http://hdl.handle.net/10453/164 2013-06-19T16:46:30Z http://hdl.handle.net/10453/18038 Isoforms Of The Heteropteran Nezara Viridula Ecdysone Receptor: Protein Characterisation, Rh5992 Insecticide Binding And Homology Modelling Tohidi-Esfahani Donya; Lawrence M.C.; Graham Lloyd; Hannan G; Simpson Ann; Hill Ron Abstract: BACKGROUND: Certain bisacylhydrazine compounds such as tebufenozide (RH5992) have been shown to act as order-specific insecticides. Their compatibility with predatory Heteroptera, which are used as biological control agents, has also been demonstrated. However, the molecular mode of action of these ecdysone agonists has not been explored in a heteropteran, much less one that is a significant agricultural pest, such as Nezara viridula. RESULTS: Alternatively spliced ligand-binding regions of the N. viridula ecdysone receptor were expressed, purified and characterised by 2D gel analysis, mass spectrometry, homology modelling and competitive binding of a bisacylhydrazine insecticidal compound (RH5992) and various ecdysteroids. Ligand binding by the two splice isoforms was indistinguishable, and relative affinities were found to occur in the order muristerone A > ponasterone A > 20-hydroxyecdysone > inokosterone > RH5992 > alpha-ecdysone. CONCLUSION: The predicted difference in amino acid sequence between the ligand-binding domains of the N. viridula ecdysone receptor splice variants was verified by mass spectrometry. Both splice variant isoforms exhibit a greater affinity for the bisacylhydrazine insecticide RH5992 than do the other hemipteran ecdysone receptors characterised to date. Their affinities for a range of ecdysteroids also distinguish them from the ecdysone receptors of other Hemiptera characterised thus far. Homology models of both N. viridula receptor isoforms provide further insight into the bisacylhydrazine- and ecdysteroid-binding properties of these receptors, including their similar affinity for 20-hydroxyecdysone and the postulated pentatomomorphan moulting hormonemakisterone A. 2011-01-01T00:00:00Z http://hdl.handle.net/10453/18039 A Negative Feedback Loop That Limits The Ectopic Activation Of A Cell Type-specific Sporulation Sigma Factor Of Bacillus Subtilis Serrano M.; Real G.; Da Silva Santos Joana; Carneiro J.; Moran C.P.; Henriques A.O. Two highly similar RNA polymerase sigma subunits, sigma(F) and sigma(G), govern the early and late phases of forespore-specific gene expression during spore differentiation in Bacillus subtilis. sigma(F) drives synthesis of sigma(G) but the latter only becomes active once engulfment of the forespore by the mother cell is completed, its levels rising quickly due to a positive feedback loop. The mechanisms that prevent premature or ectopic activation of sigma(G) while discriminating between sigma(F) and sigma(G) in the forespore are not fully comprehended. Here, we report that the substitution of an asparagine by a glutamic acid at position 45 of sigma(G) (N45E) strongly reduced binding by a previously characterized anti-sigma factor, CsfB (also known as Gin), in vitro, and increased the activity of sigma(G) in vivo. The N45E mutation caused the appearance of a sub-population of pre-divisional cells with strong activity of sigma(G). CsfB is normally produced in the forespore, under sigma(F) control, but sigGN45E mutant cells also expressed csfB and did so in a sigma(G) -dependent manner, autonomously from sigma(F). Thus, a negative feedback loop involving CsfB counteracts the positive feedback loop resulting from ectopic sigma(G) activity. N45 is invariant in the homologous position of sigma(G) orthologues, whereas its functional equivalent in sigma(F) proteins, E39, is highly conserved. While CsfB does not bind to wildtype sigma(F), a E39N substitution in sigma(F) resulted in efficient binding of CsfB to sigma(F). Moreover, under certain conditions, the E39N alteration strongly restrains the activity of sigma(F) in vivo, in a csfB-dependent manner, and the efficiency of sporulation. Therefore, a single amino residue, N45/E39, is sufficient for the ability of CsfB to discriminate between the two forespore-specific sigma factors in B. subtilis. 2011-01-01T00:00:00Z http://hdl.handle.net/10453/18041 Phytotoxicity of arsenate and salinity on early seedling growth of rice (Oryza sativa L.): A threat to sustainable rice cultivation in South and South-East Asia Rahman Mohammad; Rahman Mohammad; Maki Teruya; Hasegawa Hiroshi Arsenic (As) contamination is an important environmental consequence in some parts of salinity-affected South (S) and South-East (SE) Asia. In this study, we investigated the individual and combined phytotoxicity of arsenic (As) [arsenate; As(V)] and salinity (NaCl) on early seedling growth (ESG) of saline-tolerant and non-tolerant rice varieties. Germination percentage (GP), germination speed (GS) and vigor index (VI) of both saline-tolerant and non-tolerant rice varieties decreased significantly (p[0.01) with increasing As(V) and NaCl concentrations. The highest GP(91%) was observed for saline non-tolerant BRRI dhan28 and BRRI dhan49, while the lowest (62%) was for salinetolerant BRRI dhan47. The ESG parameters, such as weights and relative lengths of plumule and radicle, also decreased significantly (p\0.01) with increasing As(V) and NaCl concentrations. Relative radicle length was more affected than plumule length by As(V) and NaCl. Although VI of saline-tolerant and non-tolerant rice seedlings showed significant variation (p\0.05), weights and lengths of plumule and radicle of different rice varieties did not show significant variation for As(V) and NaCl treatments. Results reveal that the combined phytotoxicity of As(V) and NaCl on rice seed germination and ESG are greater than their individual toxicities, and some saline-tolerant rice varieties are more resistant to the combined phytotoxicity of As(V) and NaCl than the saline non-tolerant varieties. 2012-01-01T00:00:00Z http://hdl.handle.net/10453/18040 Effects Of Crystallinity And Chemical Variation On Apparent Band-gap Shift In Polycrystalline Indium Nitride Chen P.P.-T.; Downes J.E.; Fernandes A.J.; Butcher K.S.A.; Wintrebert-Fouquet M.; Wuhrer Richard; Phillips Matthew The nature of the apparent band-gap shift in polycrystalline indium nitride thin-films, grown by remote-plasma-enhanced chemical vapour deposition at 535 +/- 10 degrees C. has been investigated separately in relation to growth temperature dependent crystallinity and chemical variation. Substrates of sapphire and gallium nitride on sapphire were used to study the effect of a stress-reduced template on indium nitride crystallite quality and apparent band-gap. To mimic surface growth temperature variations two glass substrates of differing thickness and thermal conductivity were intentionally used for the same growth conditions. The samples were characterised using optical transmission, scanning electron microscope, X-ray diffraction, and high-resolution X-ray photoelectron spectroscopy. The results indicate that the apparent band-gap shift in polycrystalline narrow band-gap indium nitride thin-films is not primarily determined by the quality of indium nitride crystallites but rather it is associated with growth temperature dependent chemical variations in the films 2011-01-01T00:00:00Z