Population Response of Rhizosphere Microbiota of Garden Pea Genotypes to Inoculation with Arbuscular Mycorrhizal Fungi.

This study of a legume's rhizosphere in tripartite symbiosis focused on the relationships between the symbionts and less on the overall rhizosphere microbiome. We used an experimental model with different garden pea genotypes inoculated with AM fungi (Rhizophagus irregularis and with a mix of AM species) to study their influence on the population levels of main trophic groups of soil microorganisms as well as their structure and functional relationships in the rhizosphere microbial community. The experiments were carried out at two phenological cycles of the plants. Analyzes were performed according to classical methods: microbial population density defined as CUF/g a.d.s. and root colonization rate with AMF (%). We found a proven dominant effect of AMF on the densities of micromycetes and actinomycetes in the direction of reduction, suggesting antagonism, and on ammonifying, phosphate-solubilizing and free-living diazotrophic Azotobacter bacteria in the direction of stimulation, an indicator of mutualistic relationships. We determined that the genotype was decisive for the formation of populations of bacteria immobilizing mineral NH4+-N and bacteria Rhizobium. We reported significant two-way relationships between trophic groups related associated with soil nitrogen and phosphorus ions availability. The preserved proportions between trophic groups in the microbial communities were indicative of structural and functional stability.

Hormonomic Changes Driving the Negative Impact of Broomrape on Plant Host Interactions with Arbuscular Mycorrhizal Fungi.

Belowground interactions of plants with other organisms in the rhizosphere rely on extensive small-molecule communication. Chemical signals released from host plant roots ensure the development of beneficial arbuscular mycorrhizal (AM) fungi which in turn modulate host plant growth and stress tolerance. However, parasitic plants have adopted the capacity to sense the same signaling molecules and to trigger their own seed germination in the immediate vicinity of host roots. The contribution of AM fungi and parasitic plants to the regulation of phytohormone levels in host plant roots and root exudates remains largely obscure. Here, we studied the hormonome in the model system comprising tobacco as a host plant, Phelipanche spp. as a holoparasitic plant, and the AM fungus Rhizophagus irregularis. Co-cultivation of tobacco with broomrape and AM fungi alone or in combination led to characteristic changes in the levels of endogenous and exuded abscisic acid, indole-3-acetic acid, cytokinins, salicylic acid, and orobanchol-type strigolactones. The hormonal content in exudates of broomrape-infested mycorrhizal roots resembled that in exudates of infested non-mycorrhizal roots and differed from that observed in exudates of non-infested mycorrhizal roots. Moreover, we observed a significant reduction in AM colonization of infested tobacco plants, pointing to a dominant role of the holoparasite within the tripartite system.

GC-MS Composition and Olfactory Profile of Concretes from the Flowers of Four Nicotiana Species.

The genus Nicotiana (Solanaceae) includes over 70 species, with a long history of traditional use; many of them are nowadays used in bioengineering, biosynthesis, molecular biology, and other studies, while common tobacco, N. tabacum L., is one of the most economically important industrial crops worldwide. Although Nicotiana species have been extensively investigated, relatively less research has focused on flowers, especially research related to obtaining aromatic products for cosmetic and perfumery use. On the other hand, there is evidence that Nicotiana flowers accumulate various secondary metabolites with a distinct aroma and biological activities, and the flowers represent a biomass available in sufficient quantities. Therefore, this study aimed to determinate the chemical composition (by GC-MS) and the olfactory profiles of a specific type of natural aromatic product (concrete), obtained from the flowers of four Nicotiana species, in a direct comparison between them. The yields of extracted concrete were sufficiently high, varying between the species, 1.4% (N. rustica L.), 2.5% (N. glutinosa L.), 1.6% (N. alata Link&Otto genotype with white flowers), 2.7% (N. alata genotype with pink flowers), 3.2% (N. tabacum, Oriental type), and 5.2% (N. tabacum, Virginia type). The major components of the obtained concretes belonged to different chemical classes: N. rustica and N. tabacum (OR), the hydrocarbons n-tetratriacontane (14.5%; 15.0%) and n-triacontane (12.1%; 13.3%), and 3-methyl-pentanoic acid (11.1%; 12.2%); N. glutinosa, the diterpenes sclareol (25.9%), 3-α-hydroxy-manool (16.3%), and 13-epimanool (14.9%); N. alata (WF), the phenylpropanoid terephthalic acid and di(2-ethylhexyl) ester (42.9%); N. alata (PF), the diterpene tributyl acetylcitrate (30.7%); and N. tabacum (FCV), the hydrocarbons n-hexacosane (12.9%) and n-pentacosane (12.9%). Each of the flower concretes revealed a characteristic odor profile. This is the first report about Nicotiana species as a source for obtaining flower concretes; these initial results about the concrete yield, olfactory profile, and chemical composition are a prerequisite for the possible processing of Nicotiana flowers into new aromatic products for use in perfumery and cosmetics. The study provides new data in favor of the potential of the four Nicotiana species as aromatic plants, as well as a possible alternative use of flowers, a valuable, but discarded, plant material in other applications.

Terpenoids in the Essential Oil and Concentrated Aromatic Products Obtained from Nicotiana glutinosa L. Leaves.

N. glutinosa L. is a relatively less studied Nicotiana species (Solanaceae), although there are data about its importance as a model plant in viral control studies, as a gene donor in tobacco hybridization and as a source of agents with insecticidal or fungicidal effects. The biological activities of the species were associated mostly with the presence of leaf surface metabolites, in particular diterpenes and sucrose esters. The aim of this study was to identify the chemical composition of the essential oil (EO) and two aromatic extraction products (concrete and resinoid) obtained from N. glutinosa L. leaves. GC-MS analysis identified 26 components in the EO (representing 97.3% of total oil content), which contained mostly diterpene compounds with major components manool (14.2%), sclarene (8.4%) and manoyl oxide (8.1%). The number of compounds identified in the concrete was 37 (95.5% of the total content) and the major component was the diterpene alcohol sclareol (14.2%). In the resinoid, 30 volatile components (representing 95.1% of resinoid content) were identified, with major components nicotine (32.9%), α-tocopherol (8.2%), tridecanoin (6.9%), sclareol (6.9%), and solanone (6.9%). The group of bicyclic diterpenes had the largest share in the diterpene fraction of the products (57.3%, 91.7%, and 86.3%, respectively for the EO, concrete, and resinoid). Considering the abundance of sclareol in the aromatic products, the antimicrobial activity of the pure substance was determined. Sclareol was highly effective against a set of medicinally important yeasts; Candida albicans АТСС 10231, C. glabrata ATCC 90030, C. parapsilosis clinical isolate, and C. tropicalis NBIMCC 23, while being less effective against the studied Gram-positive and Gram-negative bacteria. Data from the study on N. glutinosa aromatic products composition may be of interest to the aroma industries for their possible use in perfumery and cosmetics.