Plant organ abscission and the green island effect caused by gallmidges (Cecidomyiidae) on tropical trees

Plants exhibit a wide array of inert and induced responses in defense against herbivore attack. Among these the abscission of organs has been argued to be a highly effective mechanism, depending, however, on the herbivore’s feeding mode. While consisting of plant tissues, insect induced galls are seen as the extended phenotype of the gall inducer which might circumvent many or most of the plant defenses. There is very little information whether and how far beyond the gall tissue gall inducers might affect plant tissues. A localized impact is likely to leave the abscission of galled organs as a viable defense although at a cost. Here, we report on an instance where the host plant, Neea madeirana (Nyctaginaceae) abscises leaves galled by two species of Bruggmannia (Diptera: Cecidomyiidae), more frequently than ungalled leaves in a rain forest in Amazonia, Brazil. Once on the forest floor the leaves decay quickly, while both gall types show signs of localized maintenance of healthy tissues for a while (the green island effect). However, on the forest floor galls are exposed to a new set of potential natural enemies. Both gall types show a minimum of a five-fold increase in mortality due to pathogens (fungi and bacteria) compared to galls that were retained on the host tree. We discuss the adaptive nature of plant organ abscission as a plant defense against gallers and as a gall inducer adaptive trait. Handling editor: Graham Stone.     

Müller Glia as an Active Compartment Modulating Nervous Activity in the Vertebrate Retina: Neurotransmitters and Trophic Factors

Müller cells represent the main type of glia present in the retina interacting with most, if not all neurons in this tissue. Müller cells have been claimed to function as optic fibers in the retina delivering light to photoreceptors with minimal distortion and low loss [Franze et al (2007) Proc Natl Acad Sci 104:8287–8292]. Most of the mediators found in the brain are also detected in the retinal tissue, and glia cells are active players in the synthesis, release, signaling and uptake of major mediators of synaptic function. Müller glia trophic factors may regulate many different aspects of neuronal circuitry during synaptogenesis, differentiation, neuroprotection and survival of photoreceptors, Retinal Ganglion Cells (RGCs) and other targets in the retina. Here we review the role of several transmitters and trophic factors that participate in the neuron-glia loop in the retina. Special issue article in honor of Dr. Ricardo Tapia.     

Ubiquitination of mammalian Pex5p, the peroxisomal import receptor

Protein translocation across the peroxisomal membrane requires the concerted action of numerous peroxins. One central component of this machinery is Pex5p, the cycling receptor for matrix proteins. Pex5p recognizes newly synthesized proteins in the cytosol and promotes their translocation across the peroxisomal membrane. After this translocation step, Pex5p is recycled back into the cytosol to start a new protein transport cycle. Here, we show that mammalian Pex5p is ubiquitinated at the peroxisomal membrane. Two different types of ubiquitination were detected, one of which is thiol-sensitive, involves Cys(11) of Pex5p, and is necessary for the export of the receptor back into the cytosol. Together with mechanistic data recently described for yeast Pex5p, these findings provide strong evidence for the existence of Pex4p- and Pex22p-like proteins in mammals.     

Synthesis and potent antitumor activity of new arylamino derivatives of nor-beta-lapachone and nor-alpha-lapachone

Several arylamino derivatives of nor-beta-lapachone were synthesized in moderate to high yields and found to show very potent cytotoxicity against six neoplastic cancer cells: SF-295 (central nervous system), HCT-8 (colon), MDAMB-435 (breast), HL-60 (leukaemia), PC-3 (prostate), and B-16 (murine melanoma), with IC(50) below 1 microg/mL. Their cytotoxicities were compared to doxorubicin and with their synthetic precursors, beta-lapachone and nor-beta-lapachone. The activity against a normal murine fibroblast L-929 showed that some of the compounds were selective against cancer cells. The absence of hemolytic activity (EC(50)>200 microg/mL), performed with erythrocyte suspensions, suggests that the cytotoxicity of the compounds was not related to membrane damage of mouse erythrocytes. For comparison purposes, one isomeric compound based on nor-alpha-lapachone was also synthesized and showed lower activity than the related ortho-derivative. The modified arylamino quinones appear as interesting new lead compounds in anti-cancer drug development.     

Actions of PACAP and VIP on melanotrope cells of Xenopus laevis

The neuropeptides, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are implicated in the regulation of gene expression and hormone secretion in mammalian melanotrope cells and a mammalian pro-opiomelanocortin (POMC)-producing tumor cell line, but the physiological relevance of this regulation is elusive. The purpose of the present study was to establish if these peptides affect biosynthetic and secretory processes in a well-established physiological model for endocrine cell functioning, the pituitary melanotrope cells of the amphibian Xenopus laevis, which hormonally control the process of skin color adaptation to background illumination. We show that both PACAP and VIP are capable of stimulating the secretory process of the Xenopus melanotrope cell. As the peptides are equipotent, they may exert their actions via a VPAC receptor. Moreover, PACAP stimulated POMC biosynthesis and POMC gene expression. Strong anti-PACAP immunoreactivity was found in the pituitary pars nervosa (PN), suggesting that this neurohemal organ is a source of neurohormonal PACAP action on the melanotropes in the intermediate pituitary. We propose that the PACAP/VIP family of peptides has a physiological function in regulating Xenopus melanotrope cell activity during the process of skin color adaptation.     

Three new species of Croton (Euphorbiaceae s.s.) from the Brazilian Caatinga

While conducting a floristic inventory of Croton from the Brazilian Caatinga, three new species were discovered. Croton arenosus, Croton glandulosobracteatus, and Croton harleyi are described and illustrated here. Based on morphological characters, Croton glandulosobracteatus is proposed to belong to section Barhamia, and C. arenosus and C. harleyi to section Geiseleria.     

Sex-driven differences in Egyptian mongoose’s (<Emphasis Type="Italic">Herpestes ichneumon</Emphasis>) diet in its northwestern European range

Sexual dimorphism in carnivores can result from, or induce, variations in diet and foraging behaviour between individuals of different sexes. Sex-driven behavioural changes in feeding habits may also result in a reduction in intraspecific competition for resources, avoiding dietary overlap by concentrating on different prey sizes/types. We therefore evaluated the variation in feeding habits of both males and females of an invasive and range expanding southern European carnivore, the Egyptian mongoose (Herpestes ichneumon), through gut content analysis of road or predator-control killed animals. The analysis of 59 gut samples, collected in Portugal, revealed that northwestern populations of mongooses prey mostly upon mammals [especially lagomorphs, percentage of biomass (PB) = 44%], reptiles (PB = 28%) and arthropods (PB = 2% but percentage of occurrence = 35%). However, females seem to focus mainly on reptiles (PB = 51%) and mammals (PB = 38%), whilst males consume mostly mammals (PB = 75%). The results suggest that this variation maybe a result of sexual dimorphism (since some variation is documented in a few Egyptian mongoose’s skull measures, namely condylobasal length and canine diameter), with males shifting their diets to prey from which they can obtain more energy. Females seem to be focused on predating lighter animals, probably females or juveniles, a fact that has important game management implications.     

Role of Glycerol Addition on Xylose-to-Xylitol Bioconversion by Candida guilliermondii

The effect of glycerol on xylose-to-xylitol bioconversion by Candida guilliermondii was evaluated by its addition (0.7 and 6.5 g/l) to semidefined media (xylose as a substrate). The glycerol concentrations were chosen based on the amounts produced during previous studies on xylitol production by C. guilliermondii. Medium without glycerol addition (control) and medium containing glycerol (53 g/l) in substitution to xylose were also evaluated. According to the results, the addition of 0.7 g/l glycerol to the fermentation medium favored not only the yield (Y _P/S = 0.78 g/g) but also the xylitol productivity (Q _P = 1.13 g/l/h). During the xylose-to-xylitol bioconversion, the formation of byproducts (glycerol and ethanol) was observed for all conditions employed. In relation to the cellular growth, glycerol as the only carbon source for C. guilliermondii was better than xylose or xylose and glycerol mixtures, resulting in a maximum cellular concentration (5.34 g/l).