Some Problems of the Determination of Stomatal Aperture by the Microrelief Method

The applicability of the microrelief (or reprint) method for stomatal aperture determinations was studied in middle-aged sugar beet leaves. It was found that the picture of the central aperture (CA) of stomata on the reprints could be observed only if their eisoiial aperture (EA) was sufficiently wide. If the width of EA was small (about 1–3 μ), it was impossible to determine the width of CA by means of the reprint method, in view of the proportional dimensions of the upper closing flaps. A lower concentration of the chlorophorm solution of methylmethacrylate used for taking reprints had a favourable influence on the amount of stomata whose width of central aperture was reproduced on the reprints. Simultaneous measurements of the EA-width and of the diffusibility of leaves (determined porometrically) in the course of a day showed, on the whole, fairly corresponding changes. During the wilting of detached leaves their diffusibility fell to zero, where it remained. The width of EA also decreased at first, but at higher water deficits it partly again increased.     

A new sea cow record from the lower Oligocene of western Germany: new indications on the skeletal morphology of Halitherium schinzii (Mammalia: Sirenia)

Since the discovery of the extinct species Halitherium schinzii in the Mainz Basin, sirenian remains from the German Oligocene are usually assigned to this taxon according to the assumption that this would be the only sea cow species there. The attempts of several authors to determine morphological distinctions on the species level remain unconsidered until today. The new find of a partial sea cow skeleton from the lower Oligocene of Bottrop-Kirchheller Heide (western Germany) stirs up the debate on splitting the species currently referred to as H. schinzii. The Bottrop specimen morphologically corresponds to skullcaps from the Mainz Basin and the Belgian Oligocene, which were the basis for the introduction of new species in the past, but are considered synonymous with H. schinzii today. Despite its fragmentary preservation, the new sirenian record reveals shared morphological features mainly referring to the supraoccipital, such as a distinctly rostrad indenting nuchal crest and a reduced external occipital protuberance. These features are in contrast to the prominent morphology of the specimens generally associated with H. schinzii and support the assumed presence of at least two morphotypes in the Oligocene of Central Europe. Additionally, the sea cow from Bottrop-Kirchheller Heide represents the first occurrence of skeletal elements, which are not preserved in the known specimens from this morphotype so far and may contribute to a better understanding of intra- and/or interspecific differences within Sirenia.     

Towards a comprehensive picture of alloacceptor tRNA remolding in metazoan mitochondrial genomes

Remolding of tRNAs is a well-documented process in mitochondrial genomes that changes the identity of a tRNA. It involves a duplication of a tRNA gene, a mutation that changes the anticodon and the loss of the ancestral tRNA gene. The net effect is a functional tRNA that is more closely related to tRNAs of a different alloacceptor family than to tRNAs with the same anticodon in related species. Beyond being of interest for understanding mitochondrial tRNA function and evolution, tRNA remolding events can lead to artifacts in the annotation of mitogenomes and thus in studies of mitogenomic evolution. Therefore, it is important to identify and catalog these events. Here we describe novel methods to detect tRNA remolding in large-scale data sets and apply them to survey tRNA remolding throughout animal evolution. We identify several novel remolding events in addition to the ones previously mentioned in the literature. A detailed analysis of these remoldings showed that many of them are derived from ancestral events.     

Growth rate and total nonstructural saccharides content inAlopecurus pratensis L.

Total nonstructural saccharides (TNS) content in young plant ofAlopecurus pratensis was always above 4% of dry matter even at several types of stress treatment (nitrogen deficiency, low irradiance). TNS content was in negative correlation with concentration of total nitrogen in all cases. Positive correlation was found between the TNS content in plants and relative increase in their root growth rate.