Molecular characterization of homologues of both subunits A (SPO11) and B of the archaebacterial topoisomerase 6 in plants.

The Spo11 protein is an eukaryotic homologue of the topoisomerase 6 subunit A from archaebacteria. In yeast Spo11p has been found to bind covalently to double-strand breaks (DSBs) during meiosis. Single homologues of the SPO11 gene exist in various eukaryotes, except plants. Previously, we found in the Arabidopsis thaliana genome two ancient paralogs, AtSPO11-1 and 2. Here we report on the molecular characterization of a third one, AtSPO11-3. This puzzling finding might be explained by the fact that we detected additionally--for the first time outside of the archaebacterial kingdom--a homologue of the subunit B of topoisomerase 6, AtTOP6B. Both AtSPO11-3 and AtTOP6B are abundantly expressed in Arabidopsis and EST comparisons indicate the presence of both genes in various plant species. Via two hybrid studies we could demonstrate that full length AtTop6B is able to interact with AtSpo11-2 and 3 but not with AtSpo11-1. Our data suggest that plants possess in contrast to other eukaryotes an additional archaebacterial kind of topoisomerase.     

Light,puberty, and aggression: A proximal mechanism hypothesis

Rapidly accumulating evidence indicates that light reduces the human pineal's inhibitory effect on the gonads. Artificially extended daily photoperiods, by allowing increased production of gonadal steroids, have probably accentuated the secular growth trend and may be causing males, especially adolescents and young adults, to have an overready hormonal response to situations which elicit aggressive behavior.The author thanks George M. Vaughan, Harry J. Lynch, Mark D. Altschule, Edmund M. Dewan, Solomon H. Katz, George Adelman, John Ott, and Melvin J. Konner for much needed encouragement and edification. Thanks also to Heide Duda and Wesley Taoka (Countway Library, reference desk, Harvard Medical School) for gracious help on so many occasions.     

Der basipetale [2-14C] Abscisinsäuretransport in Wurzeln intakter Bohnenkeimlinge und seine Bedeutung für den Wurzelgeotropismus

Summary One h and 3 h after point source application of [2-¹⁴C] ABA to the upper side of geotropically stimulated root tips of intact seedlings of Phaseolus coccineus L. a weak downward lateral transport of radioactivity was observed. A clear upward lateral translocation, however, occurred when ABA was applied to the lower side of the root tip. Thus a uniform distribution of radioactivity was established in horizontal roots regardless of the site of the application point, while in upright roots the distribution was asymmetric. Six h after ABA injection radioactivity was uniformly distributed in both the vertical and horizontal root tips.

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Abkürzungen ABA Abscisinsäure - dpm disintegrations perminute - FG Frischgewicht - GA Gibberellinsäure     

The uptake and flow of C, N and ions between roots and shoots in Ricinus communis L. II. Grown with low or high nitrate supply

Seedlings of Ricinus communis L. cultivated in quartz sand weresupplied with a nutrient solution containing either 0.2 molm^–3