Influence of medium composition on callus induction and camptothecin(s) accumulation in Nothapodytes foetida

Camptothecin(s) production was examined in callus cultures derived from cotyledons of Nothapodytes foetida (Weigh) Sleumer. The calluses were grown on various combinations of Murashige and Skoog's basal media supplemented with auxins 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), a-napthalene acetic acid (NAA) and indole-3-acetic acid (IAA) with 6-benzyl aminopurine (BA)/kinetin in different concentrations. The presence of camptothecin (CPT) and 9-methoxycamptothecin (9-OMeCPT) were analyzed by HPLC in relation to the media composition. Hyper production of CPT(1.306% on dry wt. basis) was observed with a combination of 2,4-D with BA and 2,4,5-T and NAA in 1-month-old callus.     

Recent developments in mesophyll conductance in C3, C4, and crassulacean acid metabolism plants

The conductance of carbon dioxide (CO₂) from the substomatal cavities to the initial sites of CO₂ fixation (g_m) can significantly reduce the availability of CO₂ for photosynthesis. There have been many recent reviews on: (i) the importance of g_m for accurately modelling net rates of CO₂ assimilation, (ii) on how leaf biochemical and anatomical factors influence g_m, (iii) the technical limitation of estimating g_m, which cannot be directly measured, and (iv) how g_m responds to long‐ and short‐term changes in growth and measurement environmental conditions. Therefore, this review will highlight these previous publications but will attempt not to repeat what has already been published. We will instead initially focus on the recent developments on the two‐resistance model of g_m that describe the potential of photorespiratory and respiratory CO₂ released within the mitochondria to diffuse directly into both the chloroplast and the cytosol. Subsequently, we summarize recent developments in the three‐dimensional (3‐D) reaction‐diffusion models and 3‐D image analysis that are providing new insights into how the complex structure and organization of the leaf influences g_m. Finally, because most of the reviews and literature on g_m have traditionally focused on C₃ plants we review in the final sections some of the recent developments, current understanding and measurement techniques of g_m in C₄ and crassulacean acid metabolism (CAM) plants. These plants have both specialized leaf anatomy and either a spatially or temporally separated CO₂ concentrating mechanisms (C₄ and CAM, respectively) that influence how we interpret and estimate g_m compared with a C₃ plants.     

Utilization of acidic amino acids and their amides by pseudomonads: role of periplasmic glutaminase-asparaginase

The acidic amino acids (Asp, Glu) and their amides (Asn, Gln) support rapid growth of a variety of Pseudomonas strains when provided as the sole source of carbon and nitrogen. All key enzymes of glutamate metabolism were detected in P. fluorescence, with glutaminase and asparaginase showing the highest specific activities. A periplasmic glutaminase/asparaginase activity (PGA) was found in all pseudomonads examined, including a number of root-colonizing biocontrol strains. The enzyme was purified and shown to be identical with the ansB gene product described previously. In addition to PGA, P. fluorescens contains a cytoplasmic asparaginase with marked specificity for Asn. PGA is strongly and specifically induced by its substrates (Asn, Gln) but also by the reaction products (Asp, Glu). In addition, PGA is subject to efficient carbon catabolite repression by glucose and by citrate cycle metabolites. A mutant of P. putida KT2440 with a disrupted ansB gene was unable to utilize Gln, whereas growth of the mutant on other amino acids was normal.     

Isolation and characterization of halotolerant Streptomyces radiopugnans from Antarctica soil

An actinomycete wild strain PM0626271 (= MTCC 5447), producing novel antibacterial compounds, was isolated from soil collected from Antarctica. The taxonomic status of the isolate was established by polyphasic approach. Scanning electron microscopy observations and the presence of LL‐Diaminopimelic acid in the cell wall hydrolysate confirmed the genus Streptomyces. Analysis of 16S rRNA gene sequence showed highest sequence similarity to Streptomyces radiopugnans (99%). The phylogenetic tree constructed using near complete 16S rRNA gene sequences of the isolate and closely related strains revealed that although the isolate fell within the S. radiopugnans gene subclade, it was allocated a different branch in the phylogenetic tree, separating it from the majority of the radiopugnans strains. Similar to type strain, S. radiopugnans R97^T, the Antarctica isolate displayed thermo tolerance as well as resistance to ⁶⁰Co gamma radiation, up to the dose of 15 kGy. However, media and salt tolerance studies revealed that, unlike the type strain, this isolate needed higher salinity for its growth. This is the first report of S. radiopugnans isolated from the Antarctica region. The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of Streptomyces radiopugnans MTCC 5447 is JQ723477 .

Significance and Impact of the Study

The study presents the first report of isolation of Streptomyces radiopugnans from Antarctica. To date, there is only one publication regarding S. radiopugnans R97^T isolated from radiation‐polluted soil. Like the type strain, Antarctica isolate was thermotolerant and radiotolerant, but in addition, it required salts for growth and did not degrade phenol. We envisaged that metabolic pattern of the same species varies based on acclimatization in its native ecological habitat. Additionally, Antarctica isolate had produced novel antibacterial compounds (patent‐US2012/0156295). The study highlighted that least explored extreme regions like Antarctica are rich resources of novel microbial strains producing novel bioactive compounds.     

Polymorphism in the DNA repair enzyme XRCC1: utility of current database and implications for human health risk assessment

Genetic polymorphisms are increasingly recognized as sources of variability not only in toxicokinetic but also in toxicodynamic response to environmental agents. XRCC1 is involved in base excision repair (BER) of DNA; it has variant genotypes that are associated with modified repair function. This analysis focuses on four polymorphisms: three in the coding region that affect protein structure and one in an upstream regulatory sequence that affects gene expression. The Arg399Gln variant is the most widely studied with evidence supporting a quantitative effect of genotype on phenotype. The homozygous variant (Gln/Gln) can have 3-4-fold diminished capacity to remove DNA adducts and oxidized DNA damage. This variant is relatively common in Caucasians and Asians where approximately 10% are homozygous variant. In contrast, the Arg194Trp variant appears to protect against genotoxic effects although the degree to which DNA repair is enhanced by this polymorphism is uncertain. The homozygous variant is rare in Caucasians and African Americans but it is present at 7% in Asians. A third coding region polymorphism at codon 280 appears to decrease repair function but additional quantitative information is needed and the homozygous variant is rare across populations studied. A polymorphism in an upstream promoter binding sequence (-77T>C) appears to lower XRCC1 levels by decreasing gene expression. Based upon genotype effect on phenotype and allele frequency, the current analysis finds that the codon 399 and upstream (-77) polymorphisms have the greatest potential to affect the toxicodynamic response to DNA damaging agents. However, the implications for risk assessment are limited by the likelihood that polymorphisms in multiple BER genes interact to modulate DNA repair.     

Changes in mouse brain diazepam receptor binding after phenobarbital administration

Specific ³H-diazepam binding was measured $\text{in vitro}$ in adult mouse (strain, Crl=CD-1) brain after four days of an inductive dose of phenobarbital pretreatment (i.p.). Sexual dimorphism was observed in ³H-diazepam brain binding, female mice had significantly higher benzodiazepine binding than males without any differences in apparent affinity constants (K_D). Phenobarbital pretreatment caused a significant decrease in the maximal number of binding sites (Bmax) as well as in dissociation rate constants in both sexes.     

Heterogeneity across the dorso-ventral axis in zebrafish EVL is regulated by a novel module consisting of sox, snail1a and max genes

In vertebrates, the dorso-ventral (DV) axis is defined by the combinatorial action of localised Wnt, FGF and Nodal signalling along with the antagonizing activities of Chordin and BMP pathways. Our knowledge of the factors that may act in concert with these core pathways to regulate early embryonic patterning is far from complete. Furthermore, while all three germ layers respond to these patterning cues, it is not clear whether in zebrafish the outermost protective epithelium, the enveloping layer (EVL), is also patterned along the DV axis. Here, we have identified a transgenic line driving GFP under a crestin promoter, which specifically labels the dorsal domain of the EVL suggesting heterogeneity in the EVL across the DV axis. Our attempts to understand how the expression from this promoter fragment is regulated specifically in the dorsal domain, have unravelled potential novel players involved in early EVL and embryonic patterning. We show that along with Nodal signalling components, four proteins Sox11b, Sox19b, Snail1a and Max are involved in regulating the size of this EVL domain. However, Chordin-BMP signalling might be dispensable for the dorso-ventral patterning of the EVL. For the first time, this transgenic line unravels the heterogeneity in the EVL and will serve as an important tool in understanding the molecular basis of the DV patterning of the EVL.