The nitrogen content of a plant is only one of the many plant characteristics that are vitally important to herbivores. However, because of its central role in all metabolic processes as well as in cellular structure and genetic coding, nitrogen is a critical element in the growth of all organisms. Supplementary N often elicits enhanced health, growth, reproduction, and survival in many organisms. This suggests that N is a limiting factor. Since N makes up a large portion of the earth's atmosphere (about 78%), the problem is not an absolute but a relative shortage-that is, a scarcity of usable or metaboliza­ ble N during critical growth periods (159, 328). Plants encounter shortages of inorganic nitrogen (nitrate and/or ammonium ions); animals experience shortages of organic nitrogen (specific proteins and/or amino acids). This article reviews and examines the evidence (a) that N is scarce and perhaps a limiting nutrient for many herbivores, and (b) that in response to this selection pressure, many herbivores have evolved specific behavioral, morphological, physiological, and other adaptations to cope with and uti­ lize the ambient N levels of their normal haunts. McNeill & Southwood (201) and White (328) have also reviewed these general questions. There­ fore, this review explores additional evidence and further develops the fundamental arguments. The review is organized into three major divisions. The first focuses on important sources of variation in plant N (seasonal and ontogenetic trends, different tissues and species, etc) because such variation may be the basis

Herbivory in relation to plant nitrogen content

The revolution that wasn't: a new interpretation of the origin of modern human behavior.

Acenes have long been the subject of intense study because of the unique electronic properties associated with their pi-bond topology. Recent reports of impressive semiconductor properties of larger homologues have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purification, as well as for fabricating organic electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in solution. These new functionalization strategies have recently allowed the synthesis of acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as investigation of their associated structure/property relationships.

The larger acenes: versatile organic semiconductors.

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

https://science.sciencemag.org/content/sci/273/5277/924.full.pdf

Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001.

Various present and future specialized applications of magnets require monodisperse, small magnetic particles, and the discovery of molecules that can function as nanoscale magnets was an important development in this regard. These molecules act as single-domain magnetic particles that, below their blocking temperature, exhibit magnetization hysteresis, a classical property of macroscopic magnets. Such 'single-molecule magnets' (SMMs) straddle the interface between classical and quantum mechanical behaviour because they also display quantum tunnelling of magnetization and quantum phase interference. Quantum tunnelling of magnetization can be advantageous for some potential applications of SMMs, for example, in providing the quantum superposition of states required for quantum computing. However, it is a disadvantage in other applications, such as information storage, where it would lead to information loss. Thus it is important to both understand and control the quantum properties of SMMs. Here we report a supramolecular SMM dimer in which antiferromagnetic coupling between the two components results in quantum behaviour different from that of the individual SMMs. Our experimental observations and theoretical analysis suggest a means of tuning the quantum tunnelling of magnetization in SMMs. This system may also prove useful for studying quantum tunnelling of relevance to mesoscopic antiferromagnets.

Exchange-biased quantum tunnelling in a supramolecular dimer of single-molecule magnets

THE Orgueil meteorite1, a Type I carbonaceous chondrite that fell in France in 1864, has a high carbon content of about 5 per cent. It has been reported to contain several organic compounds, but some of these compounds, notably amino-acids2–4, have been suspected of being terrestrial contaminants4–7. Until recently it has been difficult to determine the extent of the contamination which occurred between the time of fall of a meteorite and its examination in the laboratory. Now, however, the problems of separation of contaminant from indigenous amino-acids in meteorites can be largely overcome by applying gas chromatographic techniques for the separation of D, L enantiomers of amino-acids as their diastereomeric derivatives and the identification of these compounds by gas chromatographic retention times and mass spectral fragmentation patterns. This kind of approach has been used in investigations of the amino-acids in the Murchison and Murray meteorites8–11. Because terrestrial, biogenic amino-acids are commonly of the L configuration, the presence in these meteorites of racemic mixtures of D, L amino-acids suggested a nonbiogenic origin for these compounds. In addition, the presence of amino-acids not commonly found in protein also strongly implied an extraterrestrial, abiotic origin.

Physical Sciences: Evidence for Amino-acids of Extraterrestrial Origin in the Orgueil Meteorite

The amino acid composition and the extent of racemization in several modern and fossil woods are reported The method of analysis is described, and data are presented on the total amino acid concentration, the amino acid ratios, and the enantiomeric ratios in each sample It is found that the amino acid concentration per gram of dry wood decreases with age of the sample, that the extent of racemization increases with increasing age, and that the amounts of aspartic acid, threonine, and serine decrease relative to valine with increasing age The relative racemization rates of amino acids in wood, bone, and aqueous solution are compared, and it is shown that racemization in wood is much slower than in bone or aqueous solution Racemization results for woods from the Kalambo Falls area of Zambia are used to calculate a minimum age of 110,000 years for the transition between the Sangoan and Acheulian industries at that site This result is shown to be consistent with numerous radiometric dates for older Acheulian sites in Africa and to compare well with geologically inferred dates for the beginning of the Eemian and the end of the Acheulian industry in southern Africa

Amino acids in modern and fossil woods

Optically active amino-acids have been found in a sample of PreCambrian Fig Tree chert at least three thousand million years old.

Optical Configuration of Amino-acids in Pre-Cambrian Fig Tree Chert

For almost 20 years laboratory experiments have advanced the concepts of chemical evolution, particularly with regard to formation of the amino acids. What has been generally lacking is concrete natural evidence for this chemical evolution hypothesis. The recent development of sophisticated analytical techniques and availability of carbonaceous chondrites with a minimum of terrestrial contamination has resulted in the identification of amino acids which provide strong evidence for a natural extraterrestrial chemical synthesis. Since the initial find in the Murchison meteorite (a type II carbonaceous chondrite) of both protein and nonprotein amino acids and amino acids with nearly equal abundances of D and L isomers, further studies have been carried out. These studies have revealed the presence of at least 35 amino acids; the population consists of a wide variety of linear, cyclic and polyfunctional amino acids which shows a trend of decreasing concentration with increasing carbon number. Investigations of the Murray meteorite (a type II carbonaceous chondrite) has produced similar results, but studies of the Orgueil meteorite (a type I carbonaceous chondrite) show only a limited suite of amino acids, some of which appear to be indigenous while others appear to be terrestrial contaminants. A sample of the Murchison meteorite was extracted with D2O and in addition to ‘free’ amino acids, showing no deuterium incorporation, some amino acids showed the presence of deuterium suggesting either a ‘precursor(s)’ or hydrogen-deuterium exchange which require(s) formation of carbon-hydrogen bonds.

Amino acids in carbonaceous chondrites.

The problems of separation of contaminant from indigenous amino-acids in meteorites can be largely overcome by applying gas chromatographic techniques for the separation of D,L enantiomers of amino-acids as their diastereomeric derivatives and the identification of these compounds by gas chromatographic retention times and mass spectral fragmentation patterns. Two samples of Orgueil meteorite were examined. The results show that there are amino-acids indigenous to the Orgueil meteorite in addition to those present as contaminants.

Etta Peterson

Papers

Physical Sciences: Evidence for Amino-acids of Extraterrestrial Origin in the Orgueil Meteorite

Amino acids in modern and fossil woods

Optical Configuration of Amino-acids in Pre-Cambrian Fig Tree Chert

Amino acids in carbonaceous chondrites.

Evidence for amino-acids of extraterrestrial origin in the Orgueil meteorite.