Marc Behr

Impact of Grape Cluster Division on Cluster Morphology and Bunch Rot Epidemic

Manual horizontal cluster division may constitute an efficient tool to optimize wine composition. To test this hypothesis and to determine the optimal timing of this viticultural practice, the impact of cluster division on cluster morphology, bunch rot disease severity, and harvest parameters such as yield and total soluble solids was examined on the white Vitis vinifera L. cultivars Pinot gris and Riesling in the Luxembourgish winegrowing region in 2010 and 2011. Treatments were applied at five different times between prebloom (BBCH 57) and veraison (BBCH 81). In both varieties, all postbloom cluster division treatments were able to loosen the cluster structure and reduce the bunch rot disease severity. The later cluster division took place, the more pronounced were the effects on cluster structure. The density index was a suitable measure of the cluster structure and the predisposition to bunch rot infestation. Cluster division resulted in yield reductions (up to 30%), which increased with time after flowering. Postbloom cluster division may help to optimize wine quality by improving grape maturity due to crop load reduction, reducing fungal contamination, and improving grape composition through the possibility of elongating the ripening period. Postbloom horizontal cluster division can be recommended as an efficient crop cultural tool for premium wine production under cool-climate conditions.

Analysis of Cell Wall-Related Genes in Organs of Medicago sativa L. under Different Abiotic Stresses

Abiotic constraints are a source of concern in agriculture, because they can have a strong impact on plant growth and development, thereby affecting crop yield. The response of plants to abiotic constraints varies depending on the type of stress, on the species and on the organs. Although many studies have addressed different aspects of the plant response to abiotic stresses, only a handful has focused on the role of the cell wall. A targeted approach has been used here to study the expression of cell wall-related genes in different organs of alfalfa plants subjected for four days to three different abiotic stress treatments, namely salt, cold and heat stress. Genes involved in different steps of cell wall formation (cellulose biosynthesis, monolignol biosynthesis and polymerization) have been analyzed in different organs of Medicago sativa L. Prior to this analysis, an in silico classification of dirigent/dirigent-like proteins and class III peroxidases has been performed in Medicago truncatula and M. sativa. The final goal of this study is to infer and compare the expression patterns of cell wall-related genes in response to different abiotic stressors in the organs of an important legume crop.

Studying secondary growth and bast fiber development: The hemp hypocotyl peeks behind the wall

Cannabis sativa L. is an annual herbaceous crop grown for the production of long extraxylary fibers, the bast fibers, rich in cellulose and used both in the textile and biocomposite sectors. Despite being herbaceous, hemp undergoes secondary growth and this is well exemplified by the hypocotyl. The hypocotyl was already shown to be a suitable model to study secondary growth in other herbaceous species, namely Arabidopsis thaliana and it shows an important practical advantage, i.e., elongation and radial thickening are temporally separated. This study focuses on the mechanisms marking the transition from primary to secondary growth in the hemp hypocotyl by analysing the suite of events accompanying vascular tissue and bast fiber development. Transcriptomics, imaging and quantification of phytohormones were carried out on four representative developmental stages (i.e., 6–9–15–20 days after sowing) to provide a comprehensive overview of the events associated with primary and secondary growth in hemp. This multidisciplinary approach provides cell wall-related snapshots of the growing hemp hypocotyl and identifies marker genes associated with the young (expansins, β-galactosidases, and transcription factors involved in light-related processes) and the older hypocotyl (secondary cell wall biosynthetic genes and transcription factors).

Detection and Quantification of Natural Contaminants of Wine by Gas Chromatography–Differential Ion Mobility Spectrometry (GC-DMS)

Rapid and direct, in situ headspace screening for odoriferous volatile organic compounds (VOCs) present in fresh grapes and in wines is a very promising method for quality control because the economic value of a wine is closely related to its aroma. Long used for the detection of VOCs in complex mixtures, miniature differential ion mobility spectrometry (DMS) seems therefore adequate for in situ trace detection of many kinds of VOCs of concern appearing in the headspace of selected foodstuffs. This work aims at a rapid detection, identification, and quantification of some natural and volatile contaminants of wine such as geosmin, 2-methylisoborneol (2-MIB), 1-octen-3-ol, 1-octen-3-one, and pyrazines (2-isopropyl-3-methoxypyrazine, IPMP, and 3-isobutyl-2-methoxypyrazine, IBMP). In the present study, these compounds were spiked at a known concentration in wine and analyzed with a hyphenated trap-GC-DMS device. The detection of all target compounds at concentrations below the human olfactory threshold was demonstrated.

Transcriptomic profiling of hemp bast fibres at different developmental stages.

Bast fibres are long extraxylary cells which mechanically support the phloem and they are divided into xylan- and gelatinous-type, depending on the composition of their secondary cell walls. The former, typical of jute/kenaf bast fibres, are characterized by the presence of xylan and a high degree of lignification, while the latter, found in tension wood, as well as flax, ramie and hemp bast fibres, have a high abundance of crystalline cellulose. During their differentiation, bast fibres undergo specific developmental stages: the cells initially elongate rapidly by intrusive growth, subsequently they cease elongation and start to thicken. The goal of the present study is to provide a transcriptomic close-up of the key events accompanying bast fibre development in textile hemp (Cannabis sativa L.), a fibre crop of great importance. Bast fibres have been sampled from different stem regions. The developmental stages corresponding to active elongation and cell wall thickening have been studied using RNA-Seq. The results show that the fibres sampled at each stem region are characterized by a specific transcriptomic signature and that the major changes in cell wall-related processes take place at the internode containing the snap point. The data generated also identify several interesting candidates for future functional analysis.

Research note: benefits and drawbacks of pre-bloom applications of gibberellic acid (GA3) for stem elongation in Sauvignon blanc.

Dense grape clusters have a high predisposition to bunch rot. An elongation of cluster stems could result in a loosening of the cluster structure. To achieve such an elongation, gibberellic acid (GA3; 10 ppm) was applied to Sauvignon blanc either when three, five, seven, nine, 11 or 13 leaves were unfolded or at full bloom in the 2010 season. In the present season, all applications led to stem elongation, a reduction of cluster compactness as well as a reduction of bunch rot severity. The density index proved to be an efficient tool to describe the predisposition of grape clusters to bunch rot. Best success was achieved if the application took place when seven leaves were unfolded. In the subsequent season (2011; the year following the year of application), the number of inflorescences per shoot, the length of the clusters, as well as the yield were considerably reduced, especially in the treatments with promising positive effects on the cluster structure and disease severity. Hence, the present study shows the loosening potential as well as the risk of pre-bloom gibberellic acid applications. Due to the observed negative resultant effects, the pre-bloom application of GA3 at the present concentration (10 ppm) cannot yet be recommended for practical use in Sauvignon blanc.

Earthy and Fresh Mushroom Off-Flavors in Wine: Optimized Remedial Treatments

Geosmin and 1-octen-3-one are the causal agents of earthy-muddy and fresh mushroom off-flavors. Several products are available to remove these off-flavors and are commonly used at different steps of winemaking for various applications. This research evaluated and compared the efficiencies of those commercial products, including activated carbons, chitosans, zeolites, and filtrations, on white wine. For each product, different doses were evaluated on wine spiked at 200 ng/L of geosmin or 1-octen-3-one and were measured by GC-MS/MS. Several formulations of activated carbon provided good efficiencies for geosmin removal, as well as a filtration dedicated to off-flavor removal. However, chitosans and zeolites generally did not reach a satisfactory level. Activated carbons were also able to reduce the concentration of 1-octen-3-one.

Didehydrophenylalanine, an abundant modification in the beta subunit of plant polygalacturonases

The structure and the activity of proteins are often regulated by transient or stable post- translational modifications (PTM). Different from well-known, abundant modifications such as phosphorylation and glycosylation some modifications are limited to one or a few proteins across a broad range of related species. Although few examples of the latter type are known, the evolutionary conservation of these modifications and the enzymes responsible for their synthesis suggest an important physiological role. Here, the first observation of a new, fold-directing PTM is described. During the analysis of alfalfa cell wall proteins a -2Da mass shift was observed on phenylalanine residues in the repeated tetrapeptide FxxY of the beta-subunit of polygalacturonase. This modular protein is known to be involved in developmental and stress-responsive processes. The presence of this modification was confirmed using in-house and external datasets acquired by different commonly used techniques in proteome studies. Based on these analyses it was found that all identified phenylalanine residues in the sequence FxxY of this protein were modified to α,β-didehydro-Phe (ΔPhe). Besides showing the reproducible identification of ΔPhe in different species arguments that substantiate the fold-determining role of ΔPhe are given.

Description of the mechanisms underlying geosmin production in Penicillium expansum using proteomics

UNLABELLED A 2D-DIGE proteomics experiment was performed to describe the mechanism underlying the production of geosmin, an earthy-smelling sesquiterpene which spoils wine, produced by Penicillium expansum. The strains were identified by sequencing of the ITS and beta-tubulin regions. This study was based on a selection of four strains showing different levels of geosmin production, assessed by GC-MS/MS. The proteomics study revealed the differential abundance of 107 spots between the different strains; these were picked and submitted to MALDI-TOF-TOF MS analysis for identification. They belonged to the functional categories of protein metabolism, redox homeostasis, metabolic processes (glycolysis, ATP production), cell cycle and cell signalling pathways. From these data, an implication of oxidative stress in geosmin production may be hypothesized. Moreover, the differential abundance of some glycolytic enzymes may explain the different patterns of geosmin biosynthesis. This study provides data for the characterisation of the mechanism and the regulation of the production of this off-flavour, which are so far not described in filamentous fungi. BIOLOGICAL SIGNIFICANCE Green mould on grapes, caused by P. expansum may be at the origin of off-flavours in wine. These are characterized by earthy-mouldy smells and are due to the presence of the compound geosmin. This work aims at describing how geosmin is produced by P. expansum. This knowledge is of use for the research community on grapes for understanding why these off-flavours occasionally occur in vintages.

Jasmonic acid to boost secondary growth in hemp hypocotyl

Main conclusionThe application of jasmonic acid results in an increased secondary growth, as well as additional secondary phloem fibres and higher lignin content in the hypocotyl of textile hemp (Cannabis sativa L.).Secondary growth provides most of the wood in lignocellulosic biomass. Textile hemp (Cannabis sativa L.) is cultivated for its phloem fibres, whose secondary cell wall is rich in crystalline cellulose with a limited amount of lignin. Mature hemp stems and older hypocotyls are characterised by large blocks of secondary phloem fibres which originate from the cambium. This study aims at investigating the role of exogenously applied jasmonic acid on the differentiation of secondary phloem fibres. We show indeed that the exogenous application of this plant growth regulator on young hemp plantlets promotes secondary growth, differentiation of secondary phloem fibres, expression of lignin-related genes, and lignification of the hypocotyl. This work paves the way to future investigations focusing on the molecular network underlying phloem fibre development.