Molecular phylogeny of the mycorrhizal desert truffles (Terfezia and Tirmania), host specificity and edaphic tolerance

Terfezia and Tirmania, so called desert truffles, are mycorrhizal fungi mostly endemic to arid and semi-arid areas of the Mediterranean Region, where they are associated with Helianthemum species. The aim of this work was to study the phylogenetic relationships in these pezizalean hypogeous fungi. The restriction fragment length polymorphism (RFLP) and DNA sequences of internal transcribed spacers (ITS) of the nuclear rDNA were studied for several morphological species, Terfezia arenaria, T. boudieri, T. claveryi, T. leptoderma, T. terfezioides (=Mattirolomyces terfezioides), Tirmania nivea and T. pinoyi. The sequences were analyzed with distance and parsimony methods. Phylogenetic analyses indicated a close genetic relationship between Tirmania and Terfezia. They may have arisen from a single evolutionary lineage of pezizalean fungi that developed the hypogeous habit as an adaptation to heat and drought in Mediterranean ecosystems. This analysis also supports the re-establishment of the genus Mattirolomyces. The genera Tirmania and Terfezia were monophyletic, and morphological species corresponded to phylogenetic species. The Tirmania clade comprises desert truffles with smooth spores and amyloid asci, which were found in deserts. The Terfezia clade grouped species found in semi-arid habitats having ornamented and spherical spores. These species are adapted to exploit different types of soil (either acid or basic soils) in association with specific hosts (either basophilous or acidophilous species). Although other factors might also play a role, host specialization and edaphic tolerances (fungus and/or host tolerances) might be the key in the species diversity of these genera.     

Metal-binding capacity of arbuscular mycorrhizal mycelium

Experiments with excised mycelium of several Glomus spp. with different histories of exposure to heavy metals were carried out to measure their capacities to bind Cd and Zn. Cd sorption was followed for up to 6 h of incubation to determine its time course relationships. Controls treated with a metabolic inhibitor were included to evaluate whether sorption was due to active uptake or passive adsorption. The effect of ion competition (effects of Ca or Zn on Cd sorption) and general measurements of cation exchange capacity (CEC) of roots and hyphae were also performed. The results showed that AM mycelium has a high metal sorption capacity relative to other microorganisms, and a CEC comparable to other fungi. Metal sorption was rapid (<30 min) and appeared mainly to be due to passive adsorption. Adsorption was highest in a metal-tolerant G. mosseae isolate and intermediate for a fungus isolated from a soil treated with metal-contaminated sludge. The former adsorbed up to 0.5 mg Cd per mg dry biomass, which was three times the binding capacity of non-tolerant fungi, and more than 10 times higher than reported values for, e.g., the commonly used biosorption organism Rhizopus arrhizus. The implications of these results for AM involvement in plant protection against excess heavy metal uptake are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Extraradical mycelium network of arbuscular mycorrhizal fungi allows fast colonization of seedlings under in vitro conditions

Actively growing extraradical hyphae extending from mycorrhizal plants are an important source of inoculum in soils which has seldom been considered in vitro to inoculate young plantlets. Seedlings of Medicago truncatula were grown in vitro in the extraradical mycelium network extending from mycorrhizal plants. After 3, 6, 9, 12, and 15 days of contact with the mycelium, half of the seedlings were harvested and analyzed for root colonization. The other half was carefully transplanted in vitro on a suitable growth medium and mycelium growth and spore production were evaluated for 4 weeks. Seedlings were readily colonized after 3 days of contact with the mycelium. Starting from 6 days of contact, the newly colonized seedlings were able to reproduce the fungal life cycle, with the production of thousands of spores within 4 weeks. The fast mycorrhization process developed here opens the door to a broad range of in vitro studies for which either homogenous highly colonized seedlings or mass-produced in vitro inoculum is necessary. Liesbeth Voets and Ivan Enrique de la Providencia contributed equally to this work. MUCL is part of the Belgian Coordinated Collections of Micro-organisms (BCCM).     

Effect of drought stress on growth and water relations of the mycorrhizal association Helianthemum almeriense-Terfezia claveryi

 Plants of Helianthemum almeriense were micropropagated on MS medium and inoculated in vitro with Terfezia claveryi mycelium on MH medium and vermiculite. Mycorrhizal (M) and non-mycorrhizal (NM) plants were subjected to a drought stress period of 3 weeks in greenhouse conditions with the soil matric potential maintained at –0.5 MPa. Drought stress did not affect the amount of mycorrhizal colonization. The survival rate of M plants at the end of the drought stress period was higher than that of NM plants. The water potential was higher in M plants than in NM plants by 14% in well-watered and 26% in drought-stressed plants. Transpiration, stomatal conductance and net photosynthesis were higher in M plants than in NM plants. Transpiration was 92% higher in M plants than in NM plants under drought-stress conditions and 40% when irrigated. Stomatal conductance was 45% and 14% higher and net photosynthesis 88% and 54% higher, respectively, in M than in NM plants. Drought-stressed M plants accumulated more N, P and K than drought-stressed NM plants. Reduced negative effects of drought stress on H. almeriense by the desert truffle T. claveryi could be ascribed to specific physiological and nutritional mechanisms, suggesting that this mycorrhizal symbiosis aids adaptation to arid climates. Accepted: 7 July 2000     

Effects of water stress on cryptoendolithic cyanobacteria from hot desert rocks

Four strains of Chroococcidiopsis and one Chroococcus, all isolated from extreme arid desert rocks, and one marine Chroococcus, were subjected to water stress using both matric and osmotic control methods. For all Chroococcidiopsis strains, photosynthetic rates decreased with decreasing water potential. After 24h preincubation the decrease was linear but after 72h there was a sharp drop below-3400 kPa (a _w0.976). In contrast, the two Chroococcus strains showed optimum photosynthesis between-3000 and-4000 KPa. It appears, therefore, that Chroococcidiopsis in deserts may have a different survival strategy in response to aridity than Chroococcus (rare in deserts).Absolute rates of ¹⁴CO₂ uptake were higher in matric than in osmotic control systems. It is suggested that, in a matric experimental system, the water status is more representative of the natural conditions in arid environments.The consistent differences between different strains in their response to water stress suggest that this character in Cyanobacteria may be of taxonomic significance.     

Effect of water stress on the enzymes of nitrate metabolism in two Brassica species

Brassica juncea (drought susceptible) and B. campestris (drought tolerant) were germinated under simulated water stress created by polyethylene glycol (MW 6000). The two species showed characteristic differences in dry weight, nitrate reductase, aspartate amino transferase, alanine aminotransferase, glutamate dehydrogenase and free proline accumulation in the embryo axis under water stress. Stress resulted in the decreased activities of these enzymes and the decrease was more in B. juncea than in B. campestris. In both species, protein content was higher under stress. In B. juncea, a 12-fold increase in free proline occurred as compared to a 7-fold increase in B. campestris at ?6 atm osmotic potential.     

Comparative taxonomy of desert truffles of the Australian outback and the African Kalahari

An error in correcting page proofs of a previous paper led to an invalid new combination, Mattirolomyces westraliensis. Here the correct new combination, Mattirolomyces austroafricanus, is validated.     

Physiological parameters of desert truffle mycorrhizal Helianthemun almeriense plants cultivated in orchards under water deficit conditions

Physiological parameters of mycorrhizal symbiosis by Helianthemum almeriense and Terfezia claveryi in orchards were characterized under water deficit conditions. Our orchard included 40 mycorrhizal and 40 nonmycorrhizal plants. Only mycorrhizal plants survived at the beginning of the experimental period, indicating dependency on fungal symbionts in roots for survival. Drought stress significantly affected the mycorrhizal colonization percentage which was 70% in nonirrigated mycorrhizal and 48% in irrigated mycorrhizal plants. No significant differences in plant growth were observed between nonirrigated and irrigated mycorrhizal plants before and after drought stress. Stomatal conductance was more sensitive to water stress than shoot water potential. It decreased more than two-fold under drought-stress compared to control mycorrhizal plants under irrigation/light saturating conditions, indicating important stomatal closure with water deficit. Plants’ water use efficiency improved with drought with stomatal conductance values below 0.3 mol?m^?2?s^?1. The ability to maintain open stomata and photosynthesis under drought increased carbon supply for growth, and ascocarp fruiting which requires current photosynthates. Basically, H. almeriense shows a conservative water use strategy based mainly on avoiding drought stress by reducing stomatal conductance as soil water potential decreases and atmospheric conditions dry. The results show that mycorrhizal H. almeriense plants maintain good physiological parameters with low soil matric potentials, thus making them an alternative agricultural crop in arid/semi-arid areas.     

Effect of dietary preformed water on energy and water budgets of two sympatric desert rodents, Acomys russatus and Acomys calzivinus

Golden spiny mice ( Acomys russatus ) and common spiny mice ( Acomys cahirinus ) are omnivorous rodents that are sympatric in many rocky areas in Israeli deserts. They are similar in body size and diet habits. They differ in that A. cahirinus are nocturnal whereas A. russatus are diurnal and A. russatus inhabit extremely arid areas where A. cahirinus are absent. These differences led us to hypothesix that A. russatus are more conservative in their water needs and thererore are ahle to consumc a drier diet than A. chairinus. To test this hypothesis we oikrcd both species a dry ration and different numbers of snails and measured their energy and water intakes and their body mass changes.
Acomys russatus were capable of maintaining body mass on a much drier diet than A. cahirinus and therefore our hypothesis was supported. In order to maintain body mass A. cahirinus required about 2·1 ml/day (or about 4·7% body mass) preformed water, about twice the volume required by A. russatus. They also required a diet that had a water content of 48·3%, of the fresh matter, which was about 20% higher than that of A. russatus. The main reason why A. russatus needed less water was that they losl less by evaporation than A. cahirinus did. We suggest that the lower preformed water needs of A. russatus and their ability to consume a drier diet allom them to tolerate higher air temperatures and to inhabit extreme deserts where A. cahirinus are absent.     

Effect of water stress and heavy metals on induction of somatic embryogenesis in wheat leaf base cultures

In vitro cultures of plant tissues are known to mimic the response of field-grown plants when subjected to stress treatments. This investigation on Triticum aestivum explores the effect of drought stress on somatic embryogenesis and endogenous proline content. Leaf bases were cultured on MS medium supplemented with 2,4-D (10 microM) and different concentrations of PEG (2.5, 5, 7.5%) or mannitol (0.25 and 0.5 M) and also subjected to different periods of aerial drying in the laminar flow for one-day and subsequently transferred to MS basal medium. PEG treatment induced a high percentage (up to 50%) of embryoid formation. However, with mannitol and aerial drying, percentage of embryoid formation decreased with increasing concentrations and duration. After ten days, the endogenous proline content of explants treated with different concentrations of PEG, mannitol and different durations of aerial drying increased with increasing concentration and increasing duration of the treatment, thus, corroborating the role of proline as an osmolyte during stress conditions. Similarly, addition of metals such as cadmium and cobalt caused a reduction in percentage explants depicting embryogenesis. However, when cadmium was employed alone, 22% explants displayed somatic embryogenesis as compared to 54% in 2,4-D treated cultures.     

Effect of water stress on protein content in two maize cultivars differing in drought resistance

The changing pattern, of WSD and concomitant protein changes were scanned in twoZea mays cultivars, with differential sensitivity to water stress. Increasing protein values were recorded in resistant cv. Ageti-76 with decreasing osmotic potentials of substrate (on 3rd day of stress), although the values in susceptible cv. Vijay remained almost on a par with the controls. In another experiment both the cultivars revealed initial increase of protein on 2nd day at osmotic potentials of - 2 and -4 × 10⁶ Pa, however, values declined up to day 7 of stress. WSD showed an increasing trend in both the experiments, although slightly higher values of WSD were registered in cv. Ageti-76 in comparison with cv. Vijay. The significance of protein changes in reference to drought is discussed.     

Effect of triacontanol on plant cell cultures in vitro

Triacontanol [CH₃(CH₂)₂₈CH₂OH] increased growth in vitro of cell cultures of haploid tobacco (Nicotiana tabacum). The fresh weight of cell cultures of tomato (Lycopersicon esculentum), potato (Solanum tuberosum), bean (Phaseolus vulgaris), and barley (Hordeum vulgare x H. jubatum) was also increased. The increase in growth of tobacco callus seems to have been due to an increase in cell number. Another long chain alcohol, octocosanol [CH₃(CH₂)₂₆CH₂OH], did not increase the growth of tobacco cell cultures.     

Specific PCR-primers as a reliable tool for the detection of white truffles in mycorrhizal roots

During their symbiotic phase, white truffles are barely distinguishable morphologically, and molecular probes are needed for their identification. Here we report the design of species-specific primers for two white truffles ( Tuber magnatum and T. borchii ) on the basis of their ITS sequence. Their efficiency has been successfully tested on fruit bodies of the same species, many related and unrelated fungal species, as well as mycorrhizal roots in direct, nested and multiplex PCR experiments. They have allowed us to identify T. magnatum mycorrhizas for the first time.     

The effects of water deprivation and salt load on water conservation efficiency in two Indian desert gerbils

Summary The effects of water deprivation and intraperitoneal salt loading on urine volume and on various urinary constituents have been examined in two gerbil species of the Rajasthan desert, the Indian desert gerbil (Meriones hurrianae Jerdon) and the Indian gerbil (Tatera indica indica Hardwicke). During summer, hydratedT. indica excreted 0.782 ml urine·100 g^-1·d^-1 which was about 60.5% higher than the volume of urine excreted by hydratedM. hurrianae (0.487 ml·100 g^-1·d^-1). During winter, both species excreted around 1.5 ml urine ·100 g^-1·d^-1. The experimental treatments caused reductions in urine volume inM. hurrianae from 40 to 76% during summer and from 35 to 71% in winter. Similar treatments inT. indica caused reductions in urine volume of 50–82% in summer and 5–60% in winter. The mean increase in urine osmolarity following various salt loading treatments inT. indica ranged from 3800 to 5761 mosmol·l^-1 and from 4034 to 6255 mosmol·l^-1 during summer and winter, respectively. The mean values of urine osmolarity for hydratedT. indica were 2831 and 3189 mosmol·l^-1 during summer and winter, respectively. InM. hurrianae salt loading treatments caused increases of urine osmolarity between 3381 and 5646 mosmol·l^-1 and between 4032 and 5434 mosmol· l^-1, during summer and winter, respectively, over the values recorded for hydrated animals (summer=3292; winter=3294 mosmol·l^-1). A maximum urine osmolarity of around 7000 mosmol·l^-1 was found in both species when subjected to 2% salt-loading treatment. The treatments used in this study increased urinary urea level in bothT. indica (3039–4056 mM) and inM. hurrianae (1900–2180 mM) compared to the level in their respective hydrated controls (T. indica=1628 mM;M. hurrianae=1372 mM). The results indicate thatT. indica may be better adapted to produce more concentrated urine thanM. hurrianae.     

Effect of steam sterilization of soil on two desert plant species

Summary Franseria dumosa Gray and Hilaria rigida (Thurb.) Benth. ex Scribn. seedlings were grown in a glasshouse in potted soil which was collected from the Mojave Desert near Mercury, Nevada. The soil represented areas under living shrubs and also areas between shrubs. Soil was either steam sterilized or not steam sterilized. The sterilization resulted in greatly decreased yields of plants possibly because of induced P deficiency. It was suggested that symbiotic mycorrhizae necessary for P absorption for the species involved might have been eliminated by the sterilization. The effect did not hold for a noncalcareous soil well supplied with available P. Soil sterilization increased both Mn and Zn in plants. There was an interaction in that plants did not grow well in soil from under shrubs regardless of steaming indicating possible allelopathic effects. re]19720711