<i>In vitro</i> evaluation of antifungal activity of Agave (<i>Agave scabra</i>, Salm Dyck) extracts against post-harvest mushrooms

The agricultural sector, and particularly the horticultural production, has a singular importance in agriculture, considering that it ranks second on agricultural products, nationally and worldwide. Fungal diseases are one of the major causes of vegetable loss during storage, reducing their nutritional value, quality and sale price. Vegetables are usually exposed to diverse treatments with chemical products before storage; as a result, fungal populations develop an increased resistance over time becoming more difficult to control. Because of this, research efforts toward finding more suitable chemicals to control fungal diseases are needed. Natural extracts may be an alternative solve this problem. In the present investigation the fungicidal activity of aqueous and ethanol extracts of Agave scabra was evaluated on the growth of Botrytis cinerea, Mucor sp., Aspergillus niger, Fusarium sp. and Penicillium sp., whose strains were isolated from potato and tomato. To assess their effects, the agar-dilution and agar-well techniques were performed. The ethanol extract was more effective against Botrytis cinerea and Mucor sp. when the agar-well method was used. However, when using the agar-dilution method the ethanol extract of Agave scabra inhibited the growth of Botrytis cinerea, Mucor sp. and Penicillium sp.     

The mycoflora and toxicity of feedstuffs from a production plant in córdoba, Argentina

Feedstuffs used for poultry nutrition in Argentina were analyzed for fungal flora and natural incidence of mycotoxins. Survey of 120 samples of poultry feeds, taken from May 1998 to April 1999, showed the presence of 15 genera of filamentous fungi. The predominant genera wereFusarium spp. andPenicillium ssp., isolated in 67.5 % of the samples, followed byAspergillus spp. (57.5 %). Yeast, were significantly isolated from most of the samples. Species identification was carried down for the toxigenic genera. Fungal total counts of poultry feeds ranged from 2.0 × 10³ to 3.0 × 10⁵ CFU g^-1 The fungal total counts during two months of sampling, were slightly over the limit value of 1 × 105 CFU g^-1, which ensure the hygienic quality of the feed. Potentially toxicogenic species presented moderate mean colony counts. Many of the fungi isolated from poultry feeds are mycotoxin producers. Fumonisins had the highest incidence, and were found in 97 % of the analyzed samples followed by aflatoxin B₁ (46 %), zearalenone (18 %) and deoxynivalenol (6 %). On the co-occurrence of both carcinogenic mycotoxins, all of the FBs contaminated feed samples were co-contaminated with AFB₁. The results show the relevance of the samples screening for viable fungi propagules and the surveillance of their associated mycotoxins in poultry feeds.     

Cytoplasmic Dynein Function Is Essential in Drosophila Melanogaster

The microtubule motor cytoplasmic dynein has been implicated in a variety of intracellular transport processes. We previously identified and characterized the Drosophila gene Dhc64C, which encodes a cytoplasmic dynein heavy chain. To investigate the function of the cytoplasmic dynein motor, we initiated a mutational analysis of the Dhc64C dynein gene. A small deletion that removes the chromosomal region containing the heavy chain gene was used to isolate EMS-induced lethal mutations that define at least eight essential genes in the region. Germline transformation with a Dhc64C transgene rescued 16 mutant alleles in the single complementation group that identifies the dynein heavy chain gene. All 16 alleles were hemizygous lethal, which demonstrates that the cytoplasmic dynein heavy chain gene Dhc64C is essential for Drosophila development. Furthermore, our failure to recover somatic clones of cells homozygous for a Dhc64C mutation indicates that cytoplasmic dynein function is required for cell viability in several Drosophila tissues. The intragenic complementation of dynein alleles reveals multiple mutant phenotypes including male and/or female sterility, bristle defects, and defects in eye development.     

Targeted disruption of retinoic acid receptor alpha (RAR alpha) and RAR gamma results in receptor-specific alterations in retinoic acid-mediated differentiation and retinoic acid metabolism.

F9 embryonic teratocarcinoma stem cells differentiate into an epithelial cell type called extraembryonic endoderm when treated with retinoic acid (RA), a derivative of retinol (vitamin A). This differentiation is presumably mediated through the actions of retinoid receptors, the RARs and RXRs. To delineate the functions of each of the different retinoid receptors in this model system, we have generated F9 cell lines in which both copies of either the RAR alpha gene or the RAR gamma gene are disrupted by homologous recombination. The absence of RAR alpha is associated with a reduction in the RA-induced expression of both the CRABP-II and Hoxb-1 (formerly 2.9) genes. The absence of RAR gamma is associated with a loss of the RA-inducible expression of the Hoxa-1 (formerly Hox-1.6), Hoxa-3 (formerly Hox-1.5), laminin B1, collagen IV (alpha 1), GATA-4, and BMP-2 genes. Furthermore, the loss of RAR gamma is associated with a reduction in the metabolism of all-trans-RA to more polar derivatives, while the loss of RAR alpha is associated with an increase in metabolism of RA relative to wild-type F9 cells. Thus, each of these RARs exhibits some specificity with respect to the regulation of differentiation-specific gene expression. These results provide an explanation for the expression of multiple RAR types within one cell type and suggest that each RAR has specific functions.     

Flowering responses to altered expression of phytochrome in mutants and transgenic lines of Arabidopsis thaliana (L.) Heynh.

The long-day plant Arabidopsis thaliana (L.) Heynh. flowers early in response to brief end-of-day (EOD) exposures to far-red light (FR) following a fluorescent short day of 8 h. FR promotion of flowering was nullified by subsequent brief red light (R) EOD exposure, indicating phytochrome involvement. The EOD response to R or FR is a robust measure of phytochrome action. Along with their wild-type (WT) parents, mutants deficient in either phytochrome A or B responded similarly to the EOD treatments. Thus, neither phytochrome A nor B exclusively regulated flowering, although phytochrome B controlled hypocotyl elongation. Perhaps a third phytochrome species is important for the EOD responses of the mutants and/or their flowering is regulated by the amount of the FR-absorbing form of phytochrome, irrespective of the phytochrome species. Overexpression of phytochrome A or phytochrome B resulted in differing photoperiod and EOD responses among the genotypes. The day-neutral overexpressor of phytochrome A had an EOD response similar to all of the mutants and WTs, whereas R EOD exposure promoted flowering in the overexpressor of phytochrome B and FR EOD exposure inhibited this promotion. The comparisons between relative flowering times and leaf numbers at flowering of the over-expressors and their WTs were not consistent across photoperiods and light treatments, although both phytochromes A and B contributed to regulating flowering of the transgenic plants.     

Is the far-red-absorbing form of Avena phytochrome A that is present at the end of the day able to sustain stem-growth inhibition during the night in transgenic tobacco and tomato seedlings?

Avena phytochrome A (phyA) overexpressed in tobacco (Nicotiana tabacum L.) and tomato (Lycopersicon sculentum Mill) was functionally characterised by comparing wild-type (WT) and transgenic seedlings. Different proportions of phytochrome in its far-red-absorbing form (Pfr/P) were provided by end-of-day (EOD) light pulses. Stem-length responses occurred largely in the range of low Pfr/P (3–61%) for WT seedlings and in the range of high Pfr/P (61–87%) for transgenic seedlings. A similar shift was observed when the photoperiod was interrupted by short light pulses providing different Pfr/P ratios and followed by 1 h dark incubation. In other experiments, Avena phyA was allowed to re-accumulate in darkness and subsequently phototransformed to Pfr but no extra inhibition of stem extension growth was observed. In transgenic tomato seedlings the response to EOD far-red light was faster and the response to a far-red light pulse delayed into darkness was larger than in the WT. Avena phyA Pfr remaining at the end of the photoperiod appears intrinsically unable to sustain growth inhibition in subsequent darkness. Avena phyA modifies the sensitivity and the kinetics of EOD responses mediated by native phytochrome.Abbreviations EOD end-of-day - FR far-red light - Pfr/P pro-portion of phytochrome in its FR-absorbing form - phyA phyto-chrome A - phyB phytochrome B - R red light - RFR R to FR ratio - WT wild type We thank Dr Brian Thomas for providing the antibodies used in this work, and Federico Guerendiain for his excellent technical assistance. This work was financially supported by grants UBA AG 040 and Fundacion Antorchas A-12830/1-19 (both to J.J.C.), PID-CONICET (to R.A.S. and J.J.C.), United States Department of Energy DE-FG02-88ER13968 (to R.D.V.).     

Are the phytochromes protein kinases?

Summary The biochemical mechanism of phytochrome action is unknown. We have examined the proposal, based on sequence similarities to the sensor histidine kinase components of bacterial two-component signaling systems, that the phytochromes may be functional homologs of these kinases. Four amino acids, three highly conserved between the phytochrome and bacterial kinase molecules and the other, the histidine residue putatively the target of autophosphorylation, were changed singly in the oat phytochrome A sequence by in vitro site-directed mutagenesis, and the resultant mutant photo-receptor molecules were assayed for activity by overexpression in transgenic Arabidopsis. Three of the four mutant molecules retained activity equivalent to that of the unmutagenized parent sequence, whereas the fourth mutant could not be evaluated because of low expression. The data show that the former three mutagenized residues are not essential for phytochrome A function in transgenic Arabidopsis, but, because of the negative nature of the results, the possibility cannot be precluded that the photoreceptor functions as a protein kinase independent of these residues.Dedicated to Professor Eldon H. Newcomb in recognition of his contributions to cell biology     

The galenic and hippocratic challenges to Aristotle's conception theory

Conclusion As a result of this case study, additional questions arise. These can be cast into at least three groups. The first concerns the development of critical empiricism in the ancient world: a topic of much interest in our own century, expecially with regard to the work of the logical empiricists. Many of the same arguments are present in the ancient world and were hotly debated from the Hippocratic writers through and beyond Galen. Some of the ways in which Galen reacts to Hippocratic and Aristotelian influences may, in part, be explained by Galen's own posture as a so-called Dogmatist. Both the Empirics and the Methodists offered alternative viewpoints on the place, role, and limits of observation in biomedical research. Though I have written on this relationship in the Hippocratic writers and Aristotle,⁴⁴ it remains to be discussed in detailed fashion just how critical empiricism acted in Galen's evaluation of biomedical problems (aporiai). Contrasts between Galen and his predecessors might further clarify this issue both as a historical question and as it affects the construction of biological theory.The second area explores the question of how one develops comprehensive theories. In this respect Galen follows Aristotle's methodology rather closely. Both look at what theories are available to them and then systematically review the problems raised, at the same time refuting what they find inadequate. This is an effective strategy, for it permits utilizing the best features of earlier work to fashion a new whole. Indeed, Galen himself seems to attribute his use of such a methodology to his ecletic medical and philosophical training. Both Aristotle and Galen endeavor to employ techniques of theory integration. That is, they use aspects of theories they have already espoused to deal with new problems. This suggests the emergence of formal, logical coherence as an element in theory evaluation. The obvious drawback is that it can cause mistakes in one area to be repeated and ingrained in other areas. Such errors, because they are at the very core of an explanatory framework, may take centuries to correct. Future studies may shed light on how theory integration acts both in a positive and in a negative way.Finally, this case study offers a glimpse of how science progresses. Even though the advances in medical technology were comparatively minor, there is a great deal more sophistication in the conception theoreis of Aristotle and Galen than was present in the Hippocratic writers. Some of this (in Galen's case) had to do with increased anatomic and physiological knowledge, but most, I believe, is due to the evolution of scientific knowledge. If further work were done specifically on this question, it might document more completely how scientific knowledge on a specific topic evolves. The mode of advancement is primarily through gradual refinement of the types of questions being asked by these ancient authors, and the ramifications of their answers.Ancient theories of conception offer a fine case study in the history and philosophy of how a theory begins the develops. I have tried to suggest some interrelationships among the more important theories, as they focused upon Aristotle's own conception theory. There has been renewed interest in such cases in recent years. It is my hope that future specialized studies will increase our knowledge of method and practice in these important case studies and thereby augment our understanding of the genesis and application of biological theories.