Pathways of Phosphorus Absorption and Early Signaling between the Mycorrhizal Fungi and Plants

This review highlights the key role that mycorrhizal fungi play in making phosphorus (Pi) more available to plants, including pathways of phosphorus absorption, phosphate transporters and plant-mycorrhizal fungus symbiosis, especially in conditions where the level of inorganic phosphorus (Pi) in the soil is low. Mycorrhizal fungi colonization involves a series of signaling where the plant root exudates strigolactones, while the mycorrhizal fungi release a mixture of chito-oligosaccharides and liposaccharides, that activate the symbiosis process through gene signaling pathways, and contact between the hyphae and the root. Once the symbiosis is established, the extraradical mycelium acts as an extension of the roots and increases the absorption of nutrients, particularly phosphorus by the phosphate transporters. Pi then moves along the hyphae to the plant root/fungus interface. The transfer of Pi occurs in the apoplectic space; in the case of arbuscular mycorrhizal fungi, Pi is discharged from the arbuscular to the plant’s root symplasm, in the membrane that surrounds the arbuscule. Pi is then absorbed through the plant periarbuscular membrane by plant phosphate transporters. Furthermore, plants can acquire Pi from soil as a direct absorption pathway. As a result of this review, several genes that codify for high-affinity Pi transporters were identified. In plants, the main family is Pht1 although it is possible to find others such as Pht2, Pht3, Pho1 and Pho2. As in plants, mycorrhizal fungi have genes belonging to the Pht1 subfamily. In arbuscular mycorrhizal fungi we found L1PT1, GiPT, MtPT1, MtPT2, MtPT4, HvPT8, ZmPht1, TaPTH1.2, GmosPT and LYCes. HcPT1, HcPT2 and BePT have been characterized in ectomycorrhizal fungi. Each gene has a different way of expressing itself. In this review, we present diagrams of the symbiotic relationship between mycorrhizal fungi and the plant. This knowledge allows us to design solutions to regional problems such as food production in soils with low levels of Pi.

     

Insights on the Behavior of Late Paleozoic Aquatic Crustaceans (Pygocephalomorpha?): Compound Trace Fossils from Western Argentina

We describe intergradations between the arthropod repichnial trace fossils Diplichnites gouldi (Gevers et al., 1971), Dendroidichnites Demathieu et al., 1992, and Monomorphichnus Crimes, 1970 with two distinct cubichnial traces, Gluckstadtella cooperi Savage, 1971 and Huilmuichnus santracruzensis new ichnogenus and ichnospecies. These compound ichnofossils are part of high ichnodiversity arthropod-dominated trace fossil associations from the Late Carboniferous Agua Escondida Formation of the San Rafael Basin (Argentina). The complex ichnotaxonomy of Diplichnites and the ichnospecies D. gouldi are discussed and some possible working solutions are proposed. The most likely producer of the compound trace fossils are the Pygocephalomorpha, a group of Late Paleozoic crustaceans that are recorded in nearby basins from Uruguay and Brazil. The compound trace fossils are used to infer a number of complex behaviors of pygocephalomorphs in a subaqueous setting, including caridoid (tail flip) or more primitive escape reactions, landing followed by resting and transient resting during normal walking. In addition, different gaits can be inferred from well-preserved D. gouldi, which can be correlated with contrasting trackway morphology.     

Apoptotic rate: a new indicator for the quantification of the incidence of apoptosis in cell cultures

BACKGROUND: Late apoptotic cells divide into apoptotic bodies and are missed by current detection methods. This results in an artificially low apoptotic index (AI). METHODS: This study proposes a flow cytometry-based ratiometric method that uses an internal reference standard of microbeads combined with fluorescein-annexin V binding and 7-aminoactinomycin D to enumerate viable, necrotic, and early and late apoptotic cells within specific subsets of a heterogeneous culture. RESULTS: In the absence of cell growth, the number of apoptotic cells that undergo fragmentation into apoptotic bodies in culture can also be determined accurately by this method. This information can then be used to obtain the apoptotic rate (AR), a new indicator of apoptosis that calculates the proportion of cells that have undergone apoptosis with respect to the total number of seeded cells. The main limitation of the method is that the AR is only suitable for the study of apoptosis in noncycling cells. CONCLUSIONS: This study reveals the superiority of the proposed method over the widely used Nicoletti method and current annexin-V binding methods. The AI did not reflect the true incidence of lymphocyte apoptosis, neither in response to lectins or phorbol esters, nor to serum deprivation. AR was more sensitive than AI, detecting apoptosis at lower concentrations of cell death inducers in all the subsets studied.     

Can submerged macrophytes be effective for controlling waterborne phytopathogens in irrigation ponds? An experimental approach using microcosms

Irrigation ponds may act as a source of phytopathogenic species that might infest crops through the irrigation systems. Many studies have shown that submerged macrophytes can improve water clarity by out-competing phytoplankton by means of various mechanisms: favoured phytoplankton-grazing zooplankton, reduced nutrient and light availability, increased sinking losses and the release of allelopathically active substances. However, less information is available on the effects of submerged macrophytes on heterotrophic aquatic organisms such as pathogenic bacteria, fungi or oomycete species. This paper studies the effects of three submerged macrophytes—Chara fragilis, Potamogeton pectinatus and Najas marina—on the viability in water of propagules of two phytopathogenic isolates of the oomycetes Pythium aphanidermatum and Pythium ultimum. Moreover, we tested general antimicrobial properties (against bacteria and fungi in water) for these macrophytes. The results showed clear inhibitory effects of all three macrophytes on bacterial density in water and of C. fragilis on the viability of Pythium. Thus, preserving aquatic vegetation in irrigation ponds (i.e. charophytes), besides its purely environmental interest, may have important agronomic benefits owing to their role as biological control against some phytopathogenic agents.     

Characterization of kinetic parameters and the formation of volatile compounds during the tequila fermentation by wild yeasts isolated from agave juice

The production of aroma compounds during tequila fermentation using four native yeast strains isolated from agave juice was quantified at controlled (35 degrees C) and uncontrolled temperatures (room temperature) by gas chromatography (FID). Three of the four strains were identified as Saccharomyces cerevisiae (MTLI 1, MALI 1 and MGLI 1) and one as Kloeckera apiculata (MALI 2). Among the aroma compounds produced, acetaldehyde has the highest accumulation at the controlled temperature and before 50% of sugar was consumed. The S. cerevisiae strains produced ethyl acetate in almost the same quantity at a concentration of 5 mg/L and the K. apiculata produced six-times more (30 mg/L) than the S. cerevisiae strains, independent of the fermentation temperature. The rate and amount of 1-propanol, amyl alcohols and isobutanol production were affected by the type of yeast used. The K. apiculate strain produced 50% less of the higher alcohols than the Saccharomyces strains. The results obtained showed that indigenous isolated yeasts play an important role in the tequila flavor and suggest that mixtures of these yeasts may be used to produce tequila with a unique and desirable aroma.     

A chemotaxonomic study of nine Canarian Sideritis species

Nine taxa of the Sideritis genus, Sideritis argosphacelus var. spicata, Sideritis candicans var. eriocephala,Sideritis discolor, Sideritis kuegleriana, Sideritis lotsyi, Sideritis lotsyi var. mascaensis, Sideritis marmorea, Sideritis soluta and Sideritis tenoi, which are endemic from the Canary Islands, have been chemically studied. The diterpene sicanatriol 7β,18-diacetate was obtained from S.argosphacelus var. spicata, whilst a nor-diterpene, epiadejone, and the 3(2H)-benzofuranone solutin have been found in S. soluta. Another diterpene, sidendrodiol 18-monoacetate, has been isolated from S.argosphacelus var. spicata, for the first time as a natural product. Known sesquiterpenes, diterpenes, triterpenes, sterols, flavones, coumarins and other aromatic derivatives have also been isolated. These studies support the botanical division of the genus into two subgenera, Sideritis and Marrubiastrum, the three sections of the latter subgenus, Cretica, Empedocleopsis and Marrubiastrum, and the elevation of S. argosphacelus var. spicata, S. candicans var. eriocephala and S. lotsyi var. mascaensis to the rank of species.     

Disturbance from pond management obscures local and regional drivers of assemblages of primary producers

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Gypsophile Chemistry Unveiled: Fourier Transform Infrared (FTIR) Spectroscopy Provides New Insight into Plant Adaptations to Gypsum Soils

Gypsum soils are among the most restrictive and widespread substrates for plant life. Plants living on gypsum are classified as gypsophiles (exclusive to gypsum) and gypsovags (non-exclusive to gypsum). The former have been separated into wide and narrow gypsophiles, each with a putative different ecological strategy. Mechanisms displayed by gypsum plants to compete and survive on gypsum are still not fully understood. The aim of this study was to compare the main chemical groups in the leaves of plants with different specificity to gypsum soils and to explore the ability of Fourier transform infrared (FTIR) spectra analyzed with neural network (NN) modelling to discriminate groups of gypsum plants. Leaf samples of 14 species with different specificity to gypsum soils were analysed with FTIR spectroscopy coupled to neural network (NN) modelling. Spectral data were further related to the N, C, S, P, K, Na, Ca, Mg and ash concentrations of samples. The FTIR spectra of the three groups analyzed showed distinct features that enabled their discrimination through NN models. Wide gypsophiles stood out for the strong presence of inorganic compounds in their leaves, particularly gypsum and, in some species, also calcium oxalate crystals. The spectra of gypsovags had less inorganic chemical species, while those of narrow gypsum endemisms had low inorganics but shared with wide gypsophiles the presence of oxalate. Gypsum and calcium oxalate crystals seem to be widespread amongst gypsum specialist plants, possibly as a way to tolerate excess Ca and sulphate. However, other mechanisms such as the accumulation of sulphates in organic molecules are also compatible with plant specialization to gypsum. While gypsovags seem to be stress tolerant plants that tightly regulate the uptake of S and Ca, the ability of narrow gypsum endemisms to accumulate excess Ca as oxalate may indicate their incipient specialization to gypsum.