Effects of seed bank disturbance on the fine-scale genetic structure of populations of the rare shrub Grevillea macleayana.
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Dispersal in most plants is mediated by the movement of seeds and pollen, which move genes across the landscape differently. Grevillea macleayana is a rare, fire-dependent Australian shrub with large seeds lacking adaptations for dispersal; yet it produces inflorescences adapted to pollination by highly mobile vertebrates (eg birds). Interpreting fine-scale genetic structure in the light of these two processes is confounded by the recent imposition of anthropogenic disturbances with potentially contrasting genetic consequences: (1) the unusual foraging behaviour of exotic honeybees and 2. widespread disturbance of the soil-stored seedbank by road building and quarrying. To test for evidence of fine-scale genetic structure within G. macleayana populations and to test the prediction that such structure might be masked by disturbance of the seed bank, we sampled two sites in undisturbed habitat and compared their genetic structure with two sites that had been strongly affected by road building using a test for spatial autocorrelation of genotypes. High selfing levels inferred from genotypes at all four sites implies that pollen dispersal is limited. Consistent with this, we observed substantial spatial clustering of genes at 10 m or less in the two undisturbed populations and argue that this reflects the predicted effects of both high selfing levels and limited seed dispersal. In contrast, at the two sites disturbed by road building, spatial autocorrelation was weak. This suggests there has been mixing of the seed bank, counteracting the naturally low dispersal and elevated selfing due to honeybees. Pollination between near neighbours with reduced relatedness potentially has fitness consequences for G. macleayana in disturbed sites. (+info)
Fast pollen tube growth in Conospermum species.
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BACKGROUND AND AIMS: An unusual form of pollen tube growth was observed for several Conospermum species (family Proteaceae). The rate of pollen tube growth, the number of tubes to emerge and the ultrastructure of these tubes are given here. METHODS: Pollen was germinated in vitro in different sucrose concentrations and in the presence of calcium channel blockers, and tube emergence and growth were recorded on a VCR. Measurements were taken of the number of tubes to emerge and rate of tube emergence. Pollen behaviour in vivo was also observed. The ultrastructure of germinated and ungerminated pollen was observed using TEM. RESULTS: After 10 s to 3 min in germination medium, up to three pollen tubes emerged and grew at rates of up to 55 micro m s(-1); the rate then slowed to around 2 micro m s(-1), 30 s after the initial growth spurt. Tubes were observed to grow in pulses, and the pulsed growth continued in the presence of calcium channel blockers. Optimal sugar concentration for pollen germination was 300 g L(-1), in which up to 81 % of pollen grains showed fast germination. Germination and emergence of multiple tubes were observed in sucrose concentrations of 100-800 g L(-1). The vegetative and generative nuclei moved into one of the tubes. Multiple tubes from a single grain were observed on the stigma. Under light microscopy, the cytoplasm in the tube showed a clear region at the tip. The ultrastructure of C. amoenum pollen showed a bilayered exine, with the intine being very thick at the pores, and elsewhere having large intrusions into the plasma membrane. The cytoplasm was dense with vesicles packed with inner tube cell wall material. Golgi apparatus producing secretory vesicles, and mitochondria were found throughout the tube. The tube wall was bilayered; both layers being fibrous and loosely packed. CONCLUSIONS: It is proposed that, for Conospermum, initial pollen tube wall constituents are manufactured and stored prior to pollen germination, and that tube extension occurs as described in the literature for other species, but at an exceptionally fast rate. (+info)
Evidence for ancient genetic subdivision among recently fragmented populations of the endangered shrub Grevillea caleyi (Proteaceae).
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The genetic effects of population fragmentation cannot be interpreted without understanding the underlying pattern of genetic variation resulting from historic population processes. We used AFLP markers to determine genetic structure and distribution of genetic diversity among populations of an endangered Australian shrub Grevillea caleyi (Proteaceae). Populations that occurred historically on four ridges have new been fragmented to varying degrees, producing some large, relatively pristine populations and very small populations consisting of fewer than 10 adult plants. We found marked population genetic structure (65.9% of genetic variation was among populations) and a significant relationship between genetic and geographic distance (rm=0.564, P=0.004). However, only 14% of overall genetic differentiation was attributable to variation among ridges, compared with 52% among populations within ridges. Moreover, genetic diversity within samples of plants did not vary with either population size or degree of isolation. Thus, the present genetic structure of populations is probably almost entirely the product of historical events. Fine-scale structuring within populations prior to fragmentation may have been caused by limited seed and pollen dispersal, despite a complex suite of (mostly avian) pollinators, and a mixed mating system that allows a large amount of selfing. The combined effects of adult longevity and a soil-stored seed bank may have buffered the recently fragmented populations against the effects of dramatic reductions in numbers of adult plants. (+info)
Tissue and cellular phosphorus storage during development of phosphorus toxicity in Hakea prostrata (Proteaceae).
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Storage of phosphorus (P) in stem tissue is important in Mediterranean Proteaceae, because proteoid root growth and P uptake is greatest during winter, whereas shoot growth occurs mostly in summer. This has prompted the present investigation of the P distribution amongst roots, stems, and leaves of Hakea prostrata R.Br. (Proteaceae) when grown in nutrient solutions at ten P-supply rates. Glasshouse experiments were carried out during both winter and summer months. For plants grown in the low-P range (0, 0.3, 1.2, 3.0, or 6.0 micromol d(-1)) the root [P] was > stem and leaf [P]. In contrast, leaf [P] > stem and root [P] for plants grown in the high-P range (6.0, 30, 60, 150, or 300 micromol P d(-1)). At the highest P-supply rates, the capacity for P storage in stems and roots appears to have been exceeded, and leaf [P] thereafter increased dramatically to approximately 10 mg P g(-1) dry mass. This high leaf [P] was coincident with foliar symptoms of P toxicity which were similar to those described for many other species, including non-Proteaceae. The published values (tissue [P]) at which P toxicity occurs in a range of species are summarized. X-ray microanalysis of frozen, full-hydrated leaves revealed that the [P] in vacuoles of epidermal, palisade and bundle-sheath cells were in the mM range when plants were grown at low P-supply, even though very low leaf [P] was measured in bulk leaf samples. At higher P-supply rates, P accumulated in vacuoles of palisade cells which were associated with decreased photosynthetic rates. (+info)
Developmental physiology of cluster-root carboxylate synthesis and exudation in harsh hakea. Expression of phosphoenolpyruvate carboxylase and the alternative oxidase.
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Harsh hakea (Hakea prostrata R.Br.) is a member of the Proteaceae family, which is highly represented on the extremely nutrient-impoverished soils in southwest Australia. When phosphorus is limiting, harsh hakea develops proteoid or cluster roots that release carboxylates that mobilize sparingly soluble phosphate in the rhizosphere. To investigate the physiology underlying the synthesis and exudation of carboxylates from cluster roots in Proteaceae, we measured O2 consumption, CO2 release, internal carboxylate concentrations and carboxylate exudation, and the abundance of the enzymes phosphoenolpyruvate carboxylase and alternative oxidase (AOX) over a 3-week time course of cluster-root development. Peak rates of citrate and malate exudation were observed from 12- to 13-d-old cluster roots, preceded by a reduction in cluster-root total protein levels and a reduced rate of O2 consumption. In harsh hakea, phosphoenolpyruvate carboxylase expression was relatively constant in cluster roots, regardless of developmental stage. During cluster-root maturation, however, the expression of AOX protein increased prior to the time when citrate and malate exudation peaked. This increase in AOX protein levels is presumably needed to allow a greater flow of electrons through the mitochondrial electron transport chain in the absence of rapid ATP turnover. Citrate and isocitrate synthesis and accumulation contributed in a major way to the subsequent burst of citrate and malate exudation. Phosphorus accumulated by harsh hakea cluster roots was remobilized during senescence as part of their efficient P cycling strategy for growth on nutrient impoverished soils. (+info)
New endophytic isolates of Muscodor albus, a volatile-antibiotic-producing fungus.
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Muscodor albus, an endophytic fungus originally isolated from Cinnamomum zeylanicum, produces a mixture of volatile organic compounds (VOCs) in culture and its spectrum of antimicrobial activity is broad. Using the original isolate of M. albus as a selection tool, it has been possible to find other culturally and biochemically unique wild-type isolates of this organism existing as endophytes in a variety of other plant species, including Grevillea pterifolia (fern-leafed grevillea), Kennedia nigriscans (snake vine) and Terminalia prostrata (nanka bakarra) growing in the northern reaches of the Northern Territory of Australia. Interestingly, none of the new isolates had a culture morphology that was identical to the original isolate, nevertheless each possessed hyphal characteristics that resembled that isolate. Furthermore, their ITS-5.8S rDNA sequences were 96-99 % identical to that of M. albus and the isolates were considered M. albus on the basis of the DNA sequence data. However, the VOCs produced by these new isolates greatly differed in quality from the original strain by virtue of the production of naphthalene, naphthalene, 1,1'-oxybis-, and one or more other compounds. In bioassays with a range of test micro-organisms, including fungi and bacteria, each isolate possessed biological activity but the range of activity was great. Artificial mixtures of some of the VOCs mimicked the effects of the VOCs of the fungus. The value of these observations to the biology and practical uses of M. albus in agriculture and other applications is discussed. (+info)
Effects of three nickel salts on germinating seeds of Grevillea exul var. rubiginosa, an endemic serpentine Proteaceae.
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BACKGROUND AND AIMS: Serpentine soils are usually quite infertile, arid and toxic, mainly because they contain high levels of heavy metals such as Ni. The aim of the present work was to assess the effects of Ni on the germinating seeds of Grevillea exul var. rubiginosa, an endemic serpentine Proteaceae of New Caledonia. In addition, the distribution of macronutrients and the Ni levels in germinating seeds were examined. METHODS: Seeds were sown in glass Petri dishes and exposed to increasing concentrations of Ni (5 to 500 mg Ni L(-1)) using Ni chloride, Ni sulphate and Ni acetate. The germination percentage and root length were measured after 40 d. Longitudinal frozen sections of germinating seeds growing in the presence of Ni (500 mg L(-1) for all three salts) were used for X-ray microanalysis and X-ray elemental mapping using scanning electron microscopy (SEM). KEY RESULTS: Ni chloride resulted in the greatest reductions in germination and root growth, particularly at 500 mg L(-1), followed by Ni sulphate and Ni acetate. SEM images revealed Ca crystalline structures in the seed coat for all the samples. S/Ca and Mg/P/K/Mn were found to be distributed differently in Ni-treated samples, whereas they all followed the same pattern in the controls. For all three salts, the Ni added to the medium had accumulated in the seed coat, whereas the endosperm seemed to be devoid of Ni. CONCLUSIONS: It is assumed that the seed coat is able to reduce the amount of Ni entering the seed, and that a high level of Ni induced the mobilization of macronutrients. (+info)
Molecular variation and fingerprinting of Leucadendron cultivars (Proteaceae) by ISSR markers.
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BACKGROUND AND AIMS: There are more than 80 species of Leucadendron and most are used as cut flowers. Currently, more than 100 cultivars are used by industry and many of them are interspecific hybrids. The origin of most cultivars is unclear and their genetic diversity and relationships have not been studied. This investigation was carried out to evaluate the genetic variation and relationships among 30 Leucadendron cultivars. METHODS: ISSR markers were applied to determine the genetic variation and to discriminate Leucadendron cultivars. Sixty-four ISSR primers were screened and 25 primers were selected for their ability to produce clear and reproducible patterns of multiple bands. KEY RESULTS: A total of 584 bands of 305-2400 bp were amplified, of which 97 % were polymorphic. A dendrogram generated using the Unweighted Pair Group Method with Arithmetic Average based on a distance measure of total character difference showed that the Leucadendron cultivars clustered into two main groups. Twenty-four of the 30 cultivars can be unequivocally differentiated, but identical profiles were observed for three cultivar pairs, 'Katie's Blush' and 'Silvan Red', 'Highlights' and 'Maui Sunset', and 'Yellow Crest' and 'Yellow Devil'. CONCLUSIONS: ISSR profiling is a powerful method for the identification and molecular classification of Leucadendron cultivars. A fingerprinting key was generated based on the banding patterns produced using two ISSR primers (UBC856 and UBC857). In addition cultivar-specific ISSR bands were obtained for 17 of the 30 Leucadendron cultivars tested. (+info)