Molecular mechanisms mediating root hydrotropism: what we have observed since the rediscovery of hydrotropism

Roots display directional growth toward moisture in response to a water potential gradient. Root hydrotropism is thought to facilitate plant adaptation to continuously changing water availability. Hydrotropism has not been as extensively studied as gravitropism. However, comparisons of hydrotropic and gravitropic responses identified mechanisms that are unique to hydrotropism. Regulatory mechanisms underlying the hydrotropic response appear to differ among different species. We recently performed molecular and genetic analyses of root hydrotropism in Arabidopsis thaliana. In this review, we summarize the current knowledge of specific mechanisms mediating root hydrotropism in several plant species.

     

Correction to: Diversity of root hydrotropism among natural variants of Arabidopsis thaliana

Journal of Plant Research -     

Vascular adaptation to microgravity: what have we learned?

Findings from recent bed rest and spaceflight human studies have indicated that the inability to adequately elevate the peripheral resistance and the altered autoregulation of cerebral vasculature are important factors in postflight orthostatic intolerance. Animal studies with rat model have revealed that simulated microgravity may induce upward and downward regulations in the structure, function, and innervation of the cerebral and hindquarter vessels. These findings substantiate in general the hypothesis that microgravity-induced redistribution of transmural pressures and flows across and within the arterial vasculature may well initiate differential adaptations of vessels in different anatomic regions. Understanding of the mechanisms involved in vascular adaptation to microgravity is also important for the development of multisystem countermeasures. However, future studies will be required to further ascertain the peripheral effector mechanism of postflight cardiovascular dysfunction.     

Pain and the placebo: what we have learned

Despite the recent blossoming of rigorous research into placebo mechanisms and the long-standing use of placebos in clinical trials, there remains widespread and profound misunderstanding of the placebo response among both practicing physicians and clinical researchers. This review identifies and clarifies areas of current confusion about the placebo response (including whether it exists at all), describes its phenomenology, and outlines recent advances in our knowledge of its underlying psychological and neural mechanisms. The focus of the review is the placebo analgesic response rather than placebo responses in general, because much of the best established clinical and experimental work to date has been done on this type of placebo response. In addition, this subfield of placebo research offers a specific neural circuit hypothesis capable of being integrated with equally rigorous experimental work on the psychological (including social psychological) and clinical levels. In this sense, placebo analgesia research bears all the marks of a genuine multilevel interdisciplinary research paradigm in the making, one that could serve as a model for research into other kinds of placebo responses, as well as into other kinds of mind-body responses.     

The different forms of flowers – what have we learned since Darwin?

Darwin's book, The Different Forms of Flowers on Plants of the Same Species, has stimulated an extraordinary amount of original research since its publication in 1877. In his book, Darwin focused primarily on heterostylous reproductive systems in flowering plants, in which two or three reproductive morphs with reciprocal placement of anthers and stigmas occur in populations. These morphs are usually self‐incompatible and cross‐incompatible with individuals possessing the same reproductive morph. Many of the papers on heterostyly published since Forms of Flowers appeared have focused on the questions raised by Darwin about the evolution and function of heterostyly. Darwin's hypothesis that heterostyly promotes cross‐pollination between different morphs has been largely substantiated, despite the difficulties in finding the ideal experimental system to address this question. Heterostyly is now known to occur in many more plant families than at the time Forms of Flowers was published and, as expected, the heterostylous syndrome is now defined more broadly than in Darwin's time. The origin of heterostyly remains an area of active research, with hypotheses stressing either the evolution of heteromorphic self‐incompatibility as the first step in the evolution of this reproductive system or, alternatively, the evolution of the reciprocal features of floral morphology. Phylogenetic approaches, combined with studies on the physiological and molecular genetic basis of heterostyly, offer promise in helping to resolve questions about the origin of heterostyly. There is no doubt that heterostyly has evolved on multiple occasions and that self‐incompatibility associated with heterostyly is unrelated to the more common multi‐allelic self‐incompatibility systems found in monomorphic species. Further progress in understanding conditions favouring evolution of heterostyly will depend on an increased understanding of the relation between the reciprocal morphological features of the breeding system and the nature of self‐incompatibility. Almost a century and a half after the appearance of The Different Forms of Flowers on Plants of the Same Species, heterostyly remains an active area of research. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 249–261.     

Wood-based building components: what have we learned?

Wood has long played a part in sheltering humans from the elements, but many of its properties remain poorly understood. This paper reviews deterioration of wood in buildings and discusses methods for preventing, detecting, and arresting decay. Research needs for reducing losses to fungal and insect attack are also addressed.     

Teleost fish osmoregulation: what have we learned since August Krogh, Homer Smith, and Ancel Keys

In the 1930s, August Krogh, Homer Smith, and Ancel Keys knew that teleost fishes were hyperosmotic to fresh water and hyposmotic to seawater, and, therefore, they were potentially salt depleted and dehydrated, respectively. Their seminal studies demonstrated that freshwater teleosts extract NaCl from the environment, while marine teleosts ingest seawater, absorb intestinal water by absorbing NaCl, and excrete the excess salt via gill transport mechanisms. During the past 70 years, their research descendents have used chemical, radioisotopic, pharmacological, cellular, and molecular techniques to further characterize the gill transport mechanisms and begin to study the signaling molecules that modulate these processes. The cellular site for these transport pathways was first described by Keys and is now known as the mitochondrion-rich cell (MRC). The model for NaCl secretion by the marine MRC is well supported, but the model for NaCl uptake by freshwater MRC is more unsettled. Importantly, these ionic uptake mechanisms also appear to be expressed in the marine gill MRC, for acid-base regulation. A large suite of potential endocrine control mechanisms have been identified, and recent evidence suggests that paracrines such as endothelin, nitric oxide, and prostaglandins might also control MRC function.     

Alveolus formation: what have we learned from genetic studies?

The respiratory system has two basic functions: air exchange and pathogen clearance. The conducting airway and alveolar parenchyma are the basic structures to fulfill these functions during respiratory cycles. In humans, there are approximately 40 cell types in the lung that coordinately work together through various structural and signaling molecules. These molecules are vital for maintaining normal lung functions in response to environmental changes. Aberrant expression of these molecules can jeopardize human health and cause various pulmonary diseases. In this article, we will review some recent progress made in the pulmonary field, using genetic animal model systems to elucidate molecular mechanisms that are important for alveolar formation and lung diseases.     

Evolutionary biology of starvation resistance: what we have learned from Drosophila

Most animals face periods of food shortage and are thus expected to evolve adaptations enhancing starvation resistance (SR). Most of our knowledge of the genetic and physiological bases of those adaptations, their evolutionary correlates and trade-offs, and patterns of within- and among-population variation, comes from studies on Drosophila. In this review, we attempt to synthesize the various facets of evolutionary biology of SR emerging from those studies. Heritable variation for SR is ubiquitous in Drosophila populations, allowing for large responses to experimental selection. Individual flies can also inducibly increase their SR in response to mild nutritional stress (dietary restriction). Both the evolutionary change and the physiological plasticity involve increased accumulation of lipids, changes in carbohydrate and lipid metabolism and reduction in reproduction. They are also typically associated with greater resistance to desiccation and oxidative stress, and with prolonged development and lifespan. These responses are increasingly seen as facets of a shift of the physiology towards a 'survival mode', which helps the animal to survive hard times. The last decade has seen a great progress in revealing the molecular bases of induced responses to starvation, and the first genes contributing to genetic variation in SR have been identified. In contrast, little progress has been made in understanding the ecological significance of SR in Drosophila; in particular it remains unclear to what extent geographical variation in SR reflect differences in natural selection acting on this trait rather than correlated responses to selection on other traits. Drosophila offers a unique opportunity for an integrated study of the manifold aspects of adaptation to nutritional stress. Given that at least some major molecular mechanisms of response to nutritional stress seem common to animals, the insights from Drosophila are likely to apply more generally than just to dipterans or insects.     

Polydomy in ants: what we know, what we think we know, and what remains to be done

The correct identification of colony boundaries is an essential prerequisite for empirical studies of ant behaviour and evolution. Ant colonies function at various organizational levels, and these boundaries may be difficult to assess. Moreover, new complexity can be generated through the presence of spatially discrete subgroups within a more or less genetically homogeneous colony, a situation called polydomy. A colony is polydomous only if individuals (workers and brood) of its constituent nests function as a social and cooperative unit and are regularly interchanged among nests. This condition was previously called polycalic, and the term polydomy was used in a broader sense for a group of daughter nests of the same mother colony (implying limited female dispersal), without regard to whether these different nests continued to exchange individuals. We think that this distinction between ‘polycaly’ and ‘polydomy’ concerns two disparate concepts. We thus prefer the narrower definition of polydomy, which groups individuals that interact socially. Does this new level of organization affect the way in which natural selection acts on social traits? Here, after examining the history of terms, we review all ant species that have been described as expressing polydomous structures. We show that there is no particular syndrome of traits predictably associated with polydomy. We detail the existing theoretical predictions and empirical results on the ecology of polydomy, and the impact of polydomy on social evolution and investment strategies, while carefully distinguishing monogynous from polygynous species. Finally, we propose a methodology for future studies and offer ideas about what remains to be done. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 319–348.