Christiane Charest

INFLUENCE OF ARBUSCULAR MYCORRHIZAE ON THE METABOLISM OF MAIZE UNDER DROUGHT STRESS

A greenhouse experiment was carried out to investigate the influence of the arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on metabolic changes in tropical maize (Zea mays L.) under drought. Two cultivars, Tuxpeno sequia CO (drought sensitive) and C8 (drought resistant), were subjected for 3 weeks to water stress following tasselling (75–95 days after sowing). Fully expanded 7th or 8th leaves were sampled and assessed for levels of chlorophyll, sugars, proteins, and amino acids. Chlorophyll content was not altered either by water stress or the presence of mycorrhizae. Mycorrhizal plants (M+) had higher total and reducing sugars than nonmycorrhizal plants (M-) at the end of 3 weeks of the drought cycle. An increase in protein content was observed with drought stress in M + plants of the cultivar C0. Most of the amino acids showed a linear increase during the period of water stress in M+ and M- plants for both cultivars. Total amino acids increased by 40.6% and 43.7% in M- plants of C0 and C8, respectively. With the presence of AM fungus, amino acid levels increased by only 10.7% and 19.2% of leaf dry mass in C0 and C8, respectively. Alanine, asparagine, glutamine, and glycine accounted for 70% of the amino acid pool. Under drought, AM inoculation enabled the plants to retain considerable amounts of sugars and proteins, especially in the drought-sensitive cultivar C0. This may be of physiological importance in helping the plant to withstand moderate drought.

The effect of vesicular-arbuscular mycorrhizae and chilling on two hybrids of Zea mays L.

In order to investigate the effect of vesicular-arbuscular mycorrhizae on the chilling resistance of Zea mays, seeds of two hybrids (Pioneer 3902 and Pride 5) were grown in soil inoculated with Glomus mosseae. Germination tests at 10° C and 25° C showed that Pride 5 was more resistant to chilling than Pioneer 3902. Plants grown at 25° C for 6 weeks were given a 1-week chilling treatment at 10° C and the responses of mycorrhizal and nonmycorrhizal plants of the two hybrids were compared. At 10° C, the mycorrhizal plants had greater biomass, carbohydrate, and protein content than the nonmycorrhizal plants.

Effect of arbuscular mycorrhizal colonization of four species of glomus on physiological responses of maize

Abstract This greenhouse study aimed to analyze the impact of arbuscular mycorrhizal (AM) fungal associations on maize (Zea mays L. hybrid Pioneer 3905) in order to compare their functional compatibility and efficiency. The AM fungus species used for this study were Glomus aggregatum, G. etunicatum, G. mosseae, and G. versiforme. Shoot and leaf masses, chlorophyll, soluble protein, total and reducing sugar, carbon (C), and nitrogen (N) concentrations, and glutamine synthetase (GS) activity in the maize leaves were analyzed. The root colonization ranged from 26% to 72% depending on the AM fungus species. Leaf mass was significantly higher when maize plants were colonized with G. etunicatum in comparison to the non‐AM control. The mycorrhizal effect on dry leaf mass ranged from 15.9% to 23.9% depending on the AM species. However, the total shoot mass did not differ significantly among the treatments. The mycorrhizal treatment had a marginally significant effect on the chlorophyll concentrations in maize lea...

Some like it toxic

Humans are notorious for disturbing terrestrial ecosystems worldwide, especially those that are in close proximity to urban areas. This disturbance has involved the accumulation of various types of chemical pollutants, of either agricultural or industrial origins, in both soil and water ecosystems. Pollutants have sometimes included essential plant nutrients, such as phosphate and nitrate, which have piled up throughout the years in many ecosystems as a consequence of aggressive agricultural practices, and a number of toxic or trace metals, e.g. iron, nickel or zinc that are important at low levels for the fitness of living organisms, but otherwise toxic at high concentrations ( Ker & Charest 2010 ; Audet & Charest 2008 ). In order to reduce the load of toxic elements, scientists have used the natural capacity of several plant species to sequestrate them from the soil and, ultimately, render them harmless. This process, called phytoremediation, is rather slow, as most plants take years to build up their biomass but has been shown to be ‘boostable’ under experimental conditions in the presence of a particular group of plant symbionts in the soil – the arbuscular mycorrhizal fungi (AMF) ( Gohre & Paszkowski 2006 ). These latter organisms are now widely recognized as being very beneficial for purposes of phytoremediation, but their biodiversity in the most disturbed ecosystems is still virtually unknown. Are these fungi really abundant in heavily polluted soils, or are their communities shrunken down like those of other microorganisms in the presence of heavy pollution? In this issue of Molecular Ecology, the study by Hassan et al. (2011) provides answers to these specific questions by determining the extent of AMF biodiversity across several urbanized areas in the City of Montréal.

Identification of constraining experimental-design factors in mycorrhizal pot-growth studies

In the objective of testing the design of pot-growth experiments, we conducted two greenhouse studies of a “dwarf” sunflower cultivar and an arbuscular mycorrhizal (AM) fungus to determine how pot size and inoculum distribution affect plant growth and AM symbiosis. As predicted, large-potted plants developed a greater overall biomass and root colonization than small-potted ones which we attributed to the larger “rootable” volume. Furthermore, plants grown in a band of high density inoculum substrate showed a higher prevalence of fungal vesicles (sites of lipid storage) indicating a more advanced level of root colonization compared to those grown in a dispersed inoculum substrate; this likely being due to the higher frequency of interaction between roots and fungal propagules. In a second experiment, large-potted AM plants showed a greater tolerance to water deficit than non-AM control plants; however, this mycorrhizal effect was not detected among small-potted plants. We conclude that careful consideration should be made toward design parameters to limit result biases and ultimately facilitate comparison of findings between studies.

Determining the Impact of the AM-Mycorrhizosphere on “Dwarf” Sunflower Zn Uptake and Soil-Zn Bioavailability

An in vivo compartmental pot greenhouse experiment involving “dwarf” sunflower and an arbuscular mycorrhizal (AM) fungus was designed to assess the contribution of non-AM roots (rhizosphere), AM roots and extraradical hyphae (mycorrhizosphere), or strictly extraradical hyphae (hyphosphere) on plant growth, plant metal uptake, and soil parameters using the micronutrient zinc (Zn) as a typical metal contaminant. We observed that, at high soil-Zn concentrations, the mycorrhizosphere treatments had lower Zn concentrations (especially in shoots and flowers) and a lower incidence of leaf chlorosis than the rhizosphere treatments. These phytoprotective effects are believed to be related to AM-induced biosorption processes that reduce soil metal bioavailability to delay the onset of plant metal toxicity. We also observed that the presence of extraradical hyphae causes a slight alkalinisation of the proximal soil environment whereas roots tended to acidify it, this having significant consequences toward metal bioavailability. Altogether, the AM symbiosis is considered to be a key component of ecosystem function involved in buffering plant growth conditions due to the processes of metal biosorption and hyphal alkalinisation which could contribute in enhancing the soils resiliency.

Assessing arbuscular mycorrhizal plant metal uptake and soil metal bioavailability among ‘dwarf’ sunflowers in a stratified compartmental growth environment

Using the micronutrient zinc (Zn) as a metal contaminant, a stratified compartmental pot greenhouse experiment involving ‘dwarf’ sunflowers and an arbuscular mycorrhizal (AM) fungus was designed to assess the role of AM symbiosis toward plant growth and metal uptake, and to differentiate its impact toward edaphic parameters across different soil strata. Consistent with previous hypotheses, AM plants contained up to 40% lower metal concentrations in their shoots than non-AM plants, particularly at the highest soil Zn levels (200 and 400 mg Zn kg−1 dry soil); this, corresponding with an enhanced growth status among AM plants. Upon assessing the soil Zn concentrations and pH, AM treatments also tended to have higher soil Zn levels and more alkaline conditions compared to non-AM treatments. This was found especially in the topmost soil stratum where AM root colonization was deemed most active as evidenced by a higher frequency of extraradical hyphae, vesicles, and arbuscules. Together, these effects were putatively linked to the AM-induced mechanism of metal biosorption known to modulate soil nutrient bioavailability and even delay the onset of metal toxicity.

In situ Turfgrass Establishment: I. Responses to Arbuscular Mycorrhizae and Fertilization

ABSTRACT A two-year field study was conducted to evaluate the impact of fertilization and arbuscular mycorrhizae on the in situ establishment of turfgrasses in low and high phosphorus content experimental sites. Organic or chemical fertilizers were applied on Kentucky Blue-grass and Creeping Bentgrass plots inoculated with either Glomus mosseae, G. aggregatum or G. intraradices. The arbuscular mycorrhizal control was made from original soils with their respective indigenous fungal populations. Soil surveys for indigenous Glomales populations revealed the predominance of Gigaspora margarita and Scutellospora calospora species at the high and low P sites, respectively. Both turfgrass species showed higher root colonization levels, up to 60%, at the low phosphorus soil site. Root colonization levels of Creeping Bentgrass were found to be almost twice those of Kentucky Bluegrass for all mycorrhizal treatments. The average growth rates of aerial parts were not affected by either mycorrhizal or fertilization treatments. Statistical analyses showed a significant interaction (P ≤ 0.05) between high and low phosphorus sites for Creeping Bentgrass, and root colonization levels, especially with G. intraradices treatment. For both turfgrass species, fertilization and site effects were predominant. As turfgrass is highly dependent on soil quality and as arbuscular mycorrhizal benefits vary with plant species, special care in the development of turfgrass management practices should be taken into account to optimize the arbuscular mycorrhizal turfgrass establishment process.

Influence of arbuscular mycorrhizal fungi and a root endophyte on the biomass and root morphology of selected strawberry cultivars under salt conditions

Sinclair, G., Charest, C., Dalpé, Y. and Khanizadeh, S. 2013. Influence of arbuscular mycorrhizal fungi and a root endophyte on the biomass and root morphology of selected strawberry cultivars under salt conditions. Can. J. Plant Sci. 93: 997-999. The influence of four arbuscular mycorrhizal fungi (AMF) (Glomus arenarium, G. caledonium, G. irregulare, and G. mosseae) and a root endophyte species (Piriformospora indica - Sebacinales) was investigated on four “day-neutral” strawberry (Fragaria×ananassa Duch.) cultivars (Albion, Charlotte, Mara des Bois, and Seascape) for their tolerance to salt stress. Fungal symbiosis tended to benefit strawberry plants in their tolerance to salinity, confirming the potential use of mycorrhizal biotechnology in horticulture in arid areas.

EFFECT OF NITROGEN STRESS ON GROWTH, SOLUBLE METABOLITES, AND GLUTAMINE SYNTHETASE ACTIVITY OF JACK PINE CALLUS CULTURES

Jack pine (Pinus banksiana Lamb.) callus cultures were grown in half-strength unmodified Litvay medium (control) and in media containing either no-nitrogen or nitrate. Almost no growth occurred in absence of nitrogen and in medium containing only nitrate. Glutamine synthetase (GS) activity was drastically reduced in comparison to callus grown in control medium. The pool of amino acids decreased by 66% in medium containing nitrate, and further by 50% in absence of nitrogen. Meanwhile total and reducing sugars sharply increased, and were 14 times higher in N-NO3 − and 22 times higher in nitrogen-free medium. Thirteen amino acids were identified in the control. Changes in the abundance and the relative content of amino acids confirmed that glutamine is the preferred nitrogen transport compound in Pinus. Jack pine cultures seemed to have a low capacity for nitrate uptake and assimilation as shown by the low GS activity and the decrease of glutamine content in nitrate-fed calli.