Over the past 20 yr much has been learned about a unique symbiotic interaction between fungal endophytes and grasses. The fungi (Clavicipitaceae, Ascomycota) grow intercellularly and systemically in aboveground plant parts. Vertically transmitted asexual endophytes forming asymptomatic infections of cool-season grasses have been repeatedly derived from sexual species that abort host inflorescences. The phylogenetic distribution of seed-transmitted endophytes is strongly suggestive of cocladogenesis with their hosts. Molecular evidence indicates that many seed-transmitted endophytes are interspecific hybrids. Superinfection may result in hyphal fusion and parasexual recombination. Most endophytes produce one or more alkaloid classes that likely play some role in defending the host plant against pests. Hybridization may have led to the proliferation of alkaloid-production genes among asexual endophytes, favoring hybrids. The ergot alkaloid ergovaline, lolitrems, and lolines are produced by only a single sexual species, Epichloë festucae, but they are common in seed-transmitted endophytes, suggesting that E. festucae contributed genes for their synthesis. Asexual hybrids may also be favored by the counteracting of the accumulation of deleterious mutations (Muller's rachet). Endophyte infection can provide other benefits, such as enhanced drought tolerance, photosynthetic rate, and growth. Estimates of infection frequency have revealed variable levels of infection with especially high prevalence in the subfamily Pooideae. Longitudinal studies suggest that the prevalence of seed-transmitted endophytes can increase rapidly over time. In field experiments, infected tall fescue suppressed other grasses and forbs relative to uninfected fescue and supported lower consumer populations. Unlike other widespread plant/microbial symbioses based on the acquisition of mineral resources, grass/endophyte associations are based primarily on protection of the host from biotic and abiotic stresses.

When peripheral blood stem cell (PBSC) concentrates are used for allogeneic transplants, two or more apheresis procedures must often be performed. To determine how many cells could be collected from healthy people by two back-to-back apheresis procedures and what effect these collections would have on donors, we gave 19 healthy people 5 micrograms kg-1 day-1 and 21 people 10 micrograms kg-1 day-1 of granulocyte colony stimulating factor, filgrastim, for 5 days. We then collected two PBSC concentrates, one on day 5 and one on day 6. A third group of six people was given filgrastim 10 micrograms kg-1 day-1 for 5 days but had no PBSC concentrates collected. PBSC concentrate cell counts and donor cell counts, symptoms, and blood chemistries were assessed for up to 1 year. On day 5, three times more CD34+ cells were collected from donors given 10 micrograms kg-1 day-1 than those given 5 micrograms kg-1 day-1 (P = 0.009) but on day 6 the quantity of cells collected was the same (P = 0.23). The total number of CD34+ cells collected was two times greater in donors given the higher dose of filgrastim (median = 579 x 10(6); range = 174-1639 x 10(6) compared to 237 x 10(6); 103-1670 x 10(6); P = 0.061). Platelet counts fell after each PBSC concentrate collection, but there were no differences between the two groups of donors in platelet counts measured immediately after each collection. The platelet counts also fell in people who did not donate PBSC concentrates. The lowest counts in all three groups of people also occurred on day 10. In PBSC donors given 10 micrograms kg-1 day-1 of filgrastim the absolute neutrophil count (ANC) fell below premobilization counts on day 14. In donors given 5 micrograms kg-1 day-1 the ANC fell below premobilization counts on days 21, 28 and 49, CD34+ cell counts were significantly lower than premobilization counts on days 14 and 28 in donors given 10 micrograms kg-1 day-1 of filgrastim and on day 14 in those given 5 micrograms kg-1 day-1. No decrease in neutrophil or CD34+ cell counts occurred after filgrastim was given in the people who did not donate PBSC concentrates. The incidence of symptoms was similar in both groups of PBSC concentrate donors, except that those given 10 micrograms kg-1 day-1 were more than twice as likely to experience myalgias as those receiving the lower dose (P = 0.029). Several blood chemistries changed. Levels of alkaline phosphatase, LDH, SGPT, SGOT, uric acid and sodium increased. Levels of bilirubin, total protein, potassium, calcium and chloride decreased. In conclusion, twice as many CD34+ cells were collected from donors given 10 micrograms kg-1 day-1 of filgrastim. Platelet, neutrophil and CD34+ cell counts fell after the PBSC concentrate collections. The fall in platelet counts was due to both the collection and the administration of filgrastim. The falls in neutrophil and CD34+ cell counts were due to the loss of haematopoietic progenitor cells in the PBSC concentrates. Allogeneic PBSC concentrate donors should be given 10 micrograms kg-1 day-1 of filgras...

The continuum hypothesis predicts that parasites should evolve reduced virulence if they have higher opportunity for vertical transmission. However, when there is a trade-off between virulence and vertical transmission, selection may favor horizontal transmission and higher virulence. Atkinsonella hypoxylon is a fungal pathogen that reduces Danthonia fitness by 50% or more when it completely castrates hosts' chasmogamous inflorescences, despite the high opportunity for vertical transmission through cleistogamous seeds. Sporadically, infected hosts with partially castrated inflorescences (which have higher fecundity than completely castrated hosts) are observed in natural populations. Why are partially castrated plants rare if selection favors reduced virulence? We investigated whether there was genetic diversity for virulence among A. hypoxylon genotypes and the relationship between virulence and vertical transmission. We found that the fungal genotype significantly affects the occurrence of partial castration in Danthonia compressa. The proportion of seedlings that were vertically infected by their maternal plant was lower for partially castrated than for completely castrated plants. Our results demonstrate a trade-off between virulence and vertical transmission, explaining the maintenance of more virulent, completely castrating fungal genotypes in natural populations, and suggest that vertical transmission in plants is more complex than what is considered in current models.

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