87 research outputs found
Spread the news: systemic dissemination and local impact of Ca2+ signals along the phloem pathway
No full textFilamentous sieve element proteins are able to limit phloem mass flow, but not phytoplasma spread
Get PDFIn Fabaceae, dispersion of forisomes—highly ordered aggregates of sieve element proteins—in response to phytoplasma infection was proposed to limit phloem mass flow and, hence, prevent pathogen spread. In this study, the involvement of filamentous sieve element proteins in the containment of phytoplasmas was investigated in non-Fabaceae plants. Healthy and infected Arabidopsis plants lacking one or two genes related to sieve element filament formation—AtSEOR1 (At3g01680), AtSEOR2 (At3g01670), and AtPP2-A1 (At4g19840)—were analysed. TEM images revealed that phytoplasma infection induces phloem protein filament formation in both the wild-type and mutant lines. This result suggests that, in contrast to previous hypotheses, sieve element filaments can be produced independently of AtSEOR1 and AtSEOR2 genes. Filament presence was accompanied by a compensatory overexpression of sieve element protein genes in infected mutant lines in comparison with wild-type lines. No correlation was found between phloem mass flow limitation and phytoplasma titre, which suggests that sieve element proteins are involved in defence mechanisms other than mechanical limitation of the pathogen
Characterization of secondary metabolites and signaling pathways involved in microalgal-bacterial interactions
Get PDFA soil bacterium Pseudomonas protegens Pf-5 has antagonistic effects on the green microalga Chlamydomonas reinhardtii. P. protegens triggers cytosolic Ca2+ elevations in C. reinhardtii by using a mixture of secondary metabolites. Their IC50 values causing immobilization of the algal cells are in accordance with cytosolic Ca2+ elevations. The cyclic lipopeptide orfamide A causes the strongest immobilization with an IC50 value of only 4.1 µM, which can elevate the cytosolic Ca2+ and deflagellates the algal cells within 1 minute. We further investigated orfamide A triggered effects by using a series of chemically synthesized derivatives. The entire structure of orfamide A, the length of its N-terminal fatty acid tail as well as the stereochemistry of certain amino acids of orfamide A play key roles in its biological activities regarding Ca2+ signatures and deflagellation. Recently, we also performed an alanine scan, showing that most of the amino acids of orfamide A are relevant to maintain its biological activities. Interestingly, two Ca2+ signalling pathways are indicated by our studies. One is involved in the loss of cytosolic Ca2+ elevation and deflagellation. The other triggers a similar Ca2+ response than isolated orfamide A but causes significantly lower deflagellation rates. Using a modulator of Ca2+ channels and knock-out mutants, we found that at least four TRP-type Ca2+ channels (TRP5, TRP11, TRP15 and TRP22) are involved in orfamide A triggered deflagellation
A Poly(A) Ribonuclease Controls the Cellotriose-Based Interaction between <i>Piriformospora indica</i> and Its Host Arabidopsis
Get PDFHow phloem-feeding insects face the challenge of phloem-located defenses
Get PDFDue to the high content of nutrient, sieve tubes are a primary target for pests, e.g. most phytophagous hemipteran. To protect the integrity of the sieve tubes as well as their content, plants possess diverse chemical and physical defense mechanisms. The latter mechanisms are important because they can potentially interfere with the food-source accession of phloem-feeding insects. Physical defense mechanisms are based on callose as well as on proteins and often plug the sieve tube. Insects that feed from sieve tubes are potentially able to overwhelm these defense mechanisms using their saliva. Gel saliva forms a sheath in the apoplast around the stylet and is suggested to seal the stylet penetration site in the cell plasma membrane. In addition, watery saliva is secreted into penetrated cells including sieve elements; the presence of specific enzymes/effectors in this saliva is thought to interfere with plant defense responses. Here we detail several aspects of plant defense and discuss the interaction of plants and phloem-feeding insects. Recent agro-biotechnological phloem-located aphid control strategies are presented
Collection of phloem sap in phytoplasma-infected plants
No full textPhytoplasmas colonize specifically the phloem sieve elements (SEs) of plants and influence effectively the plant physiology. To study and understand the interaction of phytoplasmas and host plants an access to the cellular, microscale volume of SEs is demanded. Different methods are suitable to collect phloem sap of phytoplasma-infected plants. The two most common methods are the EDTA-facilitated exudation and the stylectomy. For the EDTA-facilitated method, the cut end of a leaf is placed into an EDTA solution. The EDTA prevents and avoids the Ca2+ dependent (re-) occlusion of SEs by binding Ca2+ ions and the mass flow of SEs is restarted which results in an outflow of the SE content into the EDTA bathing solution. The advantage is on the one hand a simple application and secondly, feasible for all plant species. The stylectomy method requires piercing-sucking insects like any aphids. During phloem-sap ingestion, the stylet is severed by a microcautery device or a laser from the insect body. Due to the high turgor pressure of the SEs the phloem sap is forced out through the remaining stylet and can be collected with a glass capillary, for example. The stylectomy delivers pure phloem sap, however, the collected volumes are in the range of nano liters and the temporal and staff costs are tremendous. A third method is the spontaneous exudation in phytoplasma-infected apple trees providing only in springtime large volumes of vascular sap after cutting along the bark. For the spontaneous exudation the proportion of phloem sap is unclear. Thus, this third method still needs a closer examination in prospective surveys
Isolation and Characterization of High-Efficiency Rhizobia From Western Kenya Nodulating With Common Bean
Get PDFCommon bean is one of the primary protein sources in third-world countries. They form nodules with nitrogen-fixing rhizobia, which have to be adapted to the local soils. Commercial rhizobial strains such as Rhizobium tropici CIAT899 are often used in agriculture. However, this strain failed to significantly increase the common bean yield in many places, including Kenya, due to the local soils’ low pH. We isolated two indigenous rhizobial strains from the nodules of common bean from two fields in Western Kenya that have never been exposed to commercial inocula. We then determined their ability to fix nitrogen in common beans, solubilize phosphorus, and produce indole acetic acid. In greenhouse experiments, common bean plants inoculated with two isolates, B3 and S2 in sterile vermiculite, performed better than those inoculated with CIAT899 or plants grown with nitrogen fertilizer alone. In contrast to CIAT899, both isolates grew in the media with pH 4.8. Furthermore, isolate B3 had higher phosphate solubilization ability and produced more indole acetic acid than the other two rhizobia. Genome analyses revealed that B3 and S2 are different strains of Rhizobium phaseoli. We recommend fieldwork studies in Kenyan soils to test the efficacy of the two isolates in the natural environment in an effort to produce inoculants specific for these soils
Measurement of Electropotential Waves in Intact Sieve Elements Using Aphids as Bioelectrodes
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