Floral structure and ontogeny in Globba (Zingiberaceae)

We present new comparative morphological and ontogenetic data on flowers and bulbils of Globba (Zingiberaceae) to clarify their homologies. Globba flowers are characteristically Zingiberaceous, possessing a single stamen and epigynous (``supragynopleural') nectaries, but are unusual as the anther bears triangular lateral outgrowths and the style is held tightly in position across the curvature of the filament like a bowstring. Floral ontogeny in Globba is similar to other Zingiberaceae. Characteristic features, such as anther wings, occur late in development, shortly before anthesis. Unusually Globba has zygomorphic style anatomy with only two abaxial vascular bundles, in contrast to most other Zingiberaceae, which possess three stylar traces. The ovary is unilocular and lacks septa. Bulbils have enclosing bracts and replace flowers in the lower part of the inflorescence; they consist of a shoot with an enlarged corky storage root forming the bulk of the propagule.     

Cadmium and copper inhibit both DNA repair activities of polynucleotide kinase

Human exposure to heavy metals is of increasing concern due to their well-documented toxicological and carcinogenic effects and rising environmental levels through industrial processes and pollution. It has been widely reported that such metals can be genotoxic by several modes of action including generation of reactive oxygen species and inhibition of DNA repair. However, although it has been observed that certain heavy metals can inhibit single strand break (SSB) rejoining, the effects of these metals on SSB end-processing enzymes has not previously been investigated. Accordingly, we have investigated the potential inhibition of polynucleotide kinase (PNK)-dependent single strand break repair by six metals: cadmium, cobalt, copper, nickel, lead and zinc. It was found that micromolar concentrations of cadmium and copper are able to inhibit the phosphatase and kinase activities of PNK in both human cell extracts and purified recombinant protein, while the other metals had no effect at the concentrations tested. The inhibition of PNK by environmentally and physiologically relevant concentrations of cadmium and copper suggests a novel means by which these toxic heavy metals may exert their carcinogenic and neurotoxic effects.     

The role of p53 in pigmentation, tanning and melanoma

p53 has a central role in skin pigmentation and may impact on melanoma at all stages, however, as it's mutation frequency in melanoma is low, it's role has been somewhat under-appreciated. During normal skin function, p53 in the keratinocyte is a transducer of the skin tanning signal and an essential component of what is effectively a keratinocyte-melanocyte signaling cycle that regulates skin pigmentation. It is clear that this cycle functions optimally in skin of dark pigmentation. When melanin biosynthesis is genetically disrupted in skin of white complexion, we propose that this cycle operates as a promoter of melanocyte proliferation. The cell autonomous function of p53 in melanocytes is not well described, however, the balance of the evidence suggests that p53 is an effective tumor suppressor and the myriad of mechanisms by which the p53 pathway may be dysregulated in tumors attests to it importance as a tumor suppressor. In this review, we outline the known mechanisms that impair p53 itself and its immediate regulators or target genes during melanomagenesis. Due to the importance of this pathway, it is clear that p53 disruptions may relate directly to a patient's prognosis. This pathway will continue to be a focus of investigation, particularly with respect to targeted experimental chemotherapeutics.     

Options for reducing the negative effects of nitrogen in agriculture

After addition to farms by fertilizer, crop residues, biological fixation and animal excreta, nitrogen can be lost through gaseous emission, runoff and leaching to contaminate the atmosphere and water bodies, and cause adverse health effects. The efficiency of fertilizer nitrogen can be increased and losses reduced, by matching supply with crop demand, optimizing split application schemes, changing the form to suit the conditions, and use of slow-release fertilizers and inhibitors. In addition, agronomic practices such as higher plant densities, weed and pest control and balanced fertilization with other nutrients can also increase efficiency of nitrogen use. Efficiency of use by animals can be increased by diet manipulation. Feeding dairy cattle low degradable protein and high starch diets, and grazing sheep and cattle on grasses high in water soluble carbohydrate result in less nitrogen excretion in urine and reduced ammonia volatilization.     

Human pigmentation genes: identification, structure and consequences of polymorphic variation

The synthesis of the visible pigment melanin by the melanocyte cell is the basis of the human pigmentary system, those genes directing the formation, transport and distribution of the specialised melanosome organelle in which melanin accumulates can legitimately be called pigmentation genes. The genes involved in this process have been identified through comparative genomic studies of mouse coat colour mutations and by the molecular characterisation of human hypopigmentary genetic diseases such as OCA1 and OCA2. The melanocyte responds to the peptide hormones alpha-MSH or ACTH through the MC1R G-protein coupled receptor to stimulate melanin production through induced maturation or switching of melanin type. The pheomelanosome, containing the key enzyme of the pathway tyrosinase, produces light red/yellowish melanin, whereas the eumelanosome produces darker melanins via induction of additional TYRP1, TYRP2, SILV enzymes, and the P-protein. Intramelanosomal pH governed by the P-protein may act as a critical determinant of tyrosinase enzyme activity to control the initial step in melanin synthesis or TYRP complex formation to facilitate melanogenesis and melanosomal maturation. The search for genetic variation in these candidate human pigmentation genes in various human populations has revealed high levels of polymorphism in the MC1R locus, with over 30 variant alleles so far identified. Functional correlation of MC1R alleles with skin and hair colour provides evidence that this receptor molecule is a principle component underlying normal human pigment variation.     

Free radical-induced double lesions in DNA

This review surveys the work that has been done on free radical-induced DNA double lesions. Double lesions consist of two modifications of the DNA in close proximity. Double lesions can be generated by a single free radical-initiating event and the mechanism of formation often involves the participation of guanine. The identification of double lesions in oligomer and polymer DNA is reviewed and possible mechanisms of formation are outlined. The potential biological significance of double lesions is discussed. Double lesions induced by UV light are outside the scope of this review.     

Sex differences in common Marmosets (<Emphasis Type="Italic">Callithrix jacchus</Emphasis>) in response to an unfamiliar food task

There is a growing body of information on sex differences in callitrichid behaviour that includes the animals performance in food tasks. For example, both reproductive and non-reproductive adult females have been found to be more successful than adult males in solving food tasks. In this study ten adult male and ten adult female common marmosets (Callithrix jacchus), housed individually, were tested with an unfamiliar task that involved the extraction of an embedded food. The task was to open a plastic canister that contained a raisin; the open end was covered with parchment paper. Each marmoset was given 15 trials in three blocks of 5 consecutive days. We measured the latency for each animal to open the lid and get the raisin—by one of five strategies that spontaneously emerged. The females learned the task faster and more efficiently than males; all the females opened the canister on day 1, for instance, in contrast to seven of the males on the same day. Females also progressively decreased the time that they took to open the tube. The final latency on day 15, for instance, was significantly shorter for the females. These results are consistent with relevant literature for callitrichids and cannot be accounted for in terms of differences in mental abilities, strength, hand morphology, or energy requirements. Further investigation is necessary to clarify the reasons for these differences.     

Genetic locus and structural characterization of the biochemical defect in the O-antigenic polysaccharide of the symbiotically deficient Rhizobium etli mutant, CE166. Replacement of N-acetylquinovosamine with its hexosyl-4-ulose precursor

The O-antigen polysaccharide (OPS) of Rhizobium etli CE3 lipopolysaccharide (LPS) is linked to the core oligosaccharide via an N-acetylquinovosaminosyl (QuiNAc) residue. A mutant of CE3, CE166, produces LPS with reduced amounts of OPS, and a suppressed mutant, CE166 alpha, produces LPS with nearly normal OPS levels. Both mutants are deficient in QuiNAc production. Characterization of OPS from CE166 and CE166 alpha showed that QuiNAc was replaced by its 4-keto derivative, 2-acetamido-2,6-dideoxyhexosyl-4-ulose. The identity of this residue was determined by NMR and mass spectrometry, and by gas chromatography-mass spectrometry analysis of its 2-acetamido-4-deutero-2,6-dideoxyhexosyl derivatives produced by reduction of the 4-keto group using borodeuteride. Mass spectrometric and methylation analyses showed that the 2-acetamido-2,6-dideoxyhexosyl-4-ulosyl residue was 3-linked and attached to the core-region external Kdo III residue of the LPS, the same position as that of QuiNAc in the CE3 LPS. DNA sequencing revealed that the transposon insertion in strain CE166 was located in an open reading frame whose predicted translation product, LpsQ, falls within a large family of predicted open reading frames, which includes biochemically characterized members that are sugar epimerases and/or reductases. A hypothesis to be tested in future work is that lpsQ encodes UDP-2-acetamido-2,6-dideoxyhexosyl-4-ulose reductase, the second step in the synthesis of UDP-QuiNAc from UDP-GlcNAc.     

An overall perspective of X-ray damage to a DNA oligomer mediated by reactive oxygen species

The products produced by X irradiation of an oxygenated aqueous solution containing d(CpApTpG) were analyzed by NMR spectroscopy and mass spectrometry. Thirteen different base modifications were detected, including a novel product formed by the addition of oxygen to guanine. Seven different strand break products were identified, including strands having 5'-phosphoryl groups, 3'-phosphoryl groups and groups having 3'-phosphoglycolates as termini. The products produced in largest yield contained base modifications: Pyrimidine bases degraded to a formamido moiety, the 8-oxo-7,8-dihydroguanine (8-oxoguanine) lesion, and double base lesions in which both the 8-oxo-7,8-dihydroguanine lesion and a formamido remnant are present.