Trypanosoma cruzi: Flow Cytometric Analysis. I. Analysis of Total DNA/Organism by Means of Mithramycin-Induced Fluorescence1,2

ABSTRACT. Total DNA/organism was determined by flow cytometry on stocks of 33 single-cell-isolate clones and one strain of mithramycin-stained Trypanosoma cruzi. Interstrain differences in mean total DNA/group of 34% and interclone differences in total DNA/organism of 41% were found. Microspectrofluorometric analyses of the trypomastigote stage of selected clones confirmed the flow cytometry data and indicated that the total DNA/organism differences were due to differences in DNA of both the nucleus and kinetoplast with the nucleus being the major contributing factor. These data imply that the potential for genetic diversity in T. cruzi may be very large.     

Type‐II histone deacetylases: elusive plant nuclear signal transducers

Since the beginning of the 21st century, numerous studies have concluded that the plant cell nucleus is one of the cellular compartments that define the specificity of the cellular response to an external stimulus or to a specific developmental stage. To that purpose, the nucleus contains all the enzymatic machinery required to carry out a wide variety of nuclear protein post‐translational modifications (PTMs), which play an important role in signal transduction pathways leading to the modulation of specific sets of genes. PTMs include protein (de)acetylation which is controlled by the antagonistic activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Regarding protein deacetylation, plants are of particular interest: in addition to the RPD3‐HDA1 and Sir2 HDAC families that they share with other eukaryotic organisms, plants have developed a specific family called type‐II HDACs (HD2s). Interestingly, these HD2s are well conserved in plants and control fundamental biological processes such as seed germination, flowering or the response to pathogens. The aim of this review was to summarize current knowledge regarding this fascinating, but still poorly understood nuclear protein family.     

Low levels of ribosomal RNA partly account for the very high photosynthetic phosphorus‐use efficiency of Proteaceae species

Proteaceae species in south‐western Australia occur on phosphorus‐ (P) impoverished soils. Their leaves contain very low P levels, but have relatively high rates of photosynthesis. We measured ribosomal RNA (rRNA) abundance, soluble protein, activities of several enzymes and glucose 6‐phosphate (Glc6P) levels in expanding and mature leaves of six Proteaceae species in their natural habitat. The results were compared with those for Arabidopsis thaliana. Compared with A. thaliana, immature leaves of Proteaceae species contained very low levels of rRNA, especially plastidic rRNA. Proteaceae species showed slow development of the photosynthetic apparatus (‘delayed greening’), with young leaves having very low levels of chlorophyll and Calvin–Benson cycle enzymes. In mature leaves, soluble protein and Calvin–Benson cycle enzyme activities were low, but Glc6P levels were similar to those in A. thaliana. We propose that low ribosome abundance contributes to the high P efficiency of these Proteaceae species in three ways: (1) less P is invested in ribosomes; (2) the rate of growth and, hence, demand for P is low; and (3) the especially low plastidic ribosome abundance in young leaves delays formation of the photosynthetic machinery, spreading investment of P in rRNA. Although Calvin–Benson cycle enzyme activities are low, Glc6P levels are maintained, allowing their effective use.     

Trypanosoma cruzi: Biological Characterization of 19 Clones Derived from Two Chronic Chagasic Patients. I. Growth Kinetics in Liquid Medium1

Nineteen clones of Trypanosoma cruzi were obtained as single-cell isolates from Triatoma infestans. Ten of the clones were isolates from a patient with chronic Chagas' disease; nine clones were isolates from a dog infected with T. cruzi strain CA-I isolated originally from a chronic chagasic patient. The growth kinetics and peak modal Coulter volume of these clones were characterized. Significant inter- and intra-group differences between growth rates and peak modal volumes were found. These data indicate that subpopulations and, consequently, genetic heterogeneity of T. cruzi exist in chronic chagasic patients. All of the clones infected vertebrate cells in vitro.     

The plagiosaurid temnospondyl Plagiosuchus pustuliferus (Amphibia: Temnospondyli) from the Middle Triassic of Germany: anatomy and functional morphology of the skull

The cranial anatomy of the plagiosaurid temnospondyl Plagiosuchus pustuliferus, from the Middle Triassic of Germany, is described in detail on the basis of a newly discovered skull and mandibular material. The highly derived skull is characterized by huge orbitotemporal fenestrae, a reduction of the circumorbital bones – the prefrontal, postfrontal and (probably) postorbital are lost – and the expansion of the jugal to occupy most of the lateral skull margin. Ventrally the extremely long subtemporal vacuities correlate with the elongate adductor fossa of the mandible. The dentition is feebly developed on both skull and mandible. Ossified ?ceratobranchials and ‘branchial denticles’ indicate the presence of open gills clefts in life. The remarkably divergent cranial morphology of P. pustuliferus highlights the extraordinary cranial diversity within the Plagiosauridae, probably unsurpassed within the Temnospondyli. Specific structural aspects of the skull – including an extremely short marginal tooth row, feeble dentition and an elongated chamber for adductor musculature – together with evidence for a hyobranchial skeleton, suggests that P. pustuliferus utilized directed suction feeding for prey capture. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 348–373.