The Relative Abundance of Mountain Pine Beetle Fungal Associates Through the Beetle Life Cycle in Pine Trees

The mountain pine beetle (MPB) is a native bark beetle of western North America that attacks pine tree species, particularly lodgepole pine. It is closely associated with the ophiostomatoid ascomycetes Grosmannia clavigera, Leptographium longiclavatum, Ophiostoma montium, and Ceratocystiopsis sp.1, with which it is symbiotically associated. To develop a better understanding of interactions between beetles, fungi, and host trees, we used target-specific DNA primers with qPCR to assess the changes in fungal associate abundance over the stages of the MPB life cycle that occur in galleries under the bark of pine trees. Multivariate analysis of covariance identified statistically significant changes in the relative abundance of the fungi over the life cycle of the MPB. Univariate analysis of covariance identified a statistically significant increase in the abundance of Ceratocystiopsis sp.1 through the beetle life cycle, and pair-wise analysis showed that this increase occurs after the larval stage. In contrast, the abundance of O. montium and Leptographium species (G. clavigera, L. longiclavatum) did not change significantly through the MPB life cycle. From these results, the only fungus showing a significant increase in relative abundance has not been formally described and has been largely ignored by other MPB studies. Although our results were from only one site, in previous studies we have shown that the fungi described were all present in at least ten sites in British Columbia. We suggest that the role of Ceratocystiopsis sp.1 in the MPB system should be explored, particularly its potential as a source of nutrients for teneral adults.     

A rapid fluorometric DNA assay for the measurement of cell density and proliferation in vitro

Summary Many research efforts require the accurate determination of cell density in vitro. However, physical cell counting is inaccurate, time-intensive and requires removal of the cells from their growth environment, thereby introducing a host of potential artifacts. The current studies document a very simple method of determining cell density in microtiter wells via DNA-enhanced fluorescence. Fixed cells are stained with the A-T intercalating DNA stains DAPI or Hoechst 33342 and then fluorescence is quantified in a plate fluorometer. Fluorescence is shown to be linearly related to cell density as determined by two physical counting methods. The validity of the method is established in determining serum-stimulated growth of smooth muscle cells and in mitogen-induced growth of endothelial cells. The fixed cells can be stored for prolonged periods, thus allowing time-course proliferation assays without interassay variations. The fixed cells are also suitable for determinations of antigens of interest by ELISA. This method is potentially valuable in many in vitro systems where the quantification of cell density and proliferation is necessary. This work supported in part by NIH Cardiovascular Training Grant HL07423 and a grant from the American Federation for Aging Research to T. M. and HL35724 to B. W. EDITOR’S STATEMENT The technique described in this paper represents an approach to quantifying cell density in adherent monolayers of cultured cells in microtiter wells that is rapid and simple and does not require radioisotopes or removal of cells.     

Regulation of Phytochrome Message Abundance in Root Caps of Maize : Spatial, Environmental, and Genetic Specificity

In many cultivars of maize (Zea mays L.) red light affects root development via the photomorphogenetic pigment phytochrome. The site of perception for the light is the root cap. In the maize cultivar Merit, we investigated phytochrome-mediated events in the cap. We established that the message encoded by the phyA1 gene was most abundant in dark-grown tissue and was asymmetrically distributed in the root cap, with greatest expression in the cells which make up the central columella core of the cap. Phytochrome message was negatively autoregulated in a specific region within the root cap. This autoregulation was sensitive to very-low-fluence red light, and thus was characterized as a phytochrome-mediated, very-low-fluence event. The kinetics of message reaccumulation in the dark were also examined and compared to the kinetics of the light requirement for root gravitropism in this cultivar. Similarly, the degree of autoregulation present in two other maize cultivars with different light requirements for gravitropic sensitivity was investigated. It appears that the Merit cultivar expresses a condition of hypersensitivity to phytochromemediated light regulation in root tissues. We conclude that phytochrome regulates many activities within the cap, but the degree to which these activities share common phytochrome-mediated steps in not known.     

Conceptual models and analytical tools: The biology of physicist Max Delbrück

Journal of the History of Biology -     

CHROMOSOME NUMBERS IN COMPOSITAE V. ASTEREAE II.

Reports of 100 new chromosome counts are made for the tribe Astereae of Compositae, mostly based on determinations of meiotic material, including first counts for 9 genera and 53 species. Counts are now available for 58 of the approximately 100–120 genera and 431 of the approximately 2000 species in the tribe. Comparisons are made between chromosome number and habit and also between chromosome number and geographical distribution. Species and genera with a basic number of x = 9 are the most abundant. Within different phyletic lines x = 9 is also the most abundant number. On the other hand, many species with x = 4 and 5, belonging to a number of small, largely annual genera, are concentrated in southwestern North America. The low chromosome number in these plants is probably correlated with the dry habitat they occupy, and is most likely a specialized condition.