Phylogenetic analysis of 70 kD heat shock protein sequences suggests a chimeric origin for the eukaryotic cell nucleus

Background: The evolutionary relationships between archaebacteria, eubacteria and eukaryotic cells are of central importance in biology. The current view is that each of these three groups of organisms constitutes a monophyletic domain, and that eukaryotic cells have evolved from an archaebacterial ancestor. Recent studies on a number of highly conserved protein sequences do not, however, support this view and raise important questions concerning the evolutionary relationships between all extant organisms, particularly regarding the origin of eukaryotic cells.Results We have used sequences of 70 kD heat shock protein (hsp70) — the most conserved protein found to date in all species — to examine the evolutionary relationship between various species. We have obtained two new archaebacterial hsp70 sequences from the species, Thermoplasma acidophilum and Halobacterium cutirubrum. A global comparison of hsp70 sequences, including our two new sequences, shows that all known archaebacterial homologs share a number of sequence signatures with the Gram-positive group of bacteria that are not found in any other prokaryotic or eukaryotic species. In contrast, the eukaryotic homologs are shown to share a number of unique sequence features with the Gram-negative bacteria that are not present in any archaebacteria. Detailed phylogenetic analyses of hsp70 sequences strongly support a specific evolutionary relationship between archaebacteria and Gram-positive bacteria on the one hand, and Gram-negative bacteria and eukaryotes on the other. The phylogenetic analyses also indicate a polyphyletic branching of archaebacteria within the Gram-positive species. The possibility that the observed relationships are due to horizontal gene transfers can be excluded on the basis of sequence characteristics of different groups of homologs.Conclusion Our results do not support the view that archaebacteria constitute a monophyletic domain, but instead suggest a close evolutionary linkage between archaebacteria and Gram-positive bacteria. Furthermore, in contrast to the presently accepted view, eukaryotic hsp70s show a close and specific relationship to those from Gram-negative species. To explain the phylogenies based on different gene sequences, a chimeric model for the origin of the eukaryotic cell nucleus involving fusion between an archaebacterium and a Gram-negative eubacterium is proposed. Several predictions from the chimeric model are discussed.     

Evidence for the role of intracellular glutamine level in the regulation of glutamine uptake in the cyanobacteriumAnabaena 7120

The role of intracellular glutamine concentration in the regulation of¹⁴C-glutamine uptake was studied in a diazotrophic cyanobacteriumAnabaena 7120. The uptake pattern was found to be biphasic, consisting of a rapid first phase lasting up to 60 s followed by a slower second phase. Azaserine, which could not inhibit in vitro and in vivo glutamine synthetase (GS) activity effectively, inhibited the¹⁴C-glutamine uptake. Glutamine uptake was also not significantly affected when glutamate, methylglutamate, aspartate, arginine, lysine, hydroxylysine, ornithine, and GS inhibitor,L-methionine-DL-sulfoximine (MSX) were simultaneously available during uptake assay, suggesting that glutamine uptake takes place via a general amino acid permease which does not, however, transport basic and acidic amino acids. The azaserine-treated cells had increased and decreased levels of glutamine and glutamate, respectively, suggesting that the increased intracellular glutamine level is responsible for the inhibition of¹⁴C-glutamine uptake and provides evidence here for the role of an intracellular glutamine pool in the regulation of¹⁴C-glutamine uptake inAnabaena 7120.     

Production of disease-free encapsulated buds of Zingiber officinale Rosc.

Shoot buds of ginger were successfully encapsulated in 4% sodium alginate gel. Encapsulated buds were germinated in vitro to form roots and shoots. In vitro germination (emergence of sprouts) of encapsulated buds ranged from 16.7% to 81.8% on different media after 5 weeks of incubation. Normal plantlets with an average shoot length of 2.3 cm and 1.7 cm root length were successfully transplanted into unsterilized soil without any hardening process. These plantlets showed no symptoms of ginger yellows disease and the causal fungal pathogen failed to grow out on culture media (used as a diagnostic test).     

A shortened dengue IgM capture ELISA using simultaneous incubation of antigen and peroxidase-labeled monoclonal antibody

A shortened IgM capture ELISA for the detection of dengue IgM antibodies using simultaneous incubation of antigen and peroxidase-labeled monoclonal antibody was described. The shortened two-step assay was compared with the four-step IgM capture ELISA on sera from dengue patients confirmed by the hemagglutination inhibition (HI) test. When paired acute and convalescent sera were tested, the shortened ELISA showed 100% agreement with HI results. It detected dengue IgM antibodies in the acute sera of 66% of patients with a primary dengue infection, 60% of patients with a secondary infection, and 98% of patients with a presumptive secondary infection. When the results of 151 dengue patients were combined, 75% of the acute sera were positive by the shortened IgM capture ELISA.     

Identification and Characterization of a Biodegradative Form of Threonine Dehydratase in Senescing Tomato (Lycopersicon esculentum) Leaf

Threonine dehydratase (TD; EC.4.2.1.16) is a key enzyme involved in the biosynthesis of isoleucine. Inhibition of TD by isoleucine regulates the flow of carbon to isoleucine. We have identified two different forms of TD in tomato (Lycopersicon esculentum) leaves. One form, present predominantly in younger leaves, is inhibited by isoleucine. The other form of TD, present primarily in older leaves, is insensitive to inhibition by isoleucine. Expression of the latter enzyme increases as the leaf ages and the highest enzyme activity is present in the old, chlorotic leaves. The specific activity of the enzyme present in older leaves is much higher than the one present in younger leaves. Both forms can use threonine and serine as substrates. Whereas TD from the older leaves had the same Km (0.25 mM) for both substrates, the enzyme from the young leaves preferred threonine (Km = 0.25 mM) over serine (Km = 1.7 mM). The molecular masses of TD from the young and the old leaves were 370,000 and 200,000 D, respectively. High levels of the isoleucine-insensitive form of threonine dehydratase in the older leaves suggests an important role of threonine dehydratase in nitrogen remobilization in senescing leaves.     

Factors affecting in vitro clonal propagation of Prosopis cineraria

Genotype, age of tree, nature of explant and size (length and diameter), season of explant collection, explant position on medium, plant growth regulators and certain additives (ascorbic and citric acids, adenine sulphate, L-arginine, glutamine and ammonium citrate), incubation conditions, and subculturing period greatly influenced the in vitro clonal propagation of P. cineraria. The maximum number of 10–12 shoots were induced from the nodal shoot segment from pruned thorny adult trees on Murashige and Skoog's (MS) medium containing 0.1 mgl^-1 indole- 3-acetic acid (IAA)+2.5 mgl^-1 benzylaminopurine (BAP)+additives. Higher temperature (31+-2°C) and mixed (fluorescent and incandescent) light of 50 mol m^-2 s^-1 photon flux density for 12 h per day photoperiod favoured shoot induction and subsequent growth. Explants from thornless trees produced 6–8 shoots per explant on MS medium containing 0.1 mgl^-1 IAA+5.0 mgl^-1 BAP + additives. Nodal shoot segments obtained from root and stump sprouts produced multiple shoots. Root segments differentiated into multiple shoots on MS medium containing 0.5 mgl^-1 indolebutyric acid (IBA)+2.5 mgl^-1 BAP.Differentiated shoots multiplied best on MS medium containing 0.1 mgl^-1 naphthalene acetic acid (NAA)+1.0 mgl^-1 BAP + additives. To yield multiple shoots the original explant was transferred 6 times on fresh medium after harvesting the differentiated shoots. Shoots were rooted by pulsing with 100 mgl^-1 IBA for 4 h and then culturing on hormone-free half strength MS medium. Initial dark incubation for 5 days at high temperature (33±2°C) was found essential for root induction from shoots which was 63% within two weeks. The rooted plantlets contained a consistent number of chromosomes (2n=28). It is suggested that the protocol developed could be useful for cloning of mature and tested trees of P. cineraria.     

Chaetomella acutiseta produces chaetomellic acids A and B which are reversible inhibitors of farnesyl-protien transferase

Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella. Correspondence to: R. B. Lingham     

Response of pigeon pea cultivars to water stress

Decrease in soil water potential during vegetative and flowering stages of two cultivars of pipeon pea (Cajanus cajari) caused higher decrease in relative water content in cv. ICPL-151 than in cv. H-77-216. Both cultivars showed partial recovery during rehydration. Cv. H-77-216 also accumulated more proline and carbohydrates during stress and showed better drought tolerance than cv. ICPL-151.