THE HISTOLOGY OF THE NECROTIC LESIONS INDUCED BY VIRUS DISEASES

About 12 hours after a leaf of Nicotiana glutinosa is inoculated with ancuba mosaic disease a band of necrotic material begins to form within the cell wall, usually between the lower epidermis and the spongy parenchyma. This band extends both laterally and towards the upper side of the leaf. At the same time, nuclear division is observed in the spongy parenchyma cells, but karyokinesis is not followed by cell division. As the necrotic mesh work extends the cells within it die and dry out. After about 3 days, the lesion consists of a meshwork of this necrotic material. The cells are all dead and the virus is isolated within the necrotic area, all interchange between the infected and healthy parts of the leaf having been prevented.
I am indebted to Fraulein Lina Cunow for assistance in making the preparations used in this study.     

Models of sexual and asexual coexistence in aphids based on constraints

Two models are presented to test the hypothesis that in aphids, a particular constraint (the necessity to resist frost) could be the proximal cause for the maintenance of sex. Both models are based on temporal variability in winter survival of asexuals. They show that:

• i) only cyclical parthenogenesis is maintained below a threshold frequency of mild winters, because of the cold-resistance of sexually-produced eggs.
• ii) above a second threshold, only obligate parthenogenesis is maintained.
• iii) in-between, the first model predicts a mixed evolutionarily stable strategy (ESS). This would reflect well the geographic distribution of the different types of reproduction. The second model, based on the genetic control of the reproduction system in two aphid species, predicts the maintenance of polymorphism with fluctuating proportions of the two life-cycles. Males produced by obligate parthenogens play an essential role in this equilibrium (no stable polymorphism exists if this male production is set to zero). The value of the lowest possible fitness achieved by overwintering asexuals is critical.

     

The units ofselection

The individual has long been considered by evolutionists to be the only level at which selection acts. Recent advances in molecular biology have forced them to accept at least one other, the molecular level. This paves the way for a broadening of perspective in evolutionary thought, but renders it more necessary to clarify the debate about the level at which the process of evolution occurs. This debate cannot be resolved without clarifying the premises on which the argument is based. To this end, it is helpful to distinguish between that which is transmitted and that which transmits. The discrimination of genetic information from its material support (avatar) can be most useful, particularly when placed in the context of the hierarchical organization of biological systems. The utility of this approach is exemplified by its application to the case of the evolution of sex.     

Aperture pattern ontogeny in angiosperms

Pollen grains display a wide range of variation in aperture number and arrangement (pattern) in angiosperms. Apertures are well-defined areas of the pollen wall surface that permit pollen tube germination. For low aperture numbers, aperture patterns are characteristic of the major taxonomic divisions of angiosperms. This paper presents a developmental model that explains most of the aperture patterns that are recorded in angiosperms. It is based on the analysis of the different events that occur during meiosis and lead to microspore differentiation. It demonstrates that variation occurring during meiosis in angiosperms is sufficient to produce the core morphological set of the most commonly observed pollen morphologies.     

Correlated variation in microtubule distribution, callose deposition during male post-meiotic cytokinesis, and pollen aperture number across Nicotiana species (Solanaceae)

In most flowering plants, a single cytokinesis follows the two meiotic divisions during pollen-grain ontogeny. Aperture pattern (i.e., aperture number and distribution on pollen surface) ontogeny could be linked to the processes ensuring the apportionment of the cytoplasm to the four microspores.This apportionment is achieved by radial arrays of microtubules organized around the nuclei. The cleavage planes are defined in the overlapping regions of opposing arrays extending from different nuclei. We followed the establishment of these arrays in two different lines of plants belonging to the genus Nicotiana that produce pollen grains with different aperture numbers. Different distributions of the microtubules have been observed, which can be interpreted as resulting from variation in the interactions between nuclei; these distributions appear to be correlated with aperture number.As a consequence, we propose that simultaneous cytokinesis allows the formation of multiple pollen morphologies. This mechanism is consistent with aperture number distribution within angiosperms and provides clues to help our understanding of the evolution of aperture number.     

Complementary effects of adenosine and angiotensin II in hypoxemia-induced renal dysfunction in the rabbit

The acute renal effects of hypoxemia and the ability of the co-administration of an angiotensin converting enzyme inhibitor (perindoprilat) and an adenosine receptor antagonist (theophylline) to prevent these effects were assessed in anesthetized and mechanically-ventilated rabbits. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by the clearances of para-aminohippuric acid and inulin, respectively. Each animal acted as its own control. In 8 untreated rabbits, hypoxemia induced a significant drop in mean blood pressure (-12 +/- 2%), GFR (-16 +/- 3%) and RBF (-12 +/- 3%) with a concomitant increase in renal vascular resistance (RVR) (+ 18 +/- 5%), without changes in filtration fraction (FF) (-4 +/- 2%). These results suggest the occurrence of both pre- and postglomerular vasoconstriction during the hypoxemic stress. In 7 rabbits pretreated with intravenous perindoprilat (20 microg/kg), the hypoxemia-induced changes in RBF and RVR were prevented. FF decreased significantly (-18 +/- 2%), while the drop in GFR was partially blunted. These results could be explained by the inhibition of the angiotensin-mediated efferent vasoconstriction by perindoprilat. In 7 additional rabbits, co-administration of perindoprilat and theophylline (1 mg/kg) completely prevented the hypoxemia-induced changes in RBF (+ 11 +/- 3%) and GFR (+ 2 +/- 3%), while RVR decreased significantly (-14 +/- 3%). Since adenosine and angiotensin II were both shown to participate, at least in part, in the renal changes induced by hypoxemia, the beneficial effects of perindoprilat and theophylline in this model could be mediated by complementary actions of angiotensin II and adenosine on the renal vasculature.     

The effects of incomplete protein interaction data on structural and evolutionary inferences

Background  

Present protein interaction network data sets include only interactions among subsets of the proteins in an organism. Previously this has been ignored, but in principle any global network analysis that only looks at partial data may be biased. Here we demonstrate the need to consider network sampling properties explicitly and from the outset in any analysis.     

BioTRIZ Suggests Radiative Cooling of Buildings Can Be Done Passively by Changing the Structure of Roof Insulation to Let Longwave Infrared Pass

This paper demonstrates the application of a design tool called BioTRIZ. Its developers claim that it can be used to access biological strategies for solving engineering problems. Our aim is to design a roof for hot climates that gets free cooling through radiant coupling with the sky. The insulation in a standard roof stops the sun and convection from warming the thermal mass. But it also restricts the mass＇s longwave view of the cool sky. Different solutions to this conflict are offered by BioTRIZ. The chosen solution is to replace the standard insulation component with an open cell honeycomb. The vertical cells would allow longwave radiation to pass, while arresting convection. The solutions offered by BioTRIZ＇s technological counterpart include no such changes in structure. It is estimated that the thermal mass in the biomimetic roof would remain on average 4.5℃ cooler than in a standard roof over a year in Riyadh, Saudi Arabia.