Factors controlling fruit set in hermaphroditic plants: Studies with the Australian proteaceae

The number of fruits produced by many hermaphroditic plants is usually far fewer than the number of flowers available for fertilization. There are various possible explanations for the low fruit:flower ratio, some proximate and others ultimate. Recent studies, especially in northern hemisphere systems, have used field experiments to test some of them, but there are potential difficulties with the methodology of some experiments and with the testing of ultimate hypotheses. It is important to examine the possible explanations for low fruit: flower ratios with a range of different systems. This article reviews studies on Australian species of woody, perennial shrubs in the family Proteaceae; this evolutionarily distinct group of plants and pollinators has several unusual and interesting characteristics, and provides a valuable addition to the better-known northern hemisphere studies.     

Dietary unsaturated fatty acids: interactions and possible needs in relation to eicosanoid synthesis

In addition to providing energy and essential fatty acids, dietary fatty acids can affect numerous biochemical and physiologic reactions related to secretory, cardiovascular, and immune functions. The major dietary unsaturated fatty acid, linoleic acid, affects tissue arachidonic acid and can influence eicosanoid-mediated reactions. Chronic, excess, or imbalanced eicosanoid synthesis may be conductive to excessive inflammation, thrombotic tendencies, atherosclerosis, and immune suppression. Dietary n-3 polyunsaturated fatty acids (PUFAs) may ameliorate eicosanoid-related phenomena by reducing tissue arachidonic acid and by inhibiting eicosanoid synthesis. This review summarizes information concerning the metabolism of unsaturated fatty acids, with emphasis on tissue arachidonic acid levels and eicosanoids, and discusses the need for data concerning the appropriate intake of dietary n-6 and n-3 PUFAs to modulate arachidonic acid and eicosanoid synthesis and to minimize possible adverse reactions.     

Analysis of E1A-mediated growth regulation functions: binding of the 300-kilodalton cellular product correlates with E1A enhancer repression function and DNA synthesis-inducing activity.

Adenovirus E1A transforming function requires two distinct regions of the protein. Transforming activity is closely linked with the presence of a region designated conserved domain 2 and the ability of this region to bind the product of the cellular retinoblastoma tumor suppressor gene. We have investigated the biological properties of the second transforming region of E1A, which is located near the N terminus. Transformation-defective mutants containing deletions in the N terminus (deletion of residues between amino acids 2 and 36) were deficient in the ability to induce DNA synthesis and repress insulin enhancer-stimulated activity. The function of the N-terminal region correlated closely with binding of the 300-kilodalton E1A-associated protein and not with binding of the retinoblastoma protein. These results indicate that transformation by E1A is mediated by two functionally independent regions of the protein which interact with different specific cellular proteins and suggest that the 300-kilodalton E1A-associated protein plays a major role in E1A-mediated cell growth control mechanisms.     

The impact of wildfire on vesicular-arbuscular mycorrhizal fungi and their potential to influence the re-establishment of post-fire plant communities

Wildfires are a typical event in many Australian plant communities. Vesicular-arbuscular mycorrhizal (VAM) fungi are important for plant growth in many communities, especially on infertile soils, yet few studies have examined the impact of wildfire on the infectivity of VAM fungi. This study took the opportunity offered by a wildfire to compare the infectivity and abundance of spores of VAM fungi from: (i) pre-fire and post-fire sites, and (ii) post-fire burned and unburned sites. Pre-fire samples had been taken in May 1990 and mid-December 1990 as part of another study. A wildfire of moderate intensity burned the site in late December 1990. Post-fire samples were taken from burned and unburned areas immediately after the fire and 6 months after the fire. A bioassay was used to examine the infectivity of VAM fungi. The post-fire soil produced significantly less VAM infection than the pre-fire soil. However, no difference was observed between colonization of plant roots by VAM fungi in soil taken from post-fire burned and adjacent unburned plots. Soil samples taken 6 months after the fire produced significantly more VAM than corresponding soil samples taken one year earlier. Spore numbers were quantified be wet-sieving and decanting of 100-g, air-dried soil subsamples and microscopic examination. For the most abundant spore type, spore numbers were significantly lower immediately post-fire. However, no significant difference in spore numbers was observed between post-fire burned and unburned plots. Six months after the fire, spore numbers were the same as the corresponding samples taken 1 year earlier. All plants appearing in the burned site resprouted from underground organs. All post-fire plant species recorded to have mycorrhizal associations before the fire had the same associations after the fire, except for species of Conospermum (Proteaceae), which lacked internal vesicles in cortical cells in the post-fire samples.     

Cytological and molecular characterization of a chromosome interchange and addition lines in Cadet involving chromosome 5B of wheat and 6Ag of Lophopyrum ponticum

Efforts to transfer wheat curl mite (Eriophyes tulipae Keifer) resistance from Lophopyrum ponticum 10X (Podb.) Love to bread wheat (Triticum aestivum L.) have resulted in the production of a number of cytogenetic stocks, including an addition line of 6Ag, a ditelo addition line, and a wheat-Lophopyrum translocation line. Characterization of these lines with C-banding, in situ hybridization with a Lophopyrum species-specific repetitive DNA probe (pLeUCD2), and Southern blotting with pLeUCD2 and a 5S ribosomal DNA probe (pScT7) confirmed that the distal portion of the short arm of 6Ag was translocated onto the distal portion of 5BS (5BL. 5BS-6AgS). It was also determined that the ditelo addition was an acrocentric chromosome of 6AgS.     

Characterization of a region of the IncHI2 plasmid R478 which protects Escherichia coli from toxic effects specified by components of the tellurite, phage, and colicin resistance cluster.

The IncHI2 plasmid R478 specifies resistance to potassium tellurite (Te(r)), to some bacteriophages (Phi), and to pore-forming colicins (PacB). The genes encoding the three phenotypes are linked, and an 8.4-kb fragment of R478 DNA encoding them cannot be subcloned unless cocloned with a second section of the plasmid. Subclone pKFW4A contains a 5.9-kb BamHI-EcoRI fragment which caused some toxicity when present in Escherichia coli cells. Bacterial cells containing freshly transformed pKFW4A, examined by light microscopy and electron microscopy, had a filamentous morphology consistent with a block in septation. Insertion of transposon Tn1000 into terZ, -A, -B, and -C genes of pKFW4A resulted in the loss of the filamentation phenotype. Deletion of several regions of the clone confirmed that these latter components are involved in the filamentation phenotype. The region specifying protection from toxicity caused by the larger 8.4-kb fragment (encompassing this cluster and the entire 5.9-kb section of pKFW4A) was sequenced and analyzed by T7 polymerase expression and Tn1000 mutagenesis. Three open reading frames, terW, terY, and terX, were identified in a 2.6-kb region. Two polypeptides with approximate molecular masses of 18 and 28 kDa were expressed in CSRDE3 cells and were consistent with TerW (17.1 kDa; 155 amino acids [aa]) and TerY (26.9 kDa; 248 aa), whereas a protein of 213 aa deduced from terX was not observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The terX gene product shows strong identity with the previously identified TerE, TerD, and TerZ polypeptides, and there is a conserved motif of 13 residues, GDN(R/L)TG(E/A)GDGDDE, within this group of polypeptides. Complementation analysis indicated that terW, located approximately 6.0 kb upstream of terZ, brings about protection of cells from toxic effects of components of the Te(r), Phi, and PacB cluster.     

Solubilization of porcine intestinal alpha-glucosidases and evidence for the separate identities of isomaltase and limit dextrinase.

The results of a detailed comparison of the relative efficiencies of different procedures for solubilizing the membrane-bound α-glucosidases in hog intestinal mucosa are reported. Procedures for the selective solubilization of certain members of the complex group of α-glucosidases have been developed. The selective solubilization achieved permits the conclusion that separate α-glucosidases are involved in the hydrolysis of isomaltose and the α-limit dextrins formed from starch by α-amylase.