B. Dell

Nutrient uptake in mycorrhizal symbiosis

The role of mycorrhizal fungi in acquisition of mineral nutrients by host plants is examined for three groups of mycorrhizas. These are; the ectomycorrhizas (ECM), the ericoid mycorrhizas (EM), and the vesicular-arbuscular mycorrhizas (VAM). Mycorrhizal infection may affect the mineral nutrition of the host plant directly by enhancing plant growth through nutrient acquisition by the fungus, or indirectly by modifying transpiration rates and the composition of rhizosphere microflora.A capacity for the external hyphae to take up and deliver nutrients to the plant has been demonstrated for the following nutrients and mycorrhizas; P (VAM, EM, ECM), NH4+ (VAM, EM, ECM), NO3- (ECM), K (VAM, ECM), Ca (VAM, EM), SO42- (VAM), Cu (VAM), Zn (VAM) and Fe (EM). In experimental chambers, the external hyphae of VAM can deliver up to 80% of plant P, 25% of plant N, 10% of plant K, 25% of plant Zn and 60% of plant Cu. Knowledge of the role of mycorrhiza in the uptake of nutrients other than P and N is limited because definitive studies are few, especially for the ECM. Although further quantification is required, it is feasible that the external hyphae may provide a significant delivery system for N, K, Cu and Zn in addition to P in many soils. Proposals that ECM and VAM fungi contribute substantially to the Mg, B and Fe nutrition of the host plant have not been substantiated.ECM and EM fungi produce ectoenzymes which provide host plants with the potential to access organic N and P forms that are normally unavailable to VAM fungi or to non mycorrhizal roots. The relative contribution of these nutrient sources requires quantification in the field.Further basic research, including the quantification of nutrient uptake and transport by fungal hyphae in soil and regulation at the fungal-plant interface, is essential to support the selection and utilization of mycorrhizal fungi on a commercial scale.

Physiological response of plants to low boron

This review focuses on physiological responses in higher plants to B deficiency at the whole plant and organ level. Plants respond to decreasing B supply in soil solutions by slowing down or ceasing growth. Boron deficiency inhibits root elongation through limiting cell enlargement and cell division in the growing zone of root tips. In the case of severe B deficiency, the root cap, quiescent centre and protoderm of root tips disappear and root growth ceases, leading to the death of root tips. Although vascular bundles are weakly developed in B-deficient roots, early effects of B deficiency on their initiation and differentiation is poorly understood. Inhibited leaf expansion by low B indirectly decreases the photosynthetic capacity of plants, though exact roles of B in photosynthesis remain to be explored. The early inhibition of root growth, compared to shoot growth, increases the shoot:root ratio. It is hypothesised that this may enhance the susceptibility of plants to environmental stresses such as marginally deficient supplies of other nutrients and water deficit in soil.In the field, sexual reproduction is often more sensitive to low soil B than vegetative growth, and marked seed yield reductions can occur without symptoms being expressed during prior vegetative growth. In flowers, low B reduces male fertility primarily by impairing microsporogenesis and pollen tube growth. Post-fertilisation effects include impaired embryogenesis, resulting in seed abortion or the formation of incomplete or damaged embryos, and malformed fruit. However, there is a great diversity of effects of low B on reproductive growth among species, and within the same species between sites and seasons. Much of this diversity is not explained by the current literature. Key processes in reproductive development which may be impaired under B deficiency are proposed and discussed. These include the formation of a diverse array of cell wall types, the supply of carbohydrates for growth and storage reserves, and the production of flavonols. Inflorescence architecture, floral morphology, canopy structure and prevailing weather conditions are suggested as being important for xylem B delivery into flowers because of their impact on transpiration. The extent of phloem translocation of B into reproductive organs has yet to be fully assessed. The timing of B sensitive stages in reproduction of most crop plants need defining in order to facilitate appropriate timing of corrective B treatments.As most container studies have imposed B deficiency by withholding B, much of the data on severely B-deficient plants requires re-evaluation. Further studies are warranted to understand the effects of realistically low levels of B in solution on the growth of meristematic tissues and floral organs. A B-buffered solution culture system is recommended for some of this work.

Phosphorus nutrition of mycorrhizal trees.

Globally, phosphorus (P) limits productivity of trees in many forests and plantations especially in highly weathered, acidic or calcareous profiles. Most trees form mycorrhizal associations which are prevalent in the organic and mineral soil horizons. This review critically examines mechanisms that enhance the acquisition of P by tree roots. Mycorrhizal roots have a greater capacity to take up phosphate (Pi) from the soil solution than non-mycorrhizal root tips. Factors that contribute to this include the extent of extraradical hyphal penetration of soil and the physiology and biochemistry of the fungal/soil and fungal/plant interfaces. Ectomycorrhizal (ECM) trees are likely to benefit from association with basidiomycetes that possess several high-affinity Pi transporters that are expressed in extraradical hyphae and whose expression is enhanced by P deficiency. To understand fully the role of these putative transporters in the symbiosis, data regarding their localization, Pi transport capacities and regulation are required. Some ECM fungi are able to effect release of Pi from insoluble mineral P through excretion of low-molecular-weight organic anions such as oxalate, but the relative contribution of insoluble P dissolution in situ remains to be quantified. How the production of oxalate is regulated by nitrogen remains a key question to be answered. Lastly, phosphatase release from mycorrhizas is likely to play a significant role in the acquisition of Pi from labile organic forms of P (Po). As labile forms of Po can constitute the major fraction of the total P in some tropical and temperate soils, a greater understanding of the forms of Po available to the phosphatases is warranted.

Nutritive value of popular wild edible mushrooms from northern Thailand

The nutritive (and market) value of sporocarps of edible wild ectomycorrhizal fungi from northern Thailand was determined. Protein, fat, crude fibre and carbohydrate concentrations were 14.0–24.2, 2.7–9.5, 8.3–16.8, and 41.6–65.1% dry weight, respectively. Mineral contents were: macronutrients (mg/g dry wt.) P 2.1–8.1, K 12.8–45.2, S 1.1–6.1, Ca 0.1–2.4, Mg 0.5–1.6; micronutrients (mg/kg dry wt.) Fe 162–3254, Zn 37.8–253, Mn 13.0–329, Cu 11.6–81.1, B 1.6–7.1, and Se 0–12.6. The main sporocarp sugars were d-glucose, d-fructose, trehalose, d-mannose, d-arabinose, d-xylose, d-fucose, l-rhamnose, and d-galactose. The sugar alcohol components were mannitol, glycerol, myo-inositol, meso-erythritol, d-arabitol, dulcitol, xylitol, and d-sorbitol.

Plant resins—their formation, secretion and possible functions

Plant resins pose interesting ecological, taxonomic, physiological, and biochemical problems. This chapter briefly describes the resins in chemical terms and presents their contrast with certain other plant products. Resins are nonvolatile products of plants, from which they exude naturally (surface resins) or can be obtained by incision or infection (internal resins). They are insoluble in water but soluble in organic solvents. Stable, inert, and amorphous, they become sticky when heated and are fusible with no sharp melting points. They are mixtures of compounds, including flavonoids, terpenoids, and fatty substances. Resins are usually produced in specialized surface glands (glandular hairs) or internal ducts. Such ducts are widespread in certain families and occur in both woody and nonwoody plants. They are more common in gymnosperms and dicotyledons than in monocotyledons. The chapter focuses on the external resins that are secreted onto leaf surfaces, but it also provides information on resins, which remain within the plant, and other related plant products.

The diversity of ectomycorrhizal fungi associated with introduced Pinus spp. in the Southern Hemisphere, with particular reference to Western Australia

A device and method for collecting a liquid, such as urine, with little or no contamination thereof. The device when delivered for use includes a container member, an intermediate member secured to the container and a cap member encased in a closed bag and in turn secured to the intermediate member through the bag. During use the cap member is removed from the intermediate member and placed on a convenient surface, still in the closed bag. The intermediate member has a handle which then permits the user easily to hold the container in position for voiding urine into the container. The intermediate member is then removed from the container and discarded. The uncontaminated cap member is then removed from the closed bag and is threadably secured to the container so that the urine contained therein can be delivered for analysis in a substantially uncontaminated state.

Variation in Pisolithus based on basidiome and basidiospore morphology, culture characteristics and analysis of polypeptides using 1D SDS-PAGE

One hundred Pisolithus isolates, 85 Australian and 15 non-Australian collections, were compared and classified according to basidiospore and basidiome morphology, cultural characteristics and separation of polypeptides using 1D SDS-PAGE. Basidiocarps were extremely varied and 13 types were recognized ranging in size from 2 to 20 cm with various stipe types, peridium features and different coloured spore masses. Four basidiospore types were recognized within Australia. These corresponded to a large group found Australia-wide, a smaller group found throughout south-western Australia and two small groups confined to single locations. Seven culture types were described, ranging from submerged, slow growing colonies to aerial, fast growing colonies. 1D SDS-PAGE of all Pisolithus isolates identified 30 soluble polypeptides between 24 and 43 kDa that were used to group the isolates using a numerical taxonomic analysis. Basidiospore groups were readily discernible within the polypeptide groups. In addition, analysis of the polypeptide patterns alone or in combination with basidiospore and culture characteristics, resulted in groups that corresponded to host species and geographic location. These observations were further demonstrated by an ordination using the multi-dimensional scaling procedure. One cluster was composed of all the non-Australian isolates collected beneath Pinus, whilst within Australia, isolates from the eastern, southern and western seaboards fell into distinct clusters. These studies indicate that phenotypic analysis of polypeptide patterns can provide a meaningful classification system to assist in isolate selection for future experiments.

Mycosphaerella species associated with Eucalyptus in south-western Australia: new species, new records and a key

Mycosphaerella ambiphylla sp. nov. (anamorph: Phaeophleospora) and Mycosphaerella aurantia sp. nov., are described from diseased Eucalyptus globulus leaves. In addition, a new fungal record in Australia, M. mexicana, and two new records for Western Australia, M. gregaria and M. parva, are discussed. A key is provided to Mycosphaerella species on E. globulus in Western Australia.

Effects of bacteria on mycorrhizal development and growth of container grown Eucalyptus diversicolor F. Muell. seedlings

The development of ectomycorrhizas on inoculated eucalypt seedlings in commercial nurseries is often slow so that only a small percentage of roots are mycorrhizal at the time of outplanting. If mycorrhizal formation could be enhanced by co-inoculation with bacteria which promote rapid root colonisation by specific ectomycorrhizal fungi, as demonstrated by certain bacteria in the Douglas fir-Laccaria bicolor association, this would be of advantage to the eucalypt forest industry. Two bacterial isolates with a demonstrated Mycorrhization Helper Bacteria (MHB) effect on ectomycorrhiza formation between Pseudotsuga menziesii and Laccaria bicolor (S238), and seven Western Australian bacterial isolates from Laccaria fraterna sporocarps or ectomycorrhizas were tested in isolation for their effect on ectomycorrhizal development by three Laccaria spp. with Eucalyptus diversicolor seedlings. Mycorrhizal formation by L. fraterna (E710) as measured by percentage infected root tips, increased significantly (p < 0.05) by up to 296% in treatments coinoculated with MHB isolates from France (Pseudomonas fluorescens Bbc6 or Bacillus subtilis MB3), or indigenous isolates (Bacillus sp. Elf28 or a pseudomonad Elf29). In treatments coinoculated with L. laccata (E766) and the MHB isolate P. fluorescens (Bbc6) mycorrhizal development was significantly inhibited (p < 0.05). A significant Plant Growth Promoting Rhizobacteria (PGPR) effect was observed where the mean shoot d.w. of seedlings inoculated only with an unidentified bacterium (Elf21), was 49% greater than the mean of uninoculated controls (-fungus, -bacterium). Mean shoot d.w. of seedlings coinoculated with L. bicolor (S-238), which did not form ectomycorrhizas with E. diversicolor, and an unidentified bacterium (Slf14) or Bacillus sp. (Elf28) were significantly higher than uninoculated seedlings or seedlings inoculated with L. bicolor (S-238) alone. This is the first time that an MHB effect has been demonstrated in a eucalypt-ectomycorrhizal fungus association. These organisms have the potential to improve ectomycorrhizal development on eucalypts under nursery conditions and this is particularly important for fast growing eucalypt species where the retention time of seedlings in the nursery is of short duration (2–3 months).

Rapid Nitric Acid Digestion of Plant Material with an Open-Vessel Microwave System

Abstract Digestion of plant materials in hot (130–140°C) concentrated nitric acid (HNO3) is a common procedure for assessing their nutrient contents. In the conventional HNO3 digestion, desired temperatures are achieved through controlled electrical heating, and digestion occurs within Pyrex test tubes. The main limitations associated with the conventional digestion method may include (1) high labor requirement for monitoring acid levels in the tubes and digest solution transfer at the end of digestion and (2) relatively high background levels, in particular, of trace elements (e.g., Cu, B, Mn, etc.) resulting from the glass matrix or/and repeated use of digestion tubes. The availability of industrial microwave technology provides opportunities for developing improved digestion systems that overcome the above constraints while routinely processing large batches of plant samples. The present article describes a simple, reliable, and rapid digestion procedure for HNO3 with hydrogen peroxide (H2O2) digestion of plant material by using an open-vessel (50 mL polypropylene tubes with caps in which a 3.2 mm diameter ventilation hole is drilled in the center), microwave-digestion system (CEM Mars 5, manufactured by CEM Corp., USA), followed by elemental quantification using an ICP-AES. The proposed method consists of two stages: (1) the predigested (overnight) sample and HNO3 mix is heated at 75°C for 10 min, followed by 109°C for 15 min; (2) after cooling for 10 min, 1 mL of H2O2 is added to each vessel through the ventilation hole and the sample mix is heated at 109°C for a further 15 min. The analytical results were statistically analyzed by using linear regression, linear correlation, and two independent means tests to determine analytical precision and accuracy of the proposed digestion method. The results have demonstrated that this method is suitable for precise and accurate determination of macronutrients calcium (Ca), potassium (K), magnesium (Mg), phosphorus (P), sulfur (S), and micronutrients boron (B), copper (Cu), manganese (Mn), and zinc (Zn) in plant materials. The analytical variability (coefficient of variation) was mostly less than 5%, apart from that of iron (Fe) (9%). There were no significant (P ≤ 0.05) differences between the measured and certified concentrations of both macro- and micronutrients in the ASPAC and NIST1515 standard reference materials (SRM), except for Fe in NIST1515 SRM. The recovery rate of Fe in the digest solution varies with plant types, for cereal samples, higher than 90%, but for dicot species (e.g., NIST apple leaves) the recovery rate was as low as 70%. One of the important advantages of this method was the consistently (across samples and different batches) low background reading (mostly under detection limits of the ICP-AES used, for example, the concentrations of B in the blank digests were consistently less than 5 µg/L). The adoption of the present digestion method may result in time saving due to short turn-around time (less than 60 min per 50 samples) and cost saving due to low labor requirement, low acid consumption, and low-cost digestion vessels.