Signalling and cell death in ozone-exposed plants

Experiments with Arabidopsis mutants and sensitive and tolerant pairs in several other species have elucidated the molecular basis of plant ozone sensitivity and ozone lesion development. They have indicated an important role for hormonal signalling in determining the outcome of ozone challenge at the cellular level. The reactive oxygen species (ROS) from ozone degradation can cause either direct necrotic damage or induce the process of programmed cell death. Perception of ozone or ROS from its degradation in the apoplast activates several signal transduction pathways that regulate the responses of the cells to the increased oxidative load. Plant hormones salicylic acid, jasmonic acid, ethylene and abscisic acid are involved in determining the duration and extent of ozone-induced cell death and its propagation. Salicylic acid is required for the programmed cell death, ethylene promotes endogenous ROS formation and lesion propagation, and jasmonic acid is involved in limiting the lesion spreading. Abscisic acid is most likely involved through the regulation of stomata and thus is expected to affect lesion initiation. The roles and interactions of perception of ozone, the immediate downstream responses, hormone biosynthesis and signalling during ozone lesion initiation and formation are reviewed.     

Morphometric analysis and taxonomic revision of Anisopteromalus Ruschka (Hymenoptera: Chalcidoidea: Pteromalidae) – an integrative approach

We use an integrative taxonomic approach to revise the genus Anisopteromalus. In particular, we apply multivariate ratio analysis (MRA), a rather new statistical method based on principal component analysis (PCA) and linear discriminant analysis (LDA), to numerous body measurements and combine the data with those from our molecular analysis of Cytb and ITS2 genetic markers (on a subset of species) and all available published data on morphology, karyology, behaviour, host associations and geographic distribution. We demonstrate that the analysis of quantitative characters using MRA plays a major role for the integration of name‐bearing types and thus for the association of taxa with names. Six species are recognized, of which two are new: A. cornis Baur sp.n. and A. quinarius Gokhman & Baur sp.n. For Anisopteromalus calandrae (Howard), a well‐known, cosmopolitan parasitoid of stored‐product pests, we have selected a neotype to foster continuity and stability in the application of this important name. The species was sometimes confused with the related A. quinarius sp.n. , another cosmopolitan species that is frequently encountered in similar environments. We also show that several species originally described or later put under Anisopteromalus actually belong to different genera: Cyrtoptyx camerunus (Risbec) comb.n. ; Meraporus glaber (Szelényi) comb.n. ; Dinarmus schwenkei (Roomi, Khan & Khan) comb.n. Neocatolaccus indicus Ayyar & Mani is confirmed as a junior synonym of Oxysychus sphenopterae (Ferrière) syn.n. and Anisopteromalus calandrae brasiliensis (Domenichini) stat.rev. must be considered as a valid but doubtful taxon. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:BDFE96D3‐D0F4‐4012‐90F5‐9A087F7F5864 .     

Die Vaskularisation der Kiemen von Myxine glutinosa L. (Cyclostomata)

The angioarchitecture of the gills in Myxine glutinosa L. was studied by scanning electron microscopy of vascular corrosion casts (methylmethacrylate). It was found that the afferent branchial artery may be connected to the sinus peribranchialis by a papilla. The sinus is connected to delicate vessels and sinuses, which are interposed between meridionally arranged radial arteries. These delicate vascular formations continue into the interior of the gill and form a plexus on both poles of the gill folds. Light and scanning electron microscopical studies on the vascular endothelium of the afferent vessels of the gill lamellae reveal rounded endothelial cells, which are characterized by a high content of granula, by long cellular processes and by bridge-formations towards neighbouring cells. Supporting columns within the vascular system of the lamellae were found to be set up by several spirally arranged cells. SEM observations reveal goblet cells and numerous superficial epithelial cells with various numbers of microvilli and microridges forming the epithelial surface of the gill folds.     

Natural variation in ozone sensitivity among Arabidopsis thaliana accessions and its relation to stomatal conductance

Genetic variation between naturally occurring populations provides a unique source to unravel the complex mechanisms of stress tolerance. Here, we have analysed O₃ sensitivity of 93 natural Arabidopsis thaliana accessions together with five O₃‐sensitive mutants to acute O₃ exposure. The variation in O₃ sensitivity among the natural accessions was much higher than among the O₃‐sensitive mutants and corresponding wild types. A subset of nine accessions with major variation in their O₃ responses was studied in more detail. Among the traits assayed, stomatal conductance (g_st) was an important factor determining O₃ sensitivity of the selected accessions. The most O₃‐sensitive accession, Cvi‐0, had constitutively high g_st, leading to high initial O₃ uptake rate and dose received during the first 30 min of exposure. Analyzing O₃‐induced changes in stress hormone concentrations indicated that jasmonate (JA) concentration was also positively correlated with leaf damage. Quantitative trait loci (QTL) mapping in a Col‐0 × Cvi‐0 recombinant inbred line (RIL) population identified three QTLs for O₃ sensitivity, and one for high water loss of Cvi‐0. The major O₃ QTL mapped to the same position as the water loss QTL further supporting the role of stomata in regulating O₃ entry and damage.