Radish plant behaviour under short-term elevated ozone fumigation

Effects of short-term ozone (O₃) fumigation on radish (Raphanus sativus L.) plants were examined in growth chambers under controlled environment conditions. Plants were exposed to 0 μg/m³ (reference), 80 μg/m³, 160 μg/m³ and 240 μg/m³ O₃ concentrations for 7 h per day for five days. Day/night temperature was 21°C/14°C and photoperiod 16 h. Chlorophyll content was evaluated spectrophotometrically. Chromatographic analysis of saccharides was also undertaken. The results showed that elevated O₃ inhibited the growth of radish rhizocarps, net assimilation rate and biomass accumulation. O₃ induced leaf desiccation, necrosis and premature senescence, but a typical reaction of plants to O₃ stress was the rapid regeneration of new leaves. O₃ inhibited accumulation of carotenoids more than chlorophylls. The higher photosynthetic pigment content in newly generated radish leaves may be regarded as an adaptation of the photosynthetic system to O₃. Leaf saccharide metabolism and incorporation depended on O₃ concentration. Rapid regeneration of new leaves and increased content of photosynthetic pigments is the typical reaction of radish plants to O₃ stress.     

Interfering effects of multitasking on muscle activity in the upper extremity.

Multitasking, where workers are required to perform multiple physical tasks with various levels of cognitive load is common in today's workplace. Simultaneous physical and mental demands are thought to cause task interference and likely increase muscle activity. To test the interfering effects of multitasking, 16 healthy participants performed hand and shoulder exertions with combinations of four grip conditions (no grip, 30% grip with low precision, 30% grip with high precision, and maximal grip) and three shoulder conditions at 90 degrees abduction (maintaining posture, 40% force-controlled moment, 40% posture-controlled moment), with and without the Stroop test while surface EMG was recorded from eight upper extremity muscles. Both 40% MVC shoulder moments increased extrinsic forearm muscle activity by 2-4% MVE (p<0.01). Grip exertion at 30% MVC reduced anterior and middle deltoid activity by 2% MVE (p<0.01). Exerting a constant force against the transducer (force-controlled) required 3-4% MVE greater middle and posterior deltoid activity (p<0.001) compared to supporting an equivalent inertial load at the same shoulder angle (posture-controlled). Performing the mental task (Stroop test) concurrently with either 40% MVC shoulder moments significantly increased trapezius activity by nearly 2% MVE (p<0.05). Interestingly, the Stroop test also reduced all deltoid activity by 1% MVE (p<0.05). The addition of both the Stroop test and force-control shoulder exertion independently reduced maximal grip force by 7% and 10% MVC, respectively. These results suggest that more complex workplace tasks may act to increase muscle load or interfere with task performance. These small but significant findings may play a role in the development of long-term musculoskeletal disorders in the workplace.     

Photorhabdus: towards a functional genomic analysis of a symbiont and pathogen

Pathogenicity and symbiosis are central to bacteria-host interactions. Although several human pathogens have been subjected to functional genomic analysis, we still understand little about bacteria-invertebrate interactions despite their ecological prevalence. Advances in our knowledge of this area are often hindered by the difficulty of isolating and working with invertebrate pathogenic bacteria and their hosts. Here we review studies on pathogenicity and symbiosis in an insect pathogenic bacterium Photorhabdus and its entomopathogenic nematode vector and model insect hosts. Whilst switching between these hosts, Photorhabdus changes from a state of symbiosis with its nematode vector to one of pathogenicity towards its new insect host and both the bacteria and the nematode then cooperatively exploit the dying insect. We examine candidate genes involved in symbiosis and pathogenicity, their secretion and expression patterns in culture and in the host, and begin to dissect the extent of their genetic coregulation. We describe the presence of several large genomic islands, putatively involved in pathogenicity or symbiosis, within the otherwise Yersinia-like backbone of the Photorhabdus genome. Finally, we examine the emerging comparative genomics of the Photorhabdus group and begin to describe the interrelationship between anti-invertebrate virulence factors and those used against vertebrates.     

Acquired and genetic susceptibility to cervical cancer

Infection with high-risk human papilloma virus (HPV) is a necessary risk factor for the development of cervical cancer (CC). However, there are many factors that contribute to the development of CC. We have been investigating the role of polymorphisms in chemical metabolizing genes and life-style factors in the development of CC between two countries with significantly different prevalence of CC. Our data confirm that infection with high-risk HPV is the most significant risk factor for CC in both Venezuela and US. In Venezuela, having multiple sex partners and early sexual activities are significant risk factors (OR=4.7, 95% CI=1.7-13.1; OR=6.7, 95% CI=2.3-20.1, respectively). On the other hand, cigarette smoking is the significant risk factor for women in the US (OR=6.4, 95% CI=1.8-23.2). Genotype analyses were conducted using specimens from the US population only. The GSTM1 null genotype was associated with a significant 3.4 fold increase in risk (95% CI=1.0-11.8) compared with those who were GSTM1 positive, after adjustment for smoking and HPV infection. Polymorphosis in CYP2E1 and mEH are associated with a non-significant increase in risk. Our study indicates that different acquired and genetic susceptibility factors can make significant contributions to the development of environmental disease such as cervical cancer.     

Doc1 mediates the activity of the anaphase-promoting complex by contributing to substrate recognition

The anaphase-promoting complex (APC) is a multisubunit E3 ubiquitin ligase that targets specific cell cycle-related proteins for degradation, regulating progression from metaphase to anaphase and exit from mitosis. The APC is regulated by binding of the coactivator proteins Cdc20p and Cdh1p, and by phosphorylation. We have developed a purification strategy that allowed us to purify the budding yeast APC to near homogeneity and identify two novel APC-associated proteins, Swm1p and Mnd2p. Using an in vitro ubiquitylation system and a native gel binding assay, we have characterized the properties of wild-type and mutant APC. We show that both the D and KEN boxes contribute to substrate recognition and that coactivator is required for substrate binding. APC lacking Apc9p or Doc1p/Apc10 have impaired E3 ligase activities. However, whereas Apc9p is required for structural stability and the incorporation of Cdc27p into the APC complex, Doc1p/Apc10 plays a specific role in substrate recognition by APC-coactivator complexes. These results imply that Doc1p/Apc10 may play a role to regulate the binding of specific substrates, similar to that of the coactivators.     

Implications for the ubiquitination reaction of the anaphase-promoting complex from the crystal structure of the Doc1/Apc10 subunit

The anaphase-promoting complex (APC) is a multi-subunit E3 protein ubiquitin ligase that is responsible for the metaphase to anaphase transition and the exit from mitosis. One of the subunits of the APC that is required for its ubiquitination activity is Doc1/Apc10, a protein composed of a Doc1 homology domain that has been identified in a number of diverse putative E3 ubiquitin ligases. Here, we present the crystal structure of Saccharomyces cerevisiae Doc1/Apc10 at 2.2A resolution. The Doc1 homology domain forms a beta-sandwich structure that is related in architecture to the galactose-binding domain of galactose oxidase, the coagulation factor C2 domain and a domain of XRCC1. Residues that are invariant amongst Doc1/Apc10 sequences, including a temperature-sensitive mitotic arrest mutant, map to a beta-sheet region of the molecule, whose counterpart in galactose oxidase, the coagulation factor C2 domains and XRCC1, mediate bio-molecular interactions. This finding suggests the identification of the functionally important and conserved region of Doc1/Apc10 and, since invariant residues of Doc1/Apc10 colocalise with conserved residues of other Doc1 homology domains, we propose that the Doc1 homology domains perform common ubiquitination functions in the APC and other E3 ubiquitin ligases.     

Factors contributing to discrepancies in population monitoring studies

A review of the scientific literature on population monitoring studies (on non-accidentally exposed populations) frequently show that many of these studies using similarly exposed populations and the same laboratory techniques do not produce consistent results. To illustrate the problem, a brief review of studies using well validated techniques (chromosome aberrations and hprt gene mutation) to elucidate genotoxic effects of cigarette smoking is presented. Although many factors can contribute to the generation of discrepant results, two obvious factors are small sample sizes and inadequate experimental data. In addition, a new factor on genetic susceptibility should be considered in population studies whenever appropriate. The new factor is based on recent data showing the influence of polymorphic metabolizing genes on response to environmental mutagens towards biological effects and disease outcome. The common ones include the cytochrome P450 and the glutathione S-transferase genes. The inclusion of susceptibility factors in population monitoring may revolutionize the approach for health risk assessment and for environmental regulations.     

Four lines of spermatid development and dimorphic spermatozoa in the sea urchin Anthocidaris crassispina (Echinodermata, Echinoida)

 The process of sperm development in the sea urchin Anthocidaris crassispina was studied by light and electron microscopy. Similar to other echinoids studied, a single flagellum, striated rootlet and nuage-like materials were present in spermatogonia of A. crassispina. Spermatocytes near the diplotene stage showed intracellular localization of the axoneme which appeared to be a retracted flagellum prior to cell division. Fibrous filaments were associated with a proximal centriole in spermatocytes and spermatids and might be involved in movement of the proximal centriole. An acrosomal vesicle was developed and a residual body was formed in spermatids. The special development patterns in A. crassispina attributed to the presence of two patterns of tail development and two patterns of mitochondrial development during spermiogenesis. These four lines of spermiogenesis resulted in the formation of four morphological types of sperm cell, i.e. sperms with: (1) a symmetrical midpiece and posterior tail, (2) an asymmetrical midpiece and posterior tail, (3) a symmetrical midpiece and bent tail and (4) an asymmetrical midpiece and bent tail. Sperm cells with bent tails (type 3+4) were probably still at the late spermatid stage because results of scanning electron microscopy demonstrated gradual detachment and eventual straightening of the bent tail, and their percentage occurrence in the sperm population decreased significantly (P<0.05) towards the spawning season of A. crassispina. Spermatozoa with a symmetrical midpiece were dominant (averaging 70% occurrence in the sperm population) over those with an asymmetrical midpiece. The dimorphic spermatozoa in A. crassispina (types 1, 2) are both considered to be euspermatozoa as their morphology is typical for Echinoida. Accepted: 4 May 1998