Peter Chaerle

An easy and versatile embedding method for transverse sections

In several research areas, transverse sections are indispensable for studying structural aspects of specimens. However, the oriented embedding of small cylindrical samples can become problematic, especially when transverse sections at right angles to the main axis of the object are desired. Here, we describe an easy and low‐cost technique for oriented embedding of small (∅ < 500 µm) as well as of larger specimens (∅ > 500 µm). The usefulness of the technique is demonstrated for roots and stamens of Arabidopsis thaliana and for adventitious roots of Asplenium demerkense, as examples of small and larger cylindrical samples, respectively. Furthermore, several types of resin (glycol methacrylate, epoxy and acrylic resins) were successfully tested, showing the applicability of the technique for light and electron microscopy and for immunolocalizations. In conclusion, the principle of the technique can be extended to several resins and a wide variety of specimen types, such as stems, leaves and textile fibres. The originality of the technique lies in its simplicity combined with its high efficiency to produce well‐oriented transverse sections.

Cytosolic Hydroxymethyldihydropterin Pyrophosphokinase/Dihydropteroate Synthase from Arabidopsis thaliana A SPECIFIC ROLE IN EARLY DEVELOPMENT AND STRESS RESPONSE

In plants, 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase/7,8-dihydropteroate synthase (mitHPPK/DHPS) is a bifunctional mitochondrial enzyme, which catalyzes the first two consecutive steps of tetrahydrofolate biosynthesis. Mining the Arabidopsis genome data base has revealed a second gene encoding a protein that lacks a potential transit peptide, suggesting a cytosolic localization of the isoenzyme (cytHPPK/DHPS). When the N-terminal part of the cytHPPK/DHPS was fused to green fluorescent protein, the fusion protein appeared only in the cytosol, confirming the above prediction. Functionality of cytHPPK/DHPS was addressed by two parallel approaches: first, the cytHPPK/DHPS was able to rescue yeast mutants lacking corresponding activities; second, recombinant cytHPPK/DHPS expressed and purified from Escherichia coli displayed both HPPK and DHPS activities in vitro. In contrast to mitHPPK/DHPS, which was ubiquitously expressed, the cytHPPK/DHPS gene was exclusively expressed in reproductive tissue, more precisely in developing seeds as revealed by histochemical analysis of a transgenic cytHPPK/DHPS promoter-GUS line. In addition, it was observed that expression of cytHPPK/DHPS mRNA was induced by salt stress, suggesting a potential role of the enzyme in stress response. This was supported by the phenotype of a T-DNA insertion mutant in the cytHPPK/DHPS gene, resulting in lower germination rates as compared with the wild-type upon application of oxidative and osmotic stress.

A combined morphometric and AFLP based diversity study challenges the taxonomy of the European members of the complex Prunus L. section Prunus

Multivariate analysis of both endocarp and leaf morphometrics is combined with cluster analysis and Bayesian inference of AFLP markers to assess the morphologic and genetic variation of five European members of Prunus section Prunus (P. cerasifera, P. domestica, P. insititia, P. spinosa, and P. × fruticans). Endocarp morphometrics separate most Prunus taxa studied, but overlap remains between P. domestica and P. cerasifera, and P. spinosa and P. × fruticans. Leaf morphometrics yield better separation of P. domestica and P. cerasifera, but do not allow distinction between P. spinosa and P. × fruticans. Both cluster analysis and PCoA of AFLP markers equally produce three distinct clusters. A first consists of all P. cerasifera samples and the sole P. cocomilia; a second cluster includes all individuals of P. domestica and P. insititia; and a third group comprises all P. spinosa and P. × fruticans samples.

Comparison of different treatments for LM and SEM studies and systematic value of pollen grains in Cyperaceae

The pollen grain morphology of 30 species of 27 genera from the four subfamilies of the Cyperaceae have been studied with LM and SEM. Several methods were tested in order to find the optimal treatment for the delicate Cyperaceae pollen grains. For LM, treatment with wetting agent Agepon and KOH yielded the best results, while critical point drying (CPD) after fixation with alcohol proved to be the best method for studying pollen grains of Cyperaceae with SEM. Our results show that the Mapanioideae have a pollen grain type (only one distal ulcus) clearly different from the other Cyperaceae. Representatives of the examined Sclerioideae and Caricoideae show a similar pollen grain type (mostly one distal ulcus and three lateral pores) while in the Cyperoideae different pollen grain types are found.

Is morphology telling the truth about the evolution of the species rich genus Peperomia (Piperaceae)

Peperomia is with approximately 1,600 species one of the species rich angiosperm genera. Several characters on which current infrageneric classifications are based are influenced by parallel evolution. A well-resolved molecular backbone phylogeny of the genus is needed to address evolutionary questions about morphological traits. Based on separate and combined analyses of a morphological data set and three molecular data sets, phylogenetic relationships within Peperomia are investigated with respect to character evolution. The resulting trees from different datasets are highly congruent. Morphological characters are mapped on a combined molecular tree, visualizing the contrast between previously used homoplastic characters and some newly observed characters, that can be used to delimit monophyletic groups. Length mutational events of the chloroplast dataset are coded and plotted on the respective tree, to test if indels support alternative hypothesis of relationships found in the nuclear datasets as well as the overall performance of indels compared with substitutional mutations. Our findings indicate that length distribution of indels is highest among five and six bp events. Autapomorphic and synapomorphic length mutations are most frequent in both insertions and deletions and are also more frequent independent of the length of the mutation. Concluding, independent of the length, mutations are of phylogenetic importance and should not be disregarded. None of the homoplastic indels turn into synapomorphic indels, supporting the different topology of the nrDNA tree but indicate areas of molecular evolution in favour of length mutations resulting in independent events.

Classical Breeding in Diatoms: Scientific Background and Practical Perspectives

Diatoms are becoming increasingly attractive for scientists and important for various industrial applications. Diatoms are diploid sexual organisms and it is generally accepted that controlled genetic manipulations via sexual reproduction are instrumental for basic diatom research. For more practical aims, e.g., selection and “improvement” of economically relevant diatom strains, the classical breeding approach still remains entirely unexplored. Here, we discuss the potential of this approach for both scientific and practical goals. Our analysis is largely comparative and builds on the knowledge of plant reproductive systems, with emphasis on the experience of manipulating them for applied purposes (plant breeding). We believe this comparison is relevant because of the striking similarity between flowering plants and diatoms in some important biological characteristics including sexuality. The main topics chosen for the evaluation and the comparative analysis are mating systems, breeding procedures, methods of strain selection, potential genetic resources, and consequences of inbreeding.

How to Breed Diatoms: Examination of Two Species with Contrasting Reproductive Biology

The diatoms have become a focus of attention as a potential resource for various industrial applications including biofuel production. Initially, progress can be made by screening species held in culture collections or isolated casually from natural samples. To make significant further advances, however, genetic modification (improvement) of promising species will be necessary, by selecting for economically valuable traits. Most diatoms are sexual organisms, and their genetic manipulation via classical plant breeding methods is desirable and possible, alongside modern approaches, for example, transformation. Here we explore the practicalities of diatom breeding by considering experimental control of sex (in the context of the whole life cycle) in two diatom species, Cyclotella meneghiniana and Seminavis robusta. These diatoms exhibit two different kinds of reproductive system, which are largely representative of the groups to which they belong, that is, the centric and pennate diatoms, respectively. We emphasize that efficient exploration of the potential of sexual breeding will also depend largely on progress in understanding many other fundamental aspects of diatom biology, including species-level taxonomy, population studies and biogeography. Unfortunately, the first genomic models, the centric Thalassiosira pseudonana and the pennate Phaeodactylum tricornutum, cannot be involved in investigations of the fundamentals of breeding behaviour in diatoms since, so far at least, there is no indication that these diatoms have a sexual phase in their life cycles.

A New Species of Asplenium (Aspleniaceae, Pteridophyta) from Ethiopia

ABSTRACT A new species of Asplenium L. from Ethiopia, A. balense Chaerle & Viane, is described and illustrated. This new species is similar to A. demerkense Hieronymus, which differs in rhizome, scales, and frond morphology, and also in the presence of short false veins in the laminae. The new species resembles A. uhligii Hieronymus, but differs in degree of lamina dissection and in the presence of unicellular capitate glands on the indusial margin. Asplenium balense also resembles A. erythraeum Pichi Sermolli, which can be distinguished by the absence of both glands and false veins. Asplenium balense belongs to the group of East African high-altitude (2000–4700 m) Asplenium species similar in gross morphology to members of the A. aethiopicum (Burman f.) Becherer complex. A key to distinguish A. balense from its three most similar, tropical northeast African species (A. demerkense, A. erythraeum, and A. uhligii) is presented.

Additions to the Pteridophyte Flora of Kalimantan, Indonesian Borneo

ABSTRACT A list of 59 newly recorded Pteridophytes from the Bukit Baka- Bukit Raya National Park in Central Kalimantan is presented. Nine species are recorded for Indonesian Borneo (Kalimantan) for the first time: Diplazium polycarpum, Pronephrium peltatum var. persetiferum, Pteris asperula, Selliguea enervis, Sphaerostephanos latebrosus, Sphaerostephanos reconditus, Syngramma quinata, Tectaria tricuspis, and Trichomanes humile. Previously, Sphaerostephanos reconditus, and Tectaria palmata var. dimorpha were only known from their type localities.