Einige Bemerkungen zur anatomisch-entwicklungsgeschichtlichen Terminologie des Blattes

Zusammenfassung Ausgehend von einer vergleichenden Betrachtung der in der Blattanatomie üblichen Termini und einer Diskussion der damit verbundenen Problematik wird empfohlen, die anatomisch-morphologischen Begriffe dorsiventral und äquifazial sowie die entwicklungsgeschichtlich-histogenetischen Begriffe bifazial und unifazial terminologisch nicht mehr gleichwertig nebeneinander zu verwenden. Dadurch werden die aus der Gegenüberstellung von anatomischen und entwicklungsgeschichtlichen Begriffen resultierenden Alternativen vermieden.Falls man an dem Begriff unifazial festhält, sollte zwischen bifazialdorsiventralen, bifazial-äquifazialen, unifazial-dorsiventralen und unifazialäquifazialen Blättern unterschieden werden; andernfalls reduziert sich das Problem auf eine Einteilung in bifazial-dorsiventrale und bifazial-äquifaziale Blätter.     

The 20 kDa apoprotein of the CP24 complex of photosystem II: An alternative model to study import and intra-organellar routing of nuclear-encoded thylakoid proteins

The 20 kDa polypeptide, the apoprotein of the chlorophyll a/b antenna complex CP24 associated with photosystem II, is a remote relative of light-harvesting complex (LHC) apoproteins and thus a member of the extended cab gene family. LHC apoproteins are poly-topic integral components of the thylakoid membrane with probably three transmembrane segments which originate in nuclear genes and are made in the cytosol as precursors. They possess exclusively stroma-targeting transit peptides for import into the organelle and integrate into the thylakoid membrane via uncleaved hydrophobic domains of the mature protein. The CP24 apoprotein displays intriguing structural differences to LHC apoproteins with a potential impact on the routing and targeting processes during biogenesis. In particular, it lacks a pronounced second hydrophobic segment in the mature polypeptide chain found in LHCPs, and carries a transit peptide that is reminiscent of thylakoid-targeting transit peptides. We have used in organello assays with isolated intact chloroplasts and the authentic precursor of the 20 kDa apoprotein from spinach, or appropriate chimaeric polypeptides consisting of a transit peptide and the mature part of various nuclear-encoded thylakoid proteins of known location and targeting epitopes, in order to resolve the characteristics of its targeting properties, as well as to determine the contribution of the individual parts of the precursor molecule to its import and subsequent intra-organellar routing. Our experiments demonstrate that the transit peptide of the CP24 apoprotein is required only for the import of the protein into the organelle. All subsequent steps, such as the integration of the protein into the thylakoid membrane, binding of chlorophyll, assembly into the CP24 complex and migration to the grana lamellae, still take place if the authentic transit peptide is replaced by a targeting signal of a nuclear-encoded stromal protein.     

Nest-site philopatry and selection for environmental sex determination

The reason for the frequent occurrence of environmental sex determination (ESD) in reptiles is still not well understood, although much effort has been devoted to solving the issue. Stimulated by the occurrence of nest-site philopatry in some species, this paper examines a diploid model of the influence of nest-site philopatry on the evolution of ESD. Analysis shows that nest-site philopatry can lead to ESD because the fitnesses of sons and daughters are not influenced in the same way by nest-site quality. Daughters inherit the nest site and thus benefit more than sons from a high-quality nest site. Conversely, the fitness of daughters at low-quality nest sites is lower compared to the fitness of sons. Therefore, genes causing ESD can spread by causing the production of more sons at low-quality nest sites and more daughters at high-quality nest sites. Suggestions are made to test empirically whether nest-site philopatry led to the evolution of ESD. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct effect of estradiol-17β on progesterone accumulation by ovarian granulosa cells from rhesus monkeys

We have previously demonstrated that estradiol-17β (E₂) administered in vivo induces atresia of the dominant ovarian follicle (DF). Whether this effect is exerted directly at the ovarian level or by central mediation has not been confirmed. The present study was designed to assess whether E₂ in amounts similar to those found in monkey follicular fluid (FF) directly alters in vitro progesterone (P) accumulation by granulosa cells (GC) aspirated from follicles in cycling rhesus monkeys. Follicular contents were aspirated from three to five animals on each of days 8–13 of the cycle. GC were plated at a density of 50,000 viable GC/0.5 ml medium; GC were incubated with 0 or 2–2,000 ng/ml E₂, and cultures were maintained for 72 h. P accumulation by GC collected on day 8 and treated with 2 ng/ml E₂ was augmented 37.5 ± 5.5% (X ± S. E. M.; P<.05) over controls but was diminished significantly at 20 ng/ml ( ?55 ± 18% with respect to controls), 200 ng/ml ( ?73.7 ± 13.2%), and 2,000 ng/ml ( ?77.3 ± 18.4%). A similar dose-response relationship was noted on other cycle days. At a concentration of 2,000 ng/ml, E₂ significantly reduced P 91.5 ± 8.5% (day 10), 81.5 ± 18.5% (day 11), 84.3 ± 4.7% (day 12), and 53.7 ± 15.8% (day 13). We conclude that E₂ at concentrations found in FF can inhibit P output by monkey GC through a direct action.     

VARIATION IN ACOUSTIC SIGNALLING TRAITS EXHIBITS FOOTPRINTS OF SEXUAL SELECTION

Phenotypic variation is ubiquitous in nature and a precondition for adaptive evolution. However, theory predicts that the extent of phenotypic variation should decrease with increasing strength of selection on a trait. Comparative analyses of trait variability have repeatedly used this expectation to infer the type or strength of selection. Yet, the suggested influence of selection on trait variability has rarely been tested empirically. In the present study, I compare estimates of sexual selection strength and trait variability from published data. I constricted the analysis to acoustic courtship traits in amphibians and insects with known variability and corresponding results of female binary choice experiments on these traits. Trait variability and strength of sexual selection were significantly correlated, and both were correlated with signal duration. Because traits under stronger selection had lower variation even after the effect of signal duration was eliminated, I conclude that traces of the strength of selection can be observed with respect to variation of acoustic signaling traits in insects and amphibians. The analysis also shows that traits under stabilizing selection have significantly lower phenotypic variability than traits under directional selection.