The broad distribution and high colonization rates of plant roots by a variety of endophytic fungi suggest that these symbionts have an important role in the function of ecosystems. Semiarid and arid lands cover more than one-third of the terrestrial ecosystems on Earth. However, a limited number of studies have been conducted to characterize root-associated fungal communities in semiarid grasslands. We conducted a study of the fungal community associated with the roots of a dominant grass, Bouteloua gracilis, at the Sevilleta National Wildlife Refuge in New Mexico. Internal transcribed spacer ribosomal DNA sequences from roots collected in May 2005, October 2005, and January 2006 were amplified using fungal-specific primers, and a total of 630 sequences were obtained, 69% of which were novel (less than 97% similarity with respect to sequences in the NCBI database). B. gracilis roots were colonized by at least 10 different orders, including endophytic, coprophilous, mycorrhizal, saprophytic, and plant pathogenic fungi. A total of 51 operational taxonomic units (OTUs) were found, and diversity estimators did not show saturation. Despite the high diversity found within B. gracilis roots, the root-associated fungal community is dominated by a novel group of dark septate fungi (DSF) within the order Pleosporales. Microscopic analysis confirmed that B. gracilis roots are highly colonized by DSF. Other common orders colonizing the roots included Sordariales, Xylariales, and Agaricales. By contributing to drought tolerance and nutrient acquisition, DSF may be integral to the function of arid ecosystems.Symbiotic associations of fungi and plants are ancient and phylogenetically diverse (4,9,11,42,43,60,64,69). Some of these fungi, notably mycorrhizal fungi, have received extensive study, but accumulating evidence indicates that many of the fungi associated with plant roots are dark septate fungi (DSF). These fungi are usually described as endophytes, whose functions have only recently been studied (43,44,76). DSF comprise a taxonomically diverse group (34, 37) characterized by melanized septate hyphae. Endophytes with hyaline hyphae are also common (e.g., see references 48, 53, and 76), but are less well characterized, because they are more difficult to detect in microscopic analysis and are sometimes considered contaminants in mycorrhizal fungal studies. Growing evidence showing the broad distribution and high root colonization rates of DSF in different ecosystems suggests that their functional importance may rival that of arbuscular mycorrhizal fungi (AMF) (1, 43), particularly for plants growing in stressed environments, such as alpine habitats and arid grasslands (8, 45a, 54, 56, 75). In these habitats, endophytic DSF and other rootassociated fungi allow some plants to increase their resistance to drought and heat and facilitate the acquisition of nutrients (23, 43, 45a, 50, 57, 76, 81).Desert environments are one of the most challenging ecosystems for plants and microorganisms (18,51,87). Biological activity, dive...

Abstract. Ethnotraditional use of plant-derived natural products plays a significant role in the discovery and development of potential medicinal agents. Plants of the genus Taraxacum, commonly known as dandelions, have a history of use in Chinese, Arabian and Native American traditional medicine, to treat a variety of diseases including cancer. To date, however, very few studies have been reported on the anti-carcinogenic activity of Taraxacum officinale (TO). In the present study, three aqueous extracts were prepared from the mature leaves, flowers and roots, and investigated on tumor progression related processes such as proliferation and invasion. Our results show that the crude extract of dandelion leaf (DLE) decreased the growth of MCF-7/AZ breast cancer cells in an ERK-dependent manner, whereas the aqueous extracts of dandelion flower (DFE) and root (DRE) had no effect on the growth of either cell line. Furthermore, DRE was found to block invasion of MCF-7/ AZ breast cancer cells while DLE blocked the invasion of LNCaP prostate cancer cells, into collagen type I. Inhibition of invasion was further evidenced by decreased phosphorylation levels of FAK and src as well as reduced activities of matrix metalloproteinases, MMP-2 and MMP-9. This study provides new scientific data on TO and suggests that TO extracts or individual components present in the extracts may be of value as novel anti-cancer agents. IntroductionPlants of the genus Taraxacum, also known as dandelions, are members of the Asteraceae family. These perennial plants are widespread throughout the warmer temperate zones of the Northern Hemisphere and have been used for centuries as a remedy for various ailments by several societies. Dandelions play a pivotal role in traditional Chinese medicine (TCM) and are frequently used for treatment of breast, uterine and lung tumors as well as hepatitis and digestive diseases (1,2), while Native Americans use dandelion roots and herbs to treat kidney disease, dyspepsia and heartburn. In traditional Arabian medicine, dandelions have been applied to remedy liver and spleen disorders (3), whereas European herbalists authorize the use of dandelions for fever, boils, eye problems, diabetes and diarrhea (4).The variety of health benefits associated with the use of dandelions has been attributed to specific Taraxacum species as extracts of the whole plants or specific plant parts. Anticarcinogenic activities have been reported for the aqueous root extract of Taraxacum japonicum on mouse skin tumors (5). Further study revealed that taraxasterol and taraxerol, triterpenoids isolated from T. japonicum, were responsible for the observed effect on mouse skin tumors and that taraxasterol inhibited spontaneous mammary carcinogenesis, after oral administration (6). Taraxinic acid, isolated from Taraxacum coreanum showed potent antiproliferative activity against HL-60 cells (7) and the ethanolic extracts of the Chinese dandelion root (Taraxacum mongolicum) inhibited the growth of B16 2F2 mouse melanoma cells (8). Antitumor...

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Here, we show how the mechanical properties of a thick-shelled tropical seed are adapted to permit them to germinate while preventing their predation. The seed has evolved a complex heterogeneous microstructure resulting in hardness, stiffness and fracture toughness values that place the structure at the intersection of these competing selective constraints. Analyses of different damage mechanisms inflicted by beetles, squirrels and orangutans illustrate that cellular shapes and orientations ensure damage resistance to predation forces imposed across a broad range of length scales. This resistance is shown to be around the upper limit that allows cracking the shell via internal turgor pressure (i.e. germination). Thus, the seed appears to strike an exquisitely delicate adaptive balance between multiple selection pressures.

Thirty-three nuclear RFLP (restriction fragment length polymorphism) probes were used to study genetic diversity in Hawaiian and Cook Islands species of Tetramolopium for comparison with previous morphological and isozyme studies and to provide greater resolution of the events associated with adaptive radiation in the genus. Levels of RFLP diversity are greater than those reported for isozymes, yet are still low in comparison to continental species. Genetic differentiation is greatest among species in sections rather than among sections and is concordant with the hypothesis of phyletic sorting of initial variability as suggested for morphological traits. Hypothesized introgression between T. lepidotum and T. filiforme is supported, but the evidence suggests bidirectional gene flow. Systematic relationships derived from the data agree with hypotheses based on morphology in the placement of populations within their respective species and the recognition of three main lineages within Hawaii. Inclusion of the Cook Islands species, however, renders section Tetramolopium paraphyletic, contradicting morphological, ecological, and crossing evidence. Interpreting these results in light of evidence from previous studies, the genetic diversity and relationships seen among species and sections of Hawaiian and Cook Islands Tetramolopium reflect the recent and rapid evolution of this group, limited addition of new variability, and phyletic sorting.