No abstract

SummaryParenchyma cells from the inner mesocarp of a grape berry (Vitis vinifera L. cv. Chardonnay) were visualised in three-dimensions within a whole mount of cleared, stained tissue using confocal laser scanning microscopy and digital image reconstruction. The whole berry was ®xed, bisected longitudinally, cleared in methyl salicylate, stained with safranin O and mounted in methyl salicylate. Optical slices were collected at 1.0 mm intervals to a depth of 150 mm. Neighbouring z-series were joined post-collection to double the ®eld-of-view. Attenuation at depth of the¯uorescent signal from cell walls was quanti®ed and corrected. Axial distortion due to refractive index mismatch between the immersion and mounting media was calibrated using yellow-green uorescent microspheres and corrected. Transmission electron microscopy was used to correct¯uorescent measurements of cell wall thickness. Digital image reconstructions of wall-enclosed spaces enabled cells to be rendered as geometric solids of measurable surface area and volume. Cell volumes within the inner mesocarp tissue of a single grape berry exhibited a 14-fold range, with polysigmoidal distribution and groupings around speci®c size classes. Cell shape was irregular and the planes of contact were rarely¯at or simple. Variability in cell shape was indicated by the range in surface area to volume ratios, from 0.080 to 0.198 mm ±1 . Structural detail at the internal surface of the cell wall was apparent. The technique is applicable to a wide range of morphometric analyses in plant cell biology, particularly developmental studies, and reveals details of cell size and shape that were previously unattainable.

Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity.

Abstract.  Thirteen species of Australian acacias are invasive plants in agricultural and native vegetation areas of South Africa. Biological control programmes for Australian acacias in South Africa have been implemented and are aimed at suppressing reproductive vigour and, in some cases, vegetative growth of these weeds. Gall‐forming midges are under consideration as potential biological control agents for invasive acacias in South Africa. Entomological surveys in southern Australia found a diverse cecidomyiid fauna associated with the buds, flowers and fruits of Acacia species. Nine new Dasineura species are described and two species, D. acaciaelongifoliae (Skuse) and D. dielsi Rübsaamen, are redescribed. The newly described taxa are D. fistulosasp.n., D. furcatasp.n., D. glaucasp.n., D. glomeratasp.n., D. oldfieldiisp.n., D. oshanesiisp.n., D. piliferasp.n., D. rubiformissp.n. and D. sulcatasp.n. All eleven species induce galls on ovaries and prevent the formation of fruit. Two general types of gall are caused. Type A comprises woody, tubular galls with larvae living inside ovaries (D. acaciaelongifoliae, D. dielsi, D. fistulosa, D. furcata, D. glauca, D. glomerata, D. oldfieldii). Type B includes soft‐tissued, globose galls that belong to four subtypes: inflated, baglike, hairy galls with larvae living between ovaries (D. pilifera); pyriform, pubescent swellings with larvae living inside ovaries (D. rubiformis); globose, hairy, swellings with larvae living superficially on ovaries in ovoid chambers (D. oshanesii); and inconspicuous, glabrous swellings with larvae living superficially on ovaries in shallow groovelike chambers (D. sulcata). The gall types are associated with a particular pupation pattern. In type A galls, larvae pupate within larval chambers in galls, whereas in type B galls pupation takes place between ovaries in galls or in the soil beneath the host tree. Gall midges responsible for the same general gall type are morphologically related and differ from species causing the other gall type. Phylogenetic analysis of a 410 bp fragment of the mitochondrial cytochrome b gene supports the division of the gall midge species into two groups except for D. sulcata, which appears as a subgroup of the group causing type A galls. The interspecific divergence values in group A species were between 0.5 and 3.9% with intraspecific divergence estimates of 0–0.2%. Gall midges causing type B galls had interspecific divergence values of 4.6–7.3% and intraspecific divergence values of 0–3.7%. Closely related biology and morphology together with low cytochrome b divergence estimates suggest a more recent speciation in group A when compared with species of group B. Dasineura rubiformis and D. dielsi are proposed as potential biological control agents for Acacia mearnsii De Wild. and Acacia cyclops A. Cunn. ex G. Don, respectively, in South Africa due to their narrow host range and ability to form high population densities that reduce seed formation. Both species produce galls with low biomass, which makes them comp...

No abstract