Potato cyst nematodes Globodera rostochiensis and G. pallida

TaxonomyPhylum Nematoda; class Chromadorea; order Rhabditida; suborder Tylenchina; infraorder Tylenchomorpha; superfamily Tylenchoidea; family Heteroderidae; subfamily Heteroderinae; Genus Globodera.BiologyPotato cyst nematodes (PCN) are biotrophic, sedentary endoparasitic nematodes. Invasive (second) stage juveniles (J2) hatch from eggs in response to the presence of host root exudates and subsequently locate and invade the host. The nematodes induce the formation of a large, multinucleate syncytium in host roots, formed by fusion of up to 300 root cell protoplasts. The nematodes rely on this single syncytium for the nutrients required to develop through a further three moults to the adult male or female stage. This extended period of biotrophy—between 4 and 6 weeks in total—is almost unparalleled in plant–pathogen interactions. Females remain at the root while adult males revert to the vermiform body plan of the J2 and leave the root to locate and fertilize the female nematodes. The female body forms a cyst that contains the next generation of eggs.Host rangeThe host range of PCN is limited to plants of the Solanaceae family. While the most economically important hosts are potato (Solanum tuberosum), tomato (Solanum lycopersicum), and aubergine (Solanum melongena), over 170 species of Solanaceae are thought to be potential hosts for PCN (Sullivan et al., 2007).Disease symptomsSymptoms are similar to those associated with nutrient deficiency, such as stunted growth, yellowing of leaves and reduced yields. This absence of specific symptoms reduces awareness of the disease among growers.Disease controlResistance genes (where available in suitable cultivars), application of nematicides, crop rotation. Great effort is put into reducing the spread of PCN through quarantine measures and use of certified seed stocks.Useful websitesGenomic information for PCN is accessible through WormBase ParaSite.     

Acute toxicity effects of ibuprofen on behaviour and haematological parameters of African catfish Clarias gariepinus (Burchell, 1822)

Indiscriminate discharge of pharmaceutical waste into the aquatic ecosystem may pose serious health challenges to aquatic biota. The effect of acute exposure to ibuprofen was evaluated using changes in behaviour and haematological parameters under static bio-assay method in Clarias gariepinus. Test specimens were exposed to acute concentrations of ibuprofen (0.28, 0.33, 0.38, 0.43 and 0.48 mg l^?1) for 24, 48, 72 and 96 h durations respectively. Behavioural and phenotypic changes were observed in surviving fish. There were significant (p < 0.05) concentration and duration-dependent increases in erythrocyte (RBC), haemoglobin (Hb), pack cell volume (PCV) and leukocytes (WBC) in treated fish compared to the control. Insignificant decreases (p > 0.05) in mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were observed in treated fish compared to the control. Ibuprofen elicited dose and duration- dependent decrease in neutrophil counts with the decreases being significant (p < 0.05) in the higher doses of 0.43 and 0.48 mg l^?1. Ibuprofen did not elicit any significant changes in monocytes, basophils and eosinophils. Changes observed in this study showed that ibuprofen negatively affected the health of the fish and we recommend that discharge of ibuprofen into the aquatic environment should be monitored and controlled.     

Context-dependent memory: colour versus odour

An olfactory stimulus and a visual stimulus were employed in a context- dependent memory study using a prose passage as the to-be-remembered item. Ninety-five university students (aged 17-35 years) learned the passage of prose in the presence of one of the stimuli and were then asked to recall the passage with the original context either reinstated or not reinstated. The results revealed a significant context-dependent memory effect for the olfactory cue but not for the visual cue. They demonstrate support for the effectiveness of odours as context cues and it is suggested that context-dependent memory processes may underlie the formation and retrieval of odour-evoked autobiographical memories.      

Derepression Kinetics of Ornithine Transcarbamylase in Escherichia coli

A mathematical model for the derepression of ornithine transcarbamylase (OTC) in Escherichia coli strain W was derived from a set of 14 assumptions concerning the arginine regulon. The model assumes that active repressor for the arginine regulon is unstable and is only formed when the level of arginyl-tRNA is in excess of the level necessary to maintain protein synthesis for a given cell doubling time. The presence of active repressor was assumed to inhibit the synthesis of messenger RNA coding for the synthesis of the enzymes of the arginine biosynthetic pathway. Numerical estimates of the model's parameters were made and, by simulation on a digital computer, the model was shown to fit kinetic data for derepression of OTC in E. coli W cells in minimal medium growing in flask culture with a doubling time of 60 min and growing in a chemostat with a generation time of 460 min for an assumed OTC-specific mRNA half-life (t_1/2) of 9 min. The model was also shown to predict the increase in the size of bursts of OTC synthesis elicited by addition of arginine to cultures of derepressing E. coli cells with the increase in the delay time before arginine addition. Approximate analytical solutions to the model were obtained for the early phase of derepression and for repression of OTC. These were used to derive graphical methods for determining t_1/2 from repression and derepression transient changes in the OTC level.     

Minicells of Bacillus subtilis

After nitrosoguanidine (N-methyl-N'-nitro-N-nitrosoguanidine) mutagenesis, two Bacillus subtilis mutants (div IV-A1 and div IV-B1) were isolated that are defective in the location of division site along cell length. Both mutations were transferred into strain CU403 by transformation, and their properties were studied in the CU403 genetic background. Location of divisions in close proximity to cell pole regions in both mutants results in minicell production. Purified minicells contain a ratio of ribonucleic acid to protein comparable to that found in the parent cells. Autoradiographs of (3)H-thymine incorporation into deoxyribonucleic acid (DNA), thymine-2-(14)C incorporation into DNA, electron micrographs, and chemical analyses for DNA all fail to demonstrate DNA in the minicells. Minicells produced by both mutants are highly motile, an indication of functional energy metabolism. Electron micrographs reveal that minicells are produced by a structurally normal division mechanism and that minicells contain a normal cell surface. The div IV-A1 mutation has been mapped by PBS1 transduction linked to ura. The div IV-B1 mutation is closely linked to pheA by both PBS1 transduction and by co-transformation.