenic itself, and our concept of what is mutagenic must therefore be broadened. Relevant matters are also discussed.     

On some principles of evolution viewed as a stochastic process

From current stochastic models of population evolution it may be concluded that all populations of limited size will asymptotically die out. This conclusion underestimates the power of genetic evolution. In the model described in this paper, the infinitely long existence of a population of limited size is possible through its increased fitness due to the infinite perfectability of its genetic structure. Definitions of some population features, which generalize variability of known evolving units (mutation), inheritance, selection and ability to widen the range of environmental conditions where existence is possible, are introduced. It is shown that the presence of each of these features in a population of limited size is the condition necessary for its asymptotic non-extinction with positive probability. The necessary and sufficient condition that there be a positive probability that a population will not ultimately become extinct is also obtained.     

Variable place-cell coupling to a continuously viewed stimulus: evidence that the hippocampus acts as a perceptual system.

A key feature of perception is that the interpretation of a single, continuously available stimulus can change from time to time. This aspect of perception is well illustrated by the use of ambiguous figures that can be seen in two different ways. When people view such a stimulus they almost universally describe what they are seeing as jumping between two states. If it is agreed that this perceptual phenomenon is causally linked to the activity of nerve cells, the state jumps would have to occur in conjunction with changes in neural activity somewhere in the nervous system. Our experiments suggest that hippocampal place cells are part of a perceptual system. We conducted variations of a ''cue-card rotation'' experiment on rats in which the angular position of a prominent visual stimulus on the wall of cylinder is changed in the rat''s presence. The three main results are that (i) place-cell firing fields remain stationary if the cue is rotated by 180 degrees, so the relation between the cue and the field is altered; (ii) firing fields rotate by 45 degrees when the cue is rotated by 45 degrees, so the relation between the field and the card is maintained; and (iii) if the cue is first rotated by 180 degrees and then rotated in a series of 45 degrees steps, the field winds up at a different angular position relative to the card when the card is back in its original position. Thus, place cells can fire in two different ways in response to a continuously viewed stimulus. We conclude that place cells reveal that the hippocampal mapping system also has properties expected of a perceptual system.     

Microtubules viewed as molecular ant colonies

Populations of ants and other social insects self-organize and develop 'emergent' properties through stigmergy in which individual ants communicate with one another via chemical trails of pheromones that attract or repulse other ants. In this way, sophisticated properties and functions develop. Under appropriate conditions, in vitro microtubule preparations, initially comprised of only tubulin and GTP, behave in a similar manner. They self-organize and develop other higher-level emergent phenomena by a process where individual microtubules are coupled together by the chemical trails they produce by their own reactive growing and shrinking. This behaviour is described and compared with the behaviour of ant colonies. Viewing microtubules as populations of molecular ants may provide new insights as to how the cytoskeleton may spontaneously develop high-level functions. It is plausible that such processes occur during the early stages of embryogenesis and in cells.     

Genetic basis of yield as viewed from a crop physiologist's perspective

The final yield of a crop is the product of growth during the growing season and a number of developmental processes occurring throughout the life cycle of a crop, with most genes influencing the final outcome to a degree. However, recent advances in molecular biology have developed the potential to identify and map many genes or QTLs related to various important traits, including yield, plant adaptation and tolerance to stresses. Significant G×E interactions for yield have been identified, as have interactions associated with QTLs for yield. However, there is little evidence available to confirm that a QTL for yield from a parental line in one mapping population may improve yield when transferred into an adapted, high‐yielding line of another population. In order to narrow the apparent gap between the genotype and the phenotype with regard to yield, it is important to identify key traits related to yield and then attempt to identify and locate the genes controlling them. The partitioning of the developmental time to anthesis into different phases: from sowing to the onset of stem elongation and from then to anthesis, as a relatively simple physiological attribute putatively related to yield, is discussed. If the relationship holds in a wider range of conditions and the genetic factors responsible are located then the genetic basis of yield should be identified. There has also been significant progress in crop simulation modelling. Using knowledge of crop physiology and empirical relationships these models can simulate the performance of crops, including the G×E interactions. Such models require information regarding the genetic basis of yield, which are included in the form of genetic coefficients. Essentially models are constructed as decision‐making tools for management but may be of use in detecting prospective traits for selection within a breeding programme. Problems associated with this approach are discussed. This review discusses the need to use crop physiology approaches to analyse components of yield in order to reliably identify the genetic basis of yield.     

The Japanese knotweed invasion viewed as a vast unintentional hybridisation experiment

Chromosome counts of plants grown from open-pollinated seed from Japanese knotweed around the world have revealed the presence of extensive hybridisation with both native and other introduced taxa. These hybrids fit into three categories: inter- and intraspecific hybrids involving the taxa of Fallopia section Reynoutria (giant knotweeds), hybrids between Japanese knotweed and F. baldschuanica (Regel) Holub and hybrids between Japanese knotweed and the Australasian endemics of the genus Muehlenbeckia. In this minireview, the viability of the different classes of hybrid and the potential threats they pose are discussed in the context of recent examples of allopolyploid speciation, which generally involve hybridisation between a native and an alien species. Such wide hybridisations also challenge accepted taxonomic classifications. Japanese knotweed s.l. provides a fascinating example of the interplay between ploidy level, hybridisation and alien plant invasion. The octoploid (2n=88) Fallopia japonica var. japonica (Houtt.) Ronse Decraene is a single female clone throughout much of its adventive range, and provides an ideal system for investigating the potential for wide hybridisation.