Characterization of spatial networklike patterns from junction geometry.

We propose a method for quantitative characterization of spatial networklike patterns with loops, such as surface fracture patterns, leaf vein networks, and patterns of urban streets. Such patterns are not well characterized by purely topological estimators: also patterns that both look different and result from different morphogenetic processes can have similar topology. A local geometric cue--the angles formed by the different branches at junctions--can complement topological information and allow the quantification of the large scale spatial coherence of the pattern. For patterns that grow over time, such as fracture lines on the surface of ceramics, the rank assigned by our method to each individual segment of the pattern approximates the order of appearance of that segment. We apply the method to various networklike patterns and find a continuous but sharp dichotomy between two classes of spatial networks: hierarchical and homogeneous. The former class results from a sequential growth process and presents large scale organization, and the latter presents local, but not global, organization.

Insights in the knowledge of two Argentine medicinal species of the genus Hybanthus (Violaceae) / Contribución al estudio de dos especies medicinales argentinas del género Hybanthus (Violaceae)

A differential morphoanatomical study was performed in two Argentine species: Hybanthus parviflorus and Hybanthus bigibbosus. Fresh material fixed in acetoalcoholic formalin and material from herbarium were employed. Paradermal and longitudinal sections of stems and transversal sections of leaves were prepared and stained with aqueous alcoholic safranin. The hydrochloric fluoroglucyn test was performed. Known and novel characters (distribution of vascular bundles of the primary stem and type and relative length of cover hairs and cuticular ornamentation of the adaxial epidermis, respectively) prove to be of value for the recognition of these species.Furthermore, the intestinal propulsor activity, related to the popular uses of these species was also assessed. Infusions of the whole plant, their roots and the 50 percent EtOH extracts of the aerial parts of H. parviflorus and H. bigibbosus were tested by the activated charcoal method. The extracts of H. parviflorus proved to have a significant activity which would allow validating its popular use.

Se encaró el estudio morfoanatómico diferencial de dos especies argentinas: Hybanthus parviflorus e Hybanthus bigibbosus. Se trabajó con material fresco fijado en formalina aceto-alcohólica y de herbario. Se realizaron preparados paradermales y cortes longitudinales y transversales de tallos y transversales de hoja empleando safranina alcohólico-acuosa y el test de floroglucina clorhídrica. Caracteres conocidos (distribución de haces vasculares en tallo primario) y novedosos (tipología y longitud relativa de tricomas tectores; ornamentación cuticular de la epidermis adaxial) poseen valor diferencial para el reconocimiento de estas especies.Asimismo se determinó la actividad de propulsión intestinal de ambas especies, relacionada con su uso popular. Se ensayaron las infusiones de la raíz y de las partes aéreas y el extracto EtOH 50 por ciento de las partes aéreas de H. parviflorus e H. bigibbosus, empleando el método del carbón activado. Los extractos de H. parviflorus presentaron una actividad significativa que permitiría validar su uso popular.

Marcescent corollas as functional structures: effects on the fecundity of two insect-pollinated plants.

BACKGROUND AND AIMS: Persistence of withered corollas after anthesis ('corolla marcescence') is widespread in angiosperms, yet its functional significance does not seem to have been explored for any species. This note reports the results of experiments assessing the fecundity effects of marcescent corollas in two southern Spanish insect-pollinated plants, Lavandula latifolia (Lamiaceae) and Viola cazorlensis (Violaceae). METHODS: The effect of marcescent corollas on seed production was evaluated experimentally on wild-growing plants. Newly open flowers were randomly assigned to either control or treatment groups in experimental plants. After anthesis, withered corollas of treatment flowers were removed and those in control flowers were left in place. Fruits produced by treatment and control flowers were collected shortly before dehiscence and the number of seeds counted. KEY RESULTS: In V. cazorlensis, removal of withered corollas had no effect on percentage of fruit set, but mean seeds per fruit increased from 9·5 to 11·4. In L. latifolia, corolla removal had no effect on the number of seeds per fruit, but reduced the proportion of flowers ripening fruit from 60 % to 40 %. The detrimental effect of corolla removal on L. latifolia fecundity resulted from the drastic increase in fruit infestation by seed-predatory cecidomyiid larvae, which occurred in 4 % and 34 % of control and treatment fruits, respectively. CONCLUSIONS: Because of their potential effects on plant fecundity, marcescent corollas should not be dismissed a priori as biologically irrelevant leftovers from past floral functions. The simplicity of the experimental layout required to test for short-term fecundity effects of corolla marcescence should help to achieve a better understanding of the ecological and evolutionary correlates of this widespread but poorly understood trait.

Description of a fertilization-independent obligate apomictic species: Corunastylis apostasioides Fitzg.

The Australian midge orchid Corunastylis apostasioides of the tribe Diurideae has completely eliminated any male contribution in the process of seed formation, which occurs directly from the maternal tissue by a process termed apomixis. Here, we report C. apostasioides to be an obligate apomictic species devoid of any sexuality and compare its development to a close sexual relative C. fimbriata (R. Br.) D.L. Jones & M.A. Clem. Apomictic characteristics in C. apostasioides include production of seed in absence of fertilization, frequently closed flowers, production of immature pollen in non-dehiscent anthers, expansion of ovaries despite the lack of fertilization and the absence of a citronella scent that is found in C. fimbriata produced to attract pollinating vinegar flies (Jones 2006). The nature of apomixis in C. apostasioides was examined by ovule histology and amplified fragment length polymorphism (AFLP) in each case drawing comparison with sexual C. fimbriata. In C. apostasioides the central megaspore mother cell undergoes diplosporic apomixis, while additional embryos are derived from nucellar or integument initials formed by sporophytic apomixis. Typical of apomicts, C. apostasioides is polyploid compared to the sexual C. fimbriata. The divergences of C. apostasioides from sexuality to apomictic development are discussed.

Tissue-specific expression of head-to-tail cyclized miniproteins in Violaceae and structure determination of the root cyclotide Viola hederacea root cyclotide1.

The plant cyclotides are a family of 28 to 37 amino acid miniproteins characterized by their head-to-tail cyclized peptide backbone and six absolutely conserved Cys residues arranged in a cystine knot motif: two disulfide bonds and the connecting backbone segments form a loop that is penetrated by the third disulfide bond. This knotted disulfide arrangement, together with the cyclic peptide backbone, renders the cyclotides extremely stable against enzymatic digest as well as thermal degradation, making them interesting targets for both pharmaceutical and agrochemical applications. We have examined the expression patterns of these fascinating peptides in various Viola species (Violaceae). All tissue types examined contained complex mixtures of cyclotides, with individual profiles differing significantly. We provide evidence for at least 57 novel cyclotides present in a single Viola species (Viola hederacea). Furthermore, we have isolated one cyclotide expressed only in underground parts of V. hederacea and characterized its primary and three-dimensional structure. We propose that cyclotides constitute a new family of plant defense peptides, which might constitute an even larger and, in their biological function, more diverse family than the well-known plant defensins.

Constitutive property of the local organization of leaf venation networks.

The leaf venation of dicotyledons forms complex patterns. In spite of their large variety of morphologies these patterns have common features. They are formed of a hierarchy of structures, which are connected to form a reticulum. Excellent images of these patterns can be obtained from leaves from which the soft tissues have been removed. A numerical image processing has been developed, specially designed for a quantitative analysis of this type of network. It provides a precise characterization of its geometry. The resulting data reveals a surprising property of reticula's nodes: the angles between vein segments are very well defined and it is shown that they are directly related by the radii of the segments. The relation between radii and angles can be expressed very simply using a phenomenological analogy to mechanics. This local organization principle is universal; all leaf venation patterns studied show the same behavior. The results are compared with physical networks such as fracture arrays or soap froth in terms of hierarchy and reorganization.