Lack of arginine- and polyphosphate-storage pools in a vacuole-deficient mutant (end1) of Saccharomyces cerevisiae

AbstractYeast cells accumulate large amounts of arginine and polyphosphate in their vacuoles and utilize these compounds as endogenous nitrogen or phosphate sources under conditions of starvation. We examined a vacuoleless mutant, end1, and found that it stored virtually no arginine or polyphosphate when grown on a medium with arginine as the sole nitrogen source. When starved of nitrogen or phosphate it stopped growing much faster than the wildtype. Unlike the wildtype, end1 showed no accumulation of polyphosphate and, concomitantly, of arginine after a period of phosphate starvation. The results support the concept that vacuoles contain the main reserves of nitrogen and phosphate in fungi

Molecular identification of arbuscular mycorrhizal fungi in roots: Perspectives and problems

Molecular identification methods are about to revolutionize studies on ecology of arbuscular mycorrhiza. These techniques offer the unique opportunity to investigate communities of arbuscular mycorrhizal fungi (AMF) within roots. Recent technical advances are reviewed, discussing their drawbacks and advantages. An experimental approach to analyze AMF communities within roots using a molecular identification method is presented. Sample results from the analysis of trap cultures from a current project are show

The cultivation bias: different communities of arbuscular mycorrhizal fungi detected in roots from the field, from bait plants transplanted to the field, and from a greenhouse trap experiment

The community composition of arbuscular mycorrhizal fungi (AMF) was investigated in roots of four different plant species (Inula salicina, Medicago sativa, Origanum vulgare, and Bromus erectus) sampled in (1) a plant species-rich calcareous grassland, (2) a bait plant bioassay conducted directly in that grassland, and (3) a greenhouse trap experiment using soil and a transplanted whole plant from that grassland as inoculum. Roots were analyzed by AMF-specific nested polymerase chain reaction, restriction fragment length polymorphism screening, and sequence analyses of rDNA small subunit and internal transcribed spacer regions. The AMF sequences were analyzed phylogenetically and used to define monophyletic phylotypes. Overall, 16 phylotypes from several lineages of AMF were detected. The community composition was strongly influenced by the experimental approach, with additional influence of cultivation duration, substrate, and host plant species in some experiments. Some fungal phylotypes, e.g., GLOM-A3 (Glomus mosseae) and several members of Glomus group B, appeared predominantly in the greenhouse experiment or in bait plants. Thus, these phylotypes can be considered r strategists, rapidly colonizing uncolonized ruderal habitats in early successional stages of the fungal community. In the greenhouse experiment, for instance, G. mosseae was abundant after 3months, but could not be detected anymore after 10months. In contrast, other phylotypes as GLOM-A17 (G. badium) and GLOM-A16 were detected almost exclusively in roots sampled from plants naturally growing in the grassland or from bait plants exposed in the field, indicating that they preferentially occur in late successional stages of fungal communities and thus represent the K strategy. The only phylotype found with high frequency in all three experimental approaches was GLOM A-1 (G. intraradices), which is known to be a generalist. These results indicate that, in greenhouse trap experiments, it is difficult to establish a root-colonizing AMF community reflecting the diversity of these fungi in the field roots because fungal succession in such artificial systems may bias the results. However, the field bait plant approach might be a convenient way to study the influence of different environmental factors on AMF community composition directly under the field conditions. For a better understanding of the dynamics of AMF communities, it will be necessary to classify AMF phylotypes and species according to their life history strategie

Genotype x Environment Interactions of Winter Wheat

Winter wheat cultivars for organic farming have to be adapted to highly variable environments. Yield and yield stability, the nutritional value and the bread making quality are here of major importance. Particularly, seed quality, tillering capacity, regeneration ability after harrowing, weed suppression ability, resistance or tolerance against diseases and improved nutrient use efficiency (NUE) under limited nutrient conditions need to be improved by specific breeding efforts (Kunz et al., 2006; Löschenberger et al., 2008). Ten winter wheat cultivars were grown in 2007 in two organic systems of the DOK long-term experiment in CH-Therwil. Eight of these cultivars were tested in 2008 at three organic farms in different pedo-climatic environments in Switzerland to observe genotype x environment interactions under different organic conditions. In contrast to the DOK site on a fertile loess soil, the on-farm sites were located on sandy or sandy-loamy sites with lower inherent yield potential. We assessed grain yield, yield components and parameters related to baking quality and NUE. Grain yield at the on-farm sites ranged between 2.2 t ha-1 and 2.8 t ha-1 and was much lower than at the DOK sites ( 3.7 t ha-1 to 4.2 t ha-1) (Hildermann et al., 2009). Cultivars and sites significantly affected grain yield. Genotype x environment interactions were significant across the three on-farm sites; however they were not significant across all five organically managed sites. Calculated across the on farm sites, there was a tendency towards higher yields of the organically bred cultivars. This effect was statistically significant at the lowest yielding site, where yield of the organically bred cultivars was 14% higher than yields of the conventionally bred cultivars. However, at the DOK sites and averaged across all five organic sites, the organically bred cultivars could not outperform the conventionally bred cultivars. Similar to the grain yield, the total gluten content increased from the on-farm sites to the DOK sites. Irrespective of the site, the gluten index of the cultivars Scaro, Antonius and Caphorn was stable. In contrast, the gluten index of the cultivars Sandomir, CCP and Titlis highly varied between the tested environments. Yield was significantly correlated with grain N yield (r = 0.93) and nitrogen (N) utilization efficiency (NUtE) (r = 0.72). Genotype x environment interactions were not significant for grain N yield, however strongly significant for NUtE (p < 0.01). The conventionally bred cultivars strongly responded to environmental conditions and showed a low NUtE under at low N supply. In contrast, NUtE of the organically bred cultivars Scaro and Sandomir was stable across all test environments. Beside high yields, cultivars suitable for organic farming should achieve high baking quality and nutrient use efficiency under nutrient limited conditions. Among the tested cultivars, the organically bred cultivar Scaro revealed such a performance across all tested sites

Regulation of plants’ phosphate uptake in common mycorrhizal networks: Role of intraradical fungal phosphate transporters

We have recently identified two genes coding for inorganic phosphate transporters (Pht) in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) that were induced in roots colonized by arbuscular mycorrhizal (AM) fungi. Mycorrhizal acquisition of inorganic phosphorus (Pi) was strongly affected by the combination of plant and AM fungal species, but the expression level of these genes coding for AM-inducible Pi transporters did not explain differences in plant phosphorus acquisition where flax and sorghum are sharing a common mycorrhizal network. In the present study, we investigated the possible role of fungal Pi transporters in the regulation of mycorrhizal Pi acquisition by measuring their expression in roots of flax and sorghum. One Pi transporter of Rhizophagus irregularis (RiPT5) showed a positive correlation with mycorrhizal Pi acquisition of sorghum. This indicates that a possible involvement in the regulation of mycorrhizal Pi acquisition. In general, expression of AMF Pi transporters was more related to mycorrhizal Pi acquisition of sorghum than of flax, indicating plant species-specific differences in the regulation of mycorrhizal Pi acquisition

Sinorhizobium meliloti -induced chitinase gene expression in Medicago truncatula ecotype R108-1: a comparison between symbiosis-specific classV and defence-related classIV chitinases

The Medicago truncatula (Gaertn.) ecotypes JemalongA17 and R108-1 differ in Sinorhizobium meliloti-induced chitinase gene expression. The pathogen-inducible classIV chitinase gene, Mtchit4, was strongly induced during nodule formation of the ecotype JemalongA17 with the S. meliloti wild-type strain 1021. In the ecotype R108-1, the S. meliloti wild types Sm1021 and Sm41 did not induce Mtchit4 expression. On the other hand, expression of the putative classV chitinase gene, Mtchit5, was found in roots of M. truncatula cv. R108-1 nodulated with either of the rhizobial strains. Mtchit5 expression was specific for interactions with rhizobia. It was not induced in response to fungal pathogen attack, and not induced in roots colonized with arbuscular mycorrhizal (AM) fungi. Elevated Mtchit5 gene expression was first detectable in roots forming nodule primordia. In contrast to Mtchit4, expression of Mtchit5 was stimulated by purified Nod factors. Conversely, Mtchit4 expression was strongly elevated in nodules formed with the K-antigen-deficient mutant PP699. Expression levels of Mtchit5 were similarly increased in nodules formed with PP699 and its parental wild-type strain Sm41. Phylogenetic analysis of the deduced amino acid sequences of Mtchit5 (calculated molecular weight = 41,810Da, isoelectric point pH7.7) and Mtchit4 (calculated molecular weight 30,527Da, isoelectric point pH4.9) revealed that the putative Mtchit5 chitinase forms a separate clade within classV chitinases of plants, whereas the Mtchit4 chitinase clusters with pathogen-induced classIV chitinases from other plants. These findings demonstrate that: (i) Rhizobium-induced chitinase gene expression in M. truncatula occurs in a plant ecotype-specific manner, (ii) Mtchit5 is a putative chitinase gene that is specifically induced by rhizobia, and (iii) rhizobia-specific and defence-related chitinase genes are differentially influenced by rhizobial Nod factors and Kantigen

Impact of antifungals producing rhizobacteria on the performance of Vigna radiata in the presence of arbuscular mycorrhizal fungi

Plant growth-promoting rhizobacteria (PGPR) that produce antifungal metabolites are potential threats for the arbuscular mycorrhizal (AM) fungi known for their beneficial symbiosis with plants that is crucially important for low-input sustainable agriculture. To address this issue, we used a compartmented container system where test plants, Vigna radiata, could only reach a separate nutrient-rich compartment indirectly via the hyphae of AM fungi associated with their roots. In this system, where plants depended on nutrient uptake via AM symbiosis, we explored the impact of various PGPR. Plants were inoculated with or without a consortium of four species of AM fungi (Glomus coronatum, Glomus etunicatum, Glomus constrictum, and Glomus intraradices), and one or more of the following PGPR strains: phenazine producing (P+) and phenazine-less mutant (P−), diacetylphloroglucinol (DAPG) producing (G+) and DAPG-less mutant (G−) strains of Pseudomonas fluorescens, and an unknown antifungal metabolite-producing Alcaligenes faecalis strain, SLHRE425 (D). PGPR exerted only a small if any effect on the performance of AM symbiosis. G+ enhanced AM root colonization and had positive effects on shoot growth and nitrogen content when added alone, but not in combination with P+. D negatively influenced AM root colonization, but did not affect nutrient acquisition. Principal component analysis of all treatments indicated correlation between root weight, shoot weight, and nutrient uptake by AM fungus. The results indicate that antifungal metabolites producing PGPR do not necessarily interfere with AM symbiosis and may even promote it thus carefully chosen combinations of such bioinoculants could lead to better plant growt

Erträge und Nährstoffgehalte von alten, biologisch und konventionell gezüchteten Winterweizensorten in verschiedenen landwirtschaftlichen Systemen

Due to limited nutrient conditions in organic farming winter wheat cultivars can often not perform to the full extent of their genetic potential. This study aims to assess nutrient acquisition potential and yields of old, organically and conventionally bred winter wheat cultivars. Ten cultivars were tested within the DOK long-term experiment in two organic systems at low and moderate intensity, a conventional stockless system and an unfertilized control. Yields and nutrient contents of grain and straw were significantly affected by cultivars and systems. Cultivar x system interactions were not detected. Yields were increasing with nutrient level and year of release of cultivars. Under organic conditions all cultivars performed equally well with respect to yield. Grain nitrogen content was increasing in line with nitrogen input, but dropping along year of release of cultivar

Arbuscular mycorrhizal fungal communities in sub-Saharan Savannas of Benin, West Africa, as affected by agricultural land use intensity and ecological zone

The rapid decline of soil fertility of cultivated lands in the sub-Saharan savannas of West Africa is considered to be the main cause of the increasingly severe constraints of food production. The soils in this tropical area are highly fragile, and crop yields are limited by characteristically low levels of available phosphorus. Under such preconditions, the multiple benefits of the arbuscular mycorrhizal (AM) symbiosis are likely to play a pivotal role for maintaining natural soil fertility by enhancing plant nutrient use efficiency, plant health, and stabilization of a favorable soil structure. Thus, it is important to explore the impact of the commonly applied farming practices on the native AM fungal community. In the present study, we determined the AM fungal species composition in three ecological zones differing by an increasingly prolonged dry season from South to North, from the Southern Guinea Savanna (SG), to the Northern Guinea Savanna (NG), to the Sudan Savanna (SU). In each zone, four "natural” and four "cultivated” sites were selected. "Natural” sites were three natural forest savannas (at least 25-30years old) and a long-term fallow (6-7years old). "Cultivated” sites comprised a field with yam (Dioscorea spp.) established during the first year after forest clearance, a field under mixed cropping with maize (Zea mays) and peanut (Arachis hypogaea), a field under peanut, and a field under cotton (Gossypium hirsutum) which was the most intensively managed crop. Soil samples were collected towards the end of the wet season in each zone. AM fungal spores were extracted and morphologically identified. Soil subsamples were used to inoculate AM fungal trap cultures using Stylosanthes guianensis and Brachiaria humidicola as host plants to monitor AM root colonization and spore formation over 10 and 24months, respectively. A total of 60 AM fungal species were detected, with only seven species sporulating in the trap cultures. Spore density and species richness were generally higher in the natural savannas and under yam than at the other cultivated sites and lowest under the intensively managed cotton. In the fallows, species richness was intermediate, indicating that the high richness of the natural savannas was not restored. Surprisingly, higher species richness was observed in the SU than in the SG and NG, mainly due to a high proportion of species in the Gigasporaceae, Acaulosporaceae, and Glomeraceae. We conclude that the West African savannas contain a high natural AM fungal species richness, but that this natural richness is significantly affected by the common agricultural land use practices and appears not to be quickly restored by fallo