The Inflorescence Stem Fibers of <Emphasis Type="Italic">Arabidopsis thaliana Revoluta</Emphasis> (<Emphasis Type="Italic">ifl1</Emphasis>) Mutant

Arabidopsis thaliana is gradually gaining significance as a model for wood and fiber formation.revolute/ifl1 is an important mutant in this respect. To better characterize the fiber system of therevolute/ifl1 mutant, we grew plants of two alleles (rev-9 in Israel andrev-1 in the USA) and examined the fiber system of the inflorescence stems using both brightfield and polarized light. Microscopic examination of sections of plants belonging to the two different alleles clearly revealed that, contrary to previous views, in 18 (13 in Israel and 5 in Ohio) out of 30 stems (20 in Israel and 10 in Ohio) the mutant produced the primary wavy fiber system of the inflorescence stems. Our findings are further supported by the fact that fibers are seen in the figures published in other studies of the mutant even when it was stated that there were no fibers. The impression of a total lack of the wavy band of fibers is in many cases just a result of poorly lignified secondary walls. This specific gene that reduces lignification in fibers is of great significance for biotechnological developments for the paper industry and thus for the global economy and ecology. We propose thatrevoluta, the first name given to this mutant (Talbert and others 1995), is more appropriate thanifl1. Online publication: 7 April 2005     

Pines as Model Gymnosperms To Study Evolution, Wood Formation, and Perennial Growth

Pines provide a model system for the gymnosperms, an old and successful group of vascular plants that last shared a common ancestor with the angiosperms about 285 million years ago. Gymnosperms are distinct from angiosperms in their reproduction, development, metabolism, adaptations, and evolution. Pines cover vast areas of the globe, are one of the most important genera of forest trees, dominate the ecology of many temperate and subtropical forest ecosystems, and provide a major fraction of the world's wood. Here, we summarize many features of pine that make it a useful model for gymnosperms and woody plants. We also describe the influence of its reproductive system on methods for genetic analysis and the prospects for genomic studies and genetic engineering. Pines are limited as model systems by their long generation times, large size, large genomes, and the long time from fertilization to seed set.     

Olive Tree-Ring Problematic Dating: A Comparative Analysis on Santorini (Greece)

Olive trees are a classic component of Mediterranean environments and some of them are known historically to be very old. In order to evaluate the possibility to use olive tree-rings for dendrochronology, we examined by various methods the reliability of olive tree-rings identification. Dendrochronological analyses of olive trees growing on the Aegean island Santorini (Greece) show that the determination of the number of tree-rings is impossible because of intra-annual wood density fluctuations, variability in tree-ring boundary structure, and restriction of its cambial activity to shifting sectors of the circumference, causing the tree-ring sequences along radii of the same cross section to differ.     

Plant Domestication and Crop Evolution in the Near East: On Events and Processes

Reconstructing the evolutionary history of crop plants is fundamental for understanding their adaptation profile and the genetic basis of yield-limiting factors, which in turn are critical for future crop improvement. A major topic in this field is the recent claim for a millennia-long ‘protracted’ domestication process. Here we evaluate the evidence for the protracted domestication model in light of published archaeobotanical data, experimental evidence and the biology of the Near Eastern crops and their wild progenitors. The crux of our discussion is the differentiation between events or ‘domestication episodes’ and the later following crop evolutionary processes under domestication (frequently termed ‘crop improvement stage’), which are by definition, still ongoing. We argue that by assuming a protracted millennia-long domestication process, one needlessly opts to operate within an intellectual framework that does not allow differentiating between the decisive (critical) domestication traits and their respective loci, and those that have evolved later during the crop dissemination and improvement following the episodic domestication event. Therefore, in our view, apart from the lack of experimental evidence to support it, the protracted domestication assumption undermines the resolution power of the study of both plant domestication and crop evolution, from the cultural as well as from the biological perspectives.     

Does bee or wasp mimicry by orchid flowers also deter herbivores?

General visual bee mimicry and specific chemical mimicry by flowers to solitary female bees or wasps are well known in several orchid genera, for example, the Mediterranean genus Ophrys, the Australian genera Cryptostylis and Chiloglottis, and the South-African Disa. This mimicry has been shown to attract solitary male bees or wasps, which are their species-specific pollinators. The visual and chemical signals are considered to be a type of deceptive pollination mechanism based on mimicry for the exploitation of perceptual biases of animals. We propose that in addition to this unique pollination mechanism, these plants exhibit another, rarely mentioned and practically forgotten, non-exclusive function of bee or wasp mimicry (Batesian mimicry). This mimicry may deter large mammalian herbivores, and possibly also insects from the plants and especially from their flowers by a type of visual and olfactory deceptive aposematism. While visiting the flowers, bees and wasps may add a Müllerian effect to this defense. We extend this hypothesis to many other rewarding flowers that are bee or wasp pollinated and propose that abundance of pollinating bees or wasps may deter herbivorous mammals and insects from the plants during their peak flowering season.     

A critical review of the protracted domestication model for Near-Eastern founder crops: linear regression, long-distance gene flow, archaeological, and archaeobotanical evidence

The recent review by Fuller et al. (2012a) in this journal is part of a series of papers maintaining that plant domestication in the Near East was a slow process lasting circa 4000?years and occurring independently in different locations across the Fertile Crescent. Their protracted domestication scenario is based entirely on linear regression derived from the percentage of domesticated plant remains at specific archaeological sites and the age of these sites themselves. This paper discusses why estimates like haldanes and darwins cannot be applied to the seven founder crops in the Near East (einkorn and emmer wheat, barley, peas, chickpeas, lentils, and bitter vetch). All of these crops are self-fertilizing plants and for this reason they do not fulfil the requirements for performing calculations of this kind. In addition, the percentage of domesticates at any site may be the result of factors other than those that affect the selection for domesticates growing in the surrounding area. These factors are unlikely to have been similar across prehistoric sites of habitation, societies, and millennia. The conclusion here is that single crop analyses are necessary rather than general reviews drawing on regression analyses based on erroneous assumptions. The fact that all seven of these founder crops are self-fertilizers should be incorporated into a comprehensive domestication scenario for the Near East, as self-fertilization naturally isolates domesticates from their wild progenitors.     

Plant Fiber Formation: State of the Art,Recent and Expected Progress,and Open Questions

Plant fibers are one of the most important renewable resources, used as raw material in the paper industry, and for various textiles and for composites. Fibers are structural components in timber and an energy-rich component of fuel-wood. For the plant itself, fibers are important in establishing plant architecture, as a source of mechanical support, in defence from herbivory, and in some cases as elements with contractile properties, resembling those of muscles. In addition, fibers may store ergastic carbon resources and water. Here, we review various aspects of fiber development such as initiation, elongation, cell wall formation and multinuclearity, discuss open questions and propose directions for further research. Most of the recent progress in fiber formation biology, especially in cell wall structure and chemistry, emerged from studies of only a few model plants including flax, Populus spp., Eucalyptus spp., Arabidopsis thaliana and hemp. Considering the enormous importance of fibers to humanity, it is surprising how little is known about the biology of fiber formation.     

Inhibitory NK Receptor Recognition of HLA-G: Regulation by Contact Residues and by Cell Specific Expression at the Fetal-Maternal Interface

The non-classical HLA-G protein is distinguished from the classical MHC class I molecules by its expression pattern, low polymorphism and its ability to form complexes on the cell surface. The special role of HLA-G in the maternal-fetal interface has been attributed to its ability to interact with specific receptors found on maternal immune cells. However this interaction is restricted to a limited number of receptors. In this study we elucidate the reason for this phenomenon by comparing the specific contact residues responsible for MHC-KIR interactions. This alignment revealed a marked difference between the HLA-G molecule and other MHC class I molecules. By mutating these residues to the equivalent classical MHC residues, the HLA-G molecule regained an ability of interacting with KIR inhibitory receptors found on NK cells derived either from peripheral blood or from the decidua. Functional NK killing assays further substantiated the binding results. Furthermore, double immunofluorescent staining of placental sections revealed that while the conformed form of HLA-G was expressed in all extravillous trophoblasts, the free heavy chain form of HLA-G was expressed in more distal cells of the column, the invasion front. Overall we suggest that HLA-G protein evolved to interact with only some of the NK inhibitory receptors thus allowing a control of inhibition, while permitting appropriate NK cell cytokine and growth factor production necessary for a viable maternal fetal interface.