Keitaro Tawaraya

Arbuscular mycorrhizal dependency of different plant species and cultivars

Abstract The degree of plant growth change associated with arbuscular mycorrhizal (AM) colonization is expressed as mycorrhizal dependency (MD). In this review, previous reports on the differences in MD among plant species or cultivars were surveyed, and the factors affecting the differences are discussed. Mean values of MD were 44% for field crops (37 species), 56% for forage crops (46 species), 70% for wild grasses and forbs (140 species), 79% for trees (26 species), and 56% for all plants (250 species), indicating that the cultivated plant species showed a lower MD than the wild plant species. MD was negatively correlated with root morphological characteristics such as root length, root dry weight, root hair length, density of root hairs, the ability of roots to acquire phosphate from soil, and the phosphorus utilization efficiency of the host plant. Inoculation of arbuscular mycorrhizal fungi (AMF) for low input systems should be carried out in considering differences in MD.

The plasma membrane strength of the root-tip cells and root phenolic compounds are correlated with Al tolerance in several common woody plants

Abstract Ten species including one cultivar of common woody plants, i.e., Picea abies Karst. (Norway spruce), Gleditsia triacanthos L. (honey locust), Robinia pseudoacacia L. (black locust), Populus tremuloides Michx. (quaking aspen), Eucalyptus viminalis Labill. (eucalyptus), Cryptomeria japonica (Japanese cedar), Camellia sinensis L., cv. Yabukita (tea), Rhus succedanea L. (sumac), Pinus densiflora (Japanese red pine), and Pinus thunbergii Parl., cv. Sanshu (Sanshu black pine), and 2 species of marker crop plants, i.e., Oryza sativa L., cv. Sasanishiki (rice) and Hordeum vulgare L., cv. Manriki (barley), were cultured for 38 d at pH 4.3 in full nutrient solutions under three different stress conditions; 1) high AI, low P and low pH (combined stress), 2) low P and low pH, and 3) control. Soluble ionic Al and P concentrations in the media were maintained at almost 55 and 7 µM, respectively. P. thunbergii cv. Sanshu, C. sinensis, G. triacanthos, R. pseudoacacia, P. abies, and C. japonica were more tolerant to the combined stress than Oryza sativa known to be one of the most tolerant crop plants. Al tolerance obtained after the short-term stress for 24 h in CaCl2 solution at pH 4.7 was positively correlated with that obtained after the long-term combined stress, suggesting that a short-term screening technique can be used for the estimation of tolerance in acid soils. Under the combined stress conditions, low P stress was not expressed in any plant parts, Al stress was expressed primarily in roots and low pH stress was highly expressed in shoots. The roots of the AI-tolerant plants contained a significantly lower amount of Al with a higher K accumulation ratio. The plasma membrane strength (PMS), corresponding to the intactness of the PM permeability of root-tip cells during the re-elongation period without Al after temporary treatment with AI, was correlated with Al tolerance. Positive correlation between low pH tolerance and Al tolerance at pH 4.7 without H+ toxicity in both short-term experiments suggested that the PM of the root-tip cells was a common target for both stresses. Al tolerance of woody plants was positively correlated with the concentration of soluble phenolic compounds in roots irrespective of the treatment, but not with exuded phenolic compounds. In contrast to acidic conditions, in vitro binding affinity to Al ions at pH 7.0 was significantly higher at equimolar concentrations of quercetin, catechin, and chlorogenic acid but lower in the case of rutin, citric, oxalic, and malic acids. To our knowledge, this is the first report in which phenolic compounds in roots were quantitatively related to Al tolerance in woody plants. It was eventually suggested that AI-tolerant woody plants constitutively adopted a dual strategy involving a superior PMS and a higher amount of root phenolic compounds which can bind strongly with and detoxify Al ions in the cytoplasm.

Effect of onion (Allium cepa) root exudates on the hyphal growth of Gigaspora margarita

Abstract The effect of root exudates from onions differing in P status on spore germination and hyphal growth of arbuscular mycorrhizal fungi was investigated. Onion (Allium cepa) was grown in solution culture at different phosphorus concentrations (0, 0.1, 1.0, 8.0 and 24.0 mg P l–1) and root exudates were collected. When spores of the arbuscular mycorrhizal fungus, Gigaspora margarita were incubated with these root exudates, spore germination was only slightly affected but hyphal growth was greatly affected, particularly with exudates from P-deficient plants. This suggests that the P nutrition of host plants influences the composition of root exudates and thereby the hyphal growth of arbuscular mycorrhizal fungi.

Effect of root exudate fractions from P-deficient and P-sufficient onion plants on root colonisation by the arbuscular mycorrhizal fungus Gigaspora margarita

Abstract The effect of root exudates from P-deficient onion on root colonisation by an arbuscular mycorrhizal fungus was examined. Onions (Allium cepa L.) were grown in solution culture at phosphorus concentrations of 0 (P0) and 2 (P2) mg P l–1. Root exudates were collected and fractionated with Amberlite XAD-4 resin to give EtOH and water soluble fractions. Onions inoculated with the arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall were grown with or without (control) root exudates and exudate fractions in a growth chamber. After 24 days, arbuscular mycorrhiza levels and appressoria formation had increased in plants treated with P0-root exudate or the P0-EtOH fraction when compared to corresponding P2 treatments or control plants. P0 and P2 water-soluble fractions did not significantly affect either aspect of fungal development. These results suggest that hydrophobic compounds found in root exudates from P-deficient onion increase appressorium formation and, therefore, enhance mycorrhiza development.

Solubilization of Insoluble Inorganic Phosphate by Hyphal Exudates of Arbuscular Mycorrhizal Fungi

ABSTRACT Increased phosphate (P) uptake in plants by arbuscular mycorrhizal (AM) fungi is thought to depend mainly on the extension of external hyphae into soil. On the other hand, it is known that the hyphae of some kinds of ectomycorrhizal fungi release organic acids into soil and that they dissolve the insoluble inorganic P. This study collected hyphal exudates of AM fungi within compartmentalized pot culture and clarified their ability to solubilize insoluble inorganic P. Sterilized Andisol was packed in pots that were separated into root and hyphal compartments with a nylon net of 30 μm pore size. Seedlings of Allium cepa inoculated with AM fungi, Gigaspora margarita, or Glomus etunicatum were grown. Control pots were not inoculated. Mullite ceramic tubes were buried in the soil of each compartment and soil solution was collected. The anionic fraction of the soil solution was incubated with iron phosphate (4 mg FePO4 in 1 mL of 0.4 acetate buffer). Solubilized P was measured. The AM colonization of plants inoculated with G. margarita and G. etunicatum was 86% and 54%, respectively. Adhesion of external hyphae was observed on the surface of the mullite ceramic tubes buried in soil of the hyphal compartment. Colonization of both fungi increased shoot P uptake and growth. Soil solution collected from the hyphal compartments of both fungi solubilized more P than did that from uninoculated plants. It is suggested that hyphal exudates can contribute to increased P uptake of colonized plants.

Arbuscular mycorrhizal colonization of tree species grown in peat swamp forests of Central Kalimantan, Indonesia

Abstract Arbuscular mycorrhizas improve the growth and nutrient uptake of plants and are formed in 80% of all land plants. Little information is available on the status of arbuscular mycorrhizas in tropical soils. The objective of this study was to clarify mycorrhizal colonization of tree species grown in tropical peat soils. Seedlings of 22 tree species in 14 families grown in a peat swamp forest of Central Kalimantan, Indonesia were collected in 2000 and 2001. Roots were stained with 0.05% aniline blue and arbuscules, vesicles and internal hyphae were observed under a compound microscope. Seventeen of 22 species showed arbuscular mycorrhizal colonization. Arbuscular mycorrhizal colonization was observed for the first time in roots of Shorea teysmanniana, Shorea balangeran, Shorea uliginosa (Dipterocarpaceae), Calophyllum sclerophyllum, Calophyllum soulattri (Guttiferae), Cratoxylum arborescens (Guttiferae), Tetramerista glabra (Tetrameristaceae), Palaquium gutta (Sapotaceae), Melastoma melabathricum (Melastomataceae), Gonystylus bancanus (Thymelaeaceae), Hevea brasiliensis (Euphorbiaceae) and Campnosperma auriculatum (Anacardiaceae). C. soulattri, C. arborescens, G. bancanus, Acacia mangium, M. melabathricum and H. brasiliensis showed a percentage mycorrhizal colonization of 50% or higher. No arbuscular mycorrhizal colonization was found in Hopea mengarawan (Dipterocarpaceae), Koompassia malacensis (Caesalpiniaceae), Tristaniopsis whiteana (Myrtaceae), Combretocapus rotundatus (Rhizophoraceae) and Dyera costulata (Apocynaceae). It is suggested that inoculation of arbuscular mycorrhizal fungi can improve the early growth of some tree species grown in peat swamp forests and this will be expected as a key technology to rehabilitate disturbed peatlands.

Inoculation with the ectomycorrhizal fungi Pisolithus arhizus and Scleroderma sp. improves early growth of Shorea pinanga nursery seedlings

Abstract.Trees of the family Dipterocarpaceae are the dominant trees in Southeast Asian tropical forests where they play an important ecological role and are also important commercially. An experiment was conducted to determine the effect of ectomycorrhizal fungi on the growth of dipterocarp species in peat soils. Seedlings of Shorea pinanga were inoculated with spores of two ectomycorrhizal fungi, Pisolithus arhizus and Scleroderma sp. were grown in pots containing sterilized peat soil for 7 months. The percentage of ectomycorrhizal colonization on S. pinanga exceeded 86%. Colonization of S. pinanga roots by ectomycorrhizal fungi resulted in increased shoot height, stem diameter, number of leaves, and shoot fresh and dry weight. Survival rates of S. pinanga were greater for inoculated seedlings than control seedlings. These results suggest that inoculation of ectomycorrhizal fungi can improve the early growth of S. pinanga grown in tropical forests and that this technique will accelerate the rehabilitation of degraded dipterocarp forests.

The plasma membrane intactness of root-tip cells is a primary factor for Al-tolerance in cultivars of five species

Abstract We investigated the role of the cell wall and plasma membrane (PM) of root-tip cells in Al tolerance in Al-tolerant and Al-sensitive cultivars of five plant species (rice, maize, pea, wheat, and sorghum). No correlation was found between the differences in Al tolerance and the cation exchange capacity of cell walls isolated from root-tips (0–1 em). Preliminary exposure to Al for 1 h was sufficient to inhibit subsequent root re-elongation in an Al-free solution, and the inhibitory effect was more pronounced in the Al-sensitive cultivars than in the Al-tolerant ones. Together with the inhibition of root re-elongation, the PM of the root-tip cells of all the Al-sensitive cultivars was more permeabilized than that of the Al-tolerant cultivars, based on the FDA-PI fluorescence staining technique. Exposure for 30 min to Al treatment at 100 µM significantly increased the PM permeability of protoplasts isolated from the root-tips for the Al-sensitive pea cultivar placed in a moderately hypotonic medium. Protoplasts from root-tip portions of all the Al-sensitive cultivars took up more Al than those of the Al-tolerant ones when treated with 100 pM Al under isotonic conditions for 30 min. The co-existence of DNP or hypotonic conditions led to a larger increase of Al uptake by the protoplasts from Al-sensitive maize cultivars. These results suggest that Al ions rapidly alter the PM of the root-tip portion in the Al-sensitive cultivars, irrespective of plant species, resulting in an increase of the PM permeability.

Arbuscular mycorrhizal colonization in Lupinus and related genera

Abstract Lupinus and related genera were investigated in order to determine why arbuscular mycorrhizal fungi do not colonize non-host plants. Thirty-six plant species of Lupinus and ten plant species in seven related genera were inoculated with arbuscular mycorrhizal fungi, Gigaspora margarita and Glomus mosseae. The mycorrhizal colonization and growth of these plants were examined at 50 to 89 d after inoculation. No arbuscule formation was observed in any of the Lupinus species. Growth of external hyphae was observed in thirty-three species of Lupinus, vesicles were observed in two species and internal hyphae were observed in eight species. All ten plant species belonging to related genera were colonized with mycorrhizal fungi. These results suggest that only Lupinus in the tribe Genisteae, family Leguminosae is a non-host plant for arbuscular mycorrhizal symbiosis.

Importance of root length in mycorrhizal colonization of welsh onion

Abstract Sixteen cultivars of Welsh onion (Allium fistulosum L.) with different root lengths were evaluated for phosphorus (P) uptake and response to arbuscular mycorrhizal inoculation. Allium fistulosum were grown with or without (control) arbuscular mycorrhizal fungus Glomus fasciculatum. Mycorrhizal colonization, root length, shoot dry weight and shoot P concentration were determined 82 d after sowing. All cultivars were highly colonized with G. fasciculatum. Shoot P uptake and shoot dry weight were different among cultivars and increased by the mycorrhizal colonization. Cultivars with short roots were more responsive to the mycorrhizal colonization than those with long roots. This suggests that root length should be considered in mycorrhizal‐plant symbiosis.