Genetisch bedingte Tumoren und der Gehalt an freien Aminosäuren bei lebendgebärenden Zahnkarpfen (Poeciliidae)

Summary The F₁- and F_nR-hybrids ofPlatypoecilus maculatus andXiphophorus helleri (Poeciliidae), producing melanomase spontaneously, contain essentially more free amino acids than the initial species. Further experiments show that the abnormally high content of free amino acids is connected with the spontaneous formation of tumors.

---

---

Den Herren Prof. Dr.G. de Lattin (Zoologisches Institut Saarbrücken) und Prof. Dr.B. Eistert (Institut für organische Chemie Saarbrücken) sind wir für die stete Förderung dieser Arbeit zu grösstem Dank verpflichtet. Den Herren Prof. Dr.C. Kosswig (Hamburg), Prof. Dr.M. Gordon (New York) und Dr.H. Breider (Würzburg) sind wir für viele Anregungen und die freundliche Überlassung von Zuchtstämmen sehr dankbar. — Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

---

F. Anders, F. Vester, K. Klinke undH. Schumacher, Biol. Zbl., im Druck.     

Direct observation of the alignment of ferromagnetic spins by antiferromagnetic spins

The arrangement of spins at interfaces in a layered magnetic material often has an important effect on the properties of the material. One example of this is the directional coupling between the spins in an antiferromagnet and those in an adjacent ferromagnet, an effect first discovered in 1956 and referred to as exchange bias. Because of its technological importance for the development of advanced devices such as magnetic read heads and magnetic memory cells, this phenomenon has received much attention. Despite extensive studies, however, exchange bias is still poorly understood, largely due to the lack of techniques capable of providing detailed information about the arrangement of magnetic moments near interfaces. Here we present polarization-dependent X-ray magnetic dichroism spectro-microscopy that reveals the micromagnetic structure on both sides of a ferromagnetic-antiferromagnetic interface. Images of thin ferromagnetic Co films grown on antiferromagnetic LaFeO3 show a direct link between the arrangement of spins in each material. Remanent hysteresis loops, recorded for individual ferromagnetic domains, show a local exchange bias. Our results imply that the alignment of the ferromagnetic spins is determined, domain by domain, by the spin directions in the underlying antiferromagnetic layer.     

Deregulation of a Ca2+/calmodulin-dependent kinase leads to spontaneous nodule development

Induced development of a new plant organ in response to rhizobia is the most prominent manifestation of legume root-nodule symbiosis with nitrogen-fixing bacteria. Here we show that the complex root-nodule organogenic programme can be genetically deregulated to trigger de novo nodule formation in the absence of rhizobia or exogenous rhizobial signals. In an ethylmethane sulphonate-induced snf1 (spontaneous nodule formation) mutant of Lotus japonicus, a single amino-acid replacement in a Ca2+/calmodulin-dependent protein kinase (CCaMK) is sufficient to turn fully differentiated root cortical cells into meristematic founder cells of root nodule primordia. These spontaneous nodules are genuine nodules with an ontogeny similar to that of rhizobial-induced root nodules, corroborating previous physiological studies. Using two receptor-deficient genetic backgrounds we provide evidence for a developmentally integrated spontaneous nodulation process that is independent of lipochitin-oligosaccharide signal perception and oscillations in Ca2+ second messenger levels. Our results reveal a key regulatory position of CCaMK upstream of all components required for cell-cycle activation, and a phenotypically divergent series of mutant alleles demonstrates positive and negative regulation of the process.