Histological study of embryogenesis and organogenesis from anthers ofVitis rupestris du Lot cultured in vitro

Summary Anthers ofVitis rupestris du Lot were cultured in vitro at the uninucleate stage of the microspore, in order to investigate the histology of embryogenic and organogenic processes in this genotype. Microspores divided in the anther loculi resulting in the formation of globular structures with a ruptured exine. Somatic embryogenesis and, occasionally, caulogenesis and rhizogenesis occurred in calli produced from all anther tissues except the endothecium. The initial cell of the embryoid was surrounded by a jacket layer when situated deep within the callus. When the embryoid's initial cell was situated in the peripheral callus, a cutinized wall was present and the three-celled proembryoid was almost always segmented, showing the same embryonal type as the zygotic proembryo. Root differentiation and elongation and cap differentiation occurred during the growth phase in liquid medium. The mature root was diarch and contained cells with calcium-oxalate raphides, as seen in vivo. No starch or tannin deposition was ever observed in the mature embryoids.Abbreviations 6-BAP 6-benzylaminopurine - CC3 Nitsch and Nitsch (1969) basal medium - CS cross section - 2,4-D 2,4-dichlorophenoxy-acetic acid - LS longitudinal section     

Diversity and origins of endophytic fungal symbionts of the North American grass Festuca arizonica

Summary Acremonium spp. endophytes are mutualistic fungal symbionts of many C3 grasses. They are anamorphs of Epichloë typhina (Clavicipitaceae) that have become strictly seedborne, heritable components of symbiotic units (symbiota). In order to test the possibility that endophytes may contribute to the genetic diversity of symbiota, a survey was conducted of plants from nine populations of Festuca arizonica in the southern Rocky Mountains. Sequence analysis of rRNA gene segments distinguished three Acremonium endophyte types. Parsimony analysis indicated at least two distinct evolutionary origins of the Acremonium endophytes from E. typhina. Either or both of these evolutionary lineages may have involved cospeciation with the host.     

Chromosomal location of rDNA in Allium: in situ hybridization using biotin- and fluorescein-labelled probe

Summary A biotin- and fluorescein-labelled probe of Helianthus argophyllus has been used to map specific repeated rDNA sequences by in situ hybridization on mitotic chromosomes of Alliwn cepa, Allium fistulosum, a diploid interspecific (Allium fistulosum x Allium cepa) F₁ hybrid, and a triploid interspecific (2 x = A. cepa, 1 x = A. fistulosum) shallot. Hybridization sites were restricted to satellited and smallest pairs of chromosomes in both A. cepa and A. fistulosum. The number, size, and position of the hybridization sites distinguish homologous chromosomes and identify the individual chromosomes carrying the nucleolus organizing region (NOR) at the secondary constriction, as well as the individual chromosomes carrying an additional NOR. This in situ hybridization technique is the first reported in a plant species and offers new cytogenetic markers in Allium.     

Polymorphism and inheritance of gliadin polypeptides in T. monococcum L.

Summary More than 80 different gliadin electrophoretic patterns (spectra) have been found in 109 accessions of the diploid wheat Triticum monococcum. Each pattern consists of 15–20 gliadin bands. Some patterns are clearly related and might arise from one another through single mutations in the gliadin-coding loci. From the analysis of 15 grains of each, only 61 accessions were found to be uniform; others consisted of two or more grain variants differing in their gliadin spectrum. An analysis of F₂ grains from three crosses between different accessions showed that groups (blocks) of components are jointly and codominantly inherited. Two independent major Gli loci were established. The close resemblance of the composition of some blocks of T. monococcum to some of those in polyploid wheats indicates that one locus in each T. monococcum genotype is located on chromosome 1A (Gli-A1) and the other on 6A (Gli-A2). However, the blocks of T. monococcum include more bands than corresponding (equivalent) blocks of polyploid wheats. Two out of 275 F₂ grains of the cross k-14244 x k-20409 were found to have gliadin spectra which can be explained as a result of intralocus recombination. Also, a second gliadin-coding locus on chromosome 1A was found in the cross k-46140 x k-46753. This locus recombines with the main Gli-A1 locus with a frequency of about 22% and was clearly analogous to the additional Gli locus found earlier on chromosome 1A of certain polyploid wheats.     

Sequence analysis of WIS-2-1A,a retrotransposon-like element from wheat

WIS-2-1A, a 8624 bp insertion in the Glu-1A-2 locus of chromosome 1A of wheat, consists of two 1755 bp long terminal repeats enclosing a 5114 bp internal region. No long open reading frames could be found, but inspection of the predicted amino acid sequence showed regions with homology to retrotransposon structures, including a methionine tRNA initiator binding site, a nucleotide binding domain, a protease, an integrase and a polymerase. DNA replication errors have resulted in frame-shifts in the protein coding region, suggesting that retrotransposition of WIS-2-1A, if it occurs, must be mediated by trans-acting factors.     

The activation process of Arabidopsis thaliana A1 gene encoding the translation elongation factor EF-1α is conserved among angiosperms

In Arabidopsis thaliana, the activation process of the A1 EF-1 gene depends on several elements. Using the GUS reporter gene, transient expression experiments have shown that mutations of upstream cis-acting elements of the A1 promoter, or the deletion of an intron located within the 5 non-coding region, similarly affect expression in dicot or monocot protoplasts. The results reported here strongly suggest that this 5 intron is properly spliced in Zea mays. We show that two trans-acting factors, specifically interacting with an upstream activating sequence (the TEF 1 box), are present in nuclear extracts prepared from A. thaliana, Brassica rapa, Nicotiana tabacum and Z. mays. In addition, a DNA sequence homologous to the TEF 1 box, found at approximately the same location within a Lycopersicon esculentum EF-1 promoter, interacts with the same trans-acting factors. Homologies found between the A. thaliana and L. esculentum TEF 1 box sequences have allowed us to define mutations of this upstream element which affect the interaction with the corresponding trans-acting factors. These results support the notion that the activation processes of A. thaliana EF-1 genes have been conserved among angiosperms and provide interesting data on the functional structure of the TEF 1 box.     

A statistical comparison of various factors on embryogenic proliferation,morphogenesis and regeneration in Lolium temulentum cell suspension colonies

Cell suspension colonies from four embryogenic Lolium temulentum lines were selected and plated individually in 25 embryoid maturation treatments which varied in various factors reported to stimulate embryogenesis or improve regeneration. Using a numerical scoring system to compare the cultures against a control, treatments were identified which increased growth, suppressed morphogenesis or encouraged premature shoot formation.No treatment significantly improved the proportion of colonies with globular or mature embryoids, but some prevented maturation and increased the proportion with translucent embryogenic proliferation. Other treatments accelerated maturation causing increased de-differentiation of embryogenic tissues. These treatments also tended to discourage the differentiation of discreet embryoids.Colonies were later transferred en masse to a regeneration medium and scored using another numerical system. Embryoid maturation conditions were then identified which increased or suppressed subsequent shoot regeneration. The two scoring systems enabled cultures of the four lines to be characterised in detail and identified somatic variation in embryogenic development, morphogenesis and de-differentiation.     

Some comments on coordinate-free and scale-invariant methods in morphometrics

The unusual strategy for comparing biological shapes is to use some kind of superimposition of the two forms under study and then look at the "residuals" as the shape change. In this paper, I take a careful look at this general strategy and point out some subtle but inherent and important pitfalls. Additionally an alternative approach based on Euclidean Distance Matrix representation is presented. It is applicable to two- as well as three-dimensional objects.     

Association of soybean root mycoflora with root modulation, root necrosis and plant fresh weight

Fungi were isolated from soybean plants in ten fields in south-west France. Correspondence analysis (COA) was used to find associations among taxa (species, genera, groups) and sampling units (i.e. one field at one sampling date). The first axis of the COA demonstrated a dominant sampling date effect; the second indicated an association among certain sampling units and specific taxa. Regression analysis of COA coordinate values indicated that fields with high relative isolation frequencies of Fusarium spp., F. oxysporum and ‘other species’ (mostly Chaetomium spp. and sterile fungi) were characterised by greater plant fresh weight and nodule number and lower ratings for root necrosis. Cylindrocarpon spp., Cephalosporium spp. and F. solanihad high relative isolation frequencies in fields with lower plant weight, lower nodule number and higher root necrosis ratings. The relative importance of fungal taxa was also related to soil type.