G. Thomson

A Signaling-Regulated, Short-Chain Dehydrogenase of Stagonospora nodorum Regulates Asexual Development

ABSTRACT The fungus Stagonospora nodorum is a causal agent of leaf and glume blotch disease of wheat. It has been previously shown that inactivation of heterotrimeric G protein signaling in Stagonospora nodorum caused development defects and reduced pathogenicity [P. S. Solomon et al., Mol. Plant-Microbe Interact. 17:456-466, 2004]. In this study, we sought to identify targets of the signaling pathway that may have contributed to phenotypic defects of the signaling mutants. A comparative analysis of Stagonospora nodorum wild-type and Gα-defective mutant (gna1) intracellular proteomes was performed via two-dimensional polyacrylamide gel electrophoresis. Several proteins showed significantly altered abundances when comparing the two strains. One such protein, the short-chain dehydrogenase Sch1, was 18-fold less abundant in the gna1 strain, implying that it is positively regulated by Gα signaling. Gene expression and transcriptional enhanced green fluorescent protein fusion analyses of Sch1 indicates strong expression during asexual development. Mutant strains of Stagonospora nodorum lacking Sch1 demonstrated poor growth on minimal media and exhibited a significant reduction in asexual sporulation on all growth media examined. Detailed histological experiments on sch1 pycnidia revealed that the gene is required for the differentiation of the subparietal layers of asexual pycnidia resulting in a significant reduction in both pycnidiospore size and numbers.

A single tube, quantitative real-time RT-PCR assay that detects four potato viruses simultaneously.

A high throughput, real-time multiplex, single tube RT-PCR assay was developed for simultaneous detection of Potato leafroll virus (PLRV), Potato virus X (PVX) and Potato virus S (PVS) in potato leaves and tubers, and Tomato spotted wilt virus (TSWV) in potato tubers and tomato leaves. The test uses four different fluorescently labelled TaqMan probes. Limits of detection sensitivity were established using a range of virus transcript copy numbers (8 x 10(1) to 8 x 10(9) copies of PVX and PVS, 1 x 10(2) to 1 x 10(10) copies of PLRV and 1 x 10(3) to 1 x 10(10) copies of TSWV). For each individual assay, the inter-assay reproducibility was high, with a coefficient of variation of the combined assays of <2%. Total RNA was extracted rapidly and efficiently from bulked samples equivalent to 300 dormant tubers to detect single infections of PLRV, PVX, PVS and TSWV simultaneously in a single assay. The multiplexed assay was validated in blind studies with leaves and tubers. This high-throughput test is accurate and sensitive, and provides seed potato industries with a cost-effective diagnostic tool to detect viruses reliably in bulked samples of dormant potato tubers.

Development and function of Pisolithus and Scleroderma ectomycorrhizas formed in vivo with Allocasuarina, Casuarina and Eucalyptus

Abstract The effect of inoculating seedlings of Eucalyptus grandis, Allocasuarina littoralis and Casuarina equisetifolia with two isolates of Pisolithus and two isolates of Scleroderma from under eucalypts was examined in a glasshouse trial. Ectomycorrhizas formed extensively on Eucalyptus (23–46% fine roots ectomycorrhizal) and Allocasuarina (18–51% fine roots ectomycorrhizal). On Casuarina, the fungi were either unable to colonize the rhizosphere (one isolate of Pisolithus), or sheathed roots, resembling ectomycorrhizas, formed on 1–2% of the fine roots. Colonization of roots by one isolate of Scleroderma resulted in the death of Casuarina seedlings. Inoculation with fungi increased shoot dry weight by up to a factor of 32 (Eucalyptus), 4 (Allocasuarina) and 3 (Casuarina). Ectomycorrhizas formed in associations with Eucalyptus and Allocasuarina had fully differentiated mantles and Hartig nets in which the host and fungal cells were linked by an extensive fibrillar matrix. Sheathed roots in Casuarina lacked a Hartig net, and the epidermis showed a hypersensitive reaction resulting in wall thickening and cell death. The sheaths are described as mantles since the density and arrangement of the hyphae in the sheaths was similar to that in mantles of the eucalypt ectomycorrhizas. The intercellular carbohydrate matrix was not produced in the Casuarina mantle in association with Pisolithus, hence the mantle was not cemented to the root. These structures differ from poorly compatible associations described previously for Pisolithus and Eucalyptus. The anatomical data indicate that ectomycorrhizal assessment based on surface morphological features may be misleading in ecological studies because compatible and incompatible associations may not be distinguishable.

Development of Proteoid Roots in Hakea obliqua R.Br. (Proteaceae) Grown in Water Culture

Proteoid roots of Hakea obliqua seedlings grow rapidly at 20°C in water culture. The surface area of an average developing proteoid root increases 1500 mm2 per day, which finally represents a 25-fold increase over that of the parent root. The epidermis and interior tissues of the rootlets are derived from the pericycle but the root cap cells originate from the endodermis of the parent root. The root cap cells of the rootlets secrete a considerable amount of mucilage both before and after emergence from the parent root.

The effects of iron ore dust on mangroves in Western Australia: Lack of evidence for stomatal damage

Anecdotal evidence suggests that iron ore dust derived from industrialshiploading activities in north-western Australia may be more injurious tomangroves than is naturally-derived dust, because of its more angularstructure and presumed ability to damage stomatal cells. Abaxial hairs onthe most common mangrove, Avicennia marina (Forfk). Vierh., havebeen thought to exacerbate this effect through trapping and retaining dust.This study examined this hypothesis. Leaves were collected from dustyindustrial areas and natural environments. Leaves in dusty environmentswere chosen on the basis of their thick coating of iron ore dust on both leafsurfaces. Approximately 3,000 stomata were examined in detail using lightmicroscopy. Hair density, stomatal aperture, cell condition and presence ofdust were also noted. Despite there often being a visible layer of dust onthe abaxial and adaxial surfaces of the leaf, evidence for dust of any kindwithin stomatal spaces was noted, in total, only three times. The lack ofvisible dust in stomata was attributed to three factors; the density andmorphology of the abaxial hairs, which prevent dust from enteringthe space between the hairs, and the improbability of dust circulating in thestagnant air within that space and moving against gravity past the guardcells. It was concluded that if iron ore dust affects mangroves, it must doso by some other mechanism, such as either increased temperature, shadingor a restriction of transpiration by the thickness of the dust on the abaxialsurface.

Glochidia ecology in wild fish populations and laboratory determination of competent host fishes for an endemic freshwater mussel of south-western Australia

Abstract. Glochidia (parasitic larvae) of freshwater mussels generally require a fish as a host. Westralunio carteri Iredale, 1934 (Bivalvia : Hyriidae), the only freshwater mussel found in south-western Australia, was listed as Vulnerable, but recently changed to Least Concern (International Union for the Conservation of Nature). Glochidia were found on four alien and seven native species of fish from 18 sites in the South West Coast Drainage Division. On alien fishes, prevalence of glochidia ranged from 0.0 to 41.0% and mean intensity (number of glochidia per infested fish) from 1.0 to 6.0, while on native fishes prevalence was 9.2–90.5% and intensity was 2.3–7.1. Glochidia infestation was greatest on benthic fishes, which may be a consequence of greater encounter rates, but other factors, such as host size, probably also influence glochidia prevalence and intensity. Glochidia were generally restricted to fins of infested fish, and were rarely on gills or the body surface. In the laboratory, four native and one alien fish species were found to be competent hosts for their ability to produce juvenile W. carteri, but two alien fish species were not. The inability of some alien fishes to produce juvenile W. carteri could potentially reduce recruitment success in areas dominated by alien fishes.

Identifying abnormalities in symbiotic development between Trifolium spp. and Rhizobium leguminosarum bv. trifolii leading to sub-optimal and ineffective nodule phenotypes

BACKGROUND AND AIMS Legumes overcome nitrogen limitations by entering into a mutualistic symbiosis with N(2)-fixing bacteria (rhizobia). Fully compatible associations (effective) between Trifolium spp. and Rhizobium leguminosarum bv. trifolii result from successful recognition of symbiotic partners in the rhizosphere, root hair infection and the formation of nodules where N(2)-fixing bacteroids reside. Poorly compatible associations can result in root nodule formation with minimal (sub-optimal) or no (ineffective) N(2)-fixation. Despite the abundance and persistence of strains in agricultural soils which are poorly compatible with the commercially grown clover species, little is known of how and why they fail symbiotically. The aims of this research were to determine the morphological aberrations occurring in sub-optimal and ineffective clover nodules and to determine whether reduced bacteroid numbers or reduced N(2)-fixing activity is the main cause for the Sub-optimal phenotype. METHODS Symbiotic effectiveness of four Trifolium hosts with each of four R. leguminosarum bv. trifolii strains was assessed by analysis of plant yields and nitrogen content; nodule yields, abundance, morphology and internal structure; and bacteroid cytology, quantity and activity. KEY RESULTS Effective nodules (Nodule Function 83-100 %) contained four developmental zones and N(2)-fixing bacteroids. In contrast, Sub-optimal nodules of the same age (Nodule Function 24-57 %) carried prematurely senescing bacteroids and a small bacteroid pool resulting in reduced shoot N. Ineffective-differentiated nodules carried bacteroids aborted at stage 2 or 3 in differentiation. In contrast, bacteroids were not observed in Ineffective-vegetative nodules despite the presence of bacteria within infection threads. CONCLUSIONS Three major responses to N(2)-fixation incompatibility between Trifolium spp. and R. l. trifolii strains were found: failed bacterial endocytosis from infection threads into plant cortical cells, bacteroid differentiation aborted prematurely, and a reduced pool of functional bacteroids which underwent premature senescence. We discuss possible underlying genetic causes of these developmental abnormalities and consider impacts on N(2)-fixation of clovers.

Distribution of Protein Bodies and Phytate-Rich Inclusions in Grain Tissues of Low and High Iron Rice Genotypes

The present study aims to understand whether genotypic differences in grain iron (Fe) concentration in four rice genotypes are related to its association with protein bodies containing phytate-rich inclusions. Rice genotypes with high and low grain Fe concentrations in unpolished brown rice were grown in a greenhouse at Chiang Mai, Thailand, and grains were harvested at maturity. The presence of protein bodies and phytate-rich inclusions in rice grain tissues were examined by means of light and transmission electron microscopy (TEM). The composition of mineral elements in different grain tissues was examined using energy dispersive X-ray microanalysis (EDX) and chemical analysis. The relative distribution pattern of protein bodies in the tissues was similar among the four rice genotypes, which resembled the pattern of grain N concentrations in these tissues. The high grain Fe genotypes (based on brown rice Fe concentration) had more protein bodies containing phytate-rich inclusions in the embryo and aleurone layer tissues than the low Fe genotypes. Phytate-rich inclusions were not detected in the endosperm tissues in all genotypes. In conclusion, the presence of protein bodies with phytate-rich inclusions predominantly in the embryo and aleurone regions of the grain is an important parameter contributing to the variation in brown rice Fe concentration among the genotypes, but not in the white rice (the endosperm). Iron associated with the phytate-rich inclusions present in the embryo and aleurone layer tissues are largely lost during the polishing process to produce white rice.

Uneven Distribution of Zinc in the Dorsal and Ventral Sections of Rice Grain

ABSTRACT This study examined the distribution of zinc in dorsal and ventral grain sections of rice varieties with low (RD21), moderate (CNT1 and KDML105), and high (KPK and NR) zinc concentrations. Samples of unhusked rice grain were partitioned longitudinally and analyzed for zinc. The concentration of zinc was higher in the dorsal grain section than the ventral section, but to a different extent in different varieties. In unpolished rice, the zinc concentration in the dorsal section exceeded that in the ventral section by 14% in CNT1 to 63% in RD21. The higher zinc concentration in the dorsal section of unpolished rice might be explained by storage in the multiple cell layered aleurone and thicker pericarp. The higher concentration of dorsal zinc, however, was maintained after polishing, irrespective of the removal of grain surface by polishing that varied with variety and polishing time from 11 to 207 μm in depth. Zinc concentration of polished rice, ranging from 14 to 28 mg of zinc/kg, was strongly pr...

Anther diversity and function in Verticordia DC. (Myrtaceae)

Anther form and structure across the taxonomic groups inVerticordia were examined. The three anther types which were recognised — rectangular, oblong and saccate, accord well with the three subgenera into which the genus has been divided. The sporogenous part of the anther has a fairly typical angiosperm anatomy. However in many species there is a small or large gland in the upper filament/connective which contains lipidic contents. The anatomy of this structure is based on that of the oil glands which are ubiquitous in Myrtaceae primary tissues. However the gland is usually much larger than these and is schizolysigenous in origin. Evolutionary development of the anthers in the genus is related to pollination systems and the development of secondary pollen presentation from the upper style in some groups. Anther glands may have originally had a protective function for the sporogenous tissue. However in different groups the function has changed or the gland has disappeared. In some species in subgenusChrysoma (which does not have secondary pollen presentation) the gland contents seem to be an additional food source for pollinators. In other groups, with the development of secondary pollen presentation the protective function has become redundant and anther glands have either disappeared or produce contents which have become part of the process of pollen dispersal.