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Flashcards by ruby.white94, updated more than 1 year ago
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Created by ruby.white94
over 10 years ago
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| Question | Answer |
| What species prodominates in rhizosphere? | Psuedomonas |
| Where is nutrient release greatest on roots? | Where lateral roots branch off |
| What are areas where lateral roots branch off? | Favoured sites for colonisation and infection |
| What do the products that are diffused from the rhizosphere do? | They influences the microflora |
| What is rhizosphere research aiming to do? | Replace agrichemicals by using beneficial microbes to influence plant growth and pathogen susceptibility |
| Erwinia carotarova | Soft rot pathogen of potatoes |
| What are pathogens to food supply? | Major and chronic threat to world food supply can come resistant to pesticides etc |
| PGPR | Plant growth promoting rhizophere |
| Direct effects of beneficial microbes | facilitate nutrient uptake e.g. nitrogen fixation and sulphur oxidation Synthesise compounds that affect plant growth ACC deaminase which inactivates precursor of stress hormone ethylene |
| What does ACC deaminase do? | Protects plants from salt stress |
| Indirect affects of beneficials | Lessen or prevent affect of pathogen |
| Pseudomonas fluorescens and root rot | P.fluorescens can control root rot by competition |
| Take-all | Fungal disease of wheat caused by Ggt |
| Take-all decline | In cases where wheat is monocultured natural suppression of Ggt occurs over time. corrulates with development of pseudomonas population. |
| Why does pythium ultimum kill Ggt? | produces antibiotics that kill the fungus production of 2-4-diacetylphloro-glucinol specifically implicated |
| Antibiosis | Bacteria colonises root and delivers antibiotic to the root thereby killing other infecting organisms |
| Induced systematic resistance | Local root colonisation sufficient to induce ISR. |
| Competition for niches and nutrients | Biocontrol bacteria acting through this mechanism outcompete fast the other organisms |
| Niche exclusion | Competetion for attachment and infection sites |
| Substrate competition | Competition for nutrients mashing of signal compunds |
| Antibiotics | Play a major role |
| Phylloplane | Leaf surface |
| What is the environment like on the phylloplane? | Harsh, rapid moisture influxs, rapis temp fluctuations and UV radiation |
| What type of bacteria inhabit the phylloplane? | Epiphytic gram negative |
| Pseudomonas syringae pr actinidiae | Plant pathogen of phylloplane |
| Secretion of Auxin | Causes plant to release sacchrides from the plant cell wall P.syringae |
| Syringomycin | Acts as a phototoxin and a surfactant Affects release of nutrients |
| EPS in P.syringae | Helps protect from environmental stresses |
| What does Ice nucleation active mean? | The bacteria functions are a nuclei for the formation of ice crystals that then spread into plant tissue P.syringae |
| What does ice nucleation prevent? | Supercooling of leaves Frost damage occurs at -2 instead of -8 |
| What is ice nucleation dependant on? | INA out-membrane protein |
| Ina- mutants | Used as competition for INA bacteria results inconclusive |
| Rain making bacteria | Bacteria swept into atomsphere by wind off plants, ice crystals form around them, turns to rain. Lands on leaf cycle continues |
| Fire blight and pre-emptive competition | Can prevent fire blight causing bacterium E.amylovora from infecting by the flower surface already being colonised by P.fluorescens |
| Advantages of microbial biocontrol? | Specific, target site of action, low toxicity, longevity |
| Disadvantages of microbial biocontrol | Inconsistent performance, flood drought, change in pH, changes in root exudate Slow rate of control specificity Self life |
| What type of bacteria is Rhizobium? | Gram -ve rod |
| What is the rhizobium legume symbiosis like? | Very specific, different legume different rhizobium |
| Outline the early steps of nodule formation | Recoginition of partner Root hair curling Infection thread Induction of cortical division |
| Stages of root formation after infection thread | Rhizobia travels to cortex Release of bacteria into plant cytoplasm (endosymbiosis) Formation of bacteroids |
| Bacteriod | Swollen mishapen cells that can fix nitrogen |
| Peribacteroid membrane | Membrane developing symbiosomes |
| What does the legumes produce in exudate to signal the right rhizobium? | Three ring aromatic compounds called flavanoids |
| What does signals the plant to start root hair curling? | Nod factors |
| NOD genes | Borne of accesory genetic elements Sym plasmids in rhizobium and sinorhizobium Chromosomal symbiosis islands in mesorhizobium loti |
| Mesorhizobium loti | Rhizobium for genus lotus In chromosome Shown to share this DNA |
| The mesorhizobium island | Chromosomally intergrated element Converts non symbionants to symbioants through conjugation |
| What genes are needed for conjugation? | OriT, Trb, tra |
| Model for symbiosis island transfer | Excision from a transient circular intermediate, single stranded transfer through mating pore, rolling circle replication. Second strand synthesis in recipient and replacement in donor. |
| Regulatory nod genes | The nodD gene product turns on other nod genes in response to flavanoid lignal from plant |
| Structural nod genes | Synthesise lipochitooligosacchride signalling molecule called nod factor |
| Plant response to Nod factors | Influx of calcium at root hair tip calcium spiking at root hair nucleus Curling of root hair intiation of cortical division Nod factors share many characteristics with plant hormones but active at 10^-11 Mcf |
| How do plant receive Nod factors? | NFR1 and NFR2 work together to bind nod factor on there LysM domain causing a signal cascade |
| What rhizobium genes are essential for symbiosis | Nif and fix |
| Nitrogen fixing reaction | N2 + 8H+ + 8e- ----> 2NH3 + H2 Nitrogenase enzyme |
| What is the minimum ATP for Nitrogen fixing? | 16 |
| What is the nitrogenase enzyme inactivated by? | O2 |
| What can inhibit transcription of nif and fix? | High O2 levels |
| Bacteriods electron transport chain is... | High affinity for O2 |
| What is the role of leghaemoglobin | To facilitate diffusion of O2 at a high flux and low conc |
| What does the host plant supply the bacteroid with for energy? | C4 - dicarboxylic acids |
| Dct | Gene for transport of c4 carboxylic acids |
| Ammonia assimilation | NH3 enters host cytosol by diffusion Glutamine synthetase and glutamate synthetase to make amides |
| Function of FixL and FixJ system | Regulates genes in response to molecular oxygen |
| FixL | Sensor tethered to the membrane Contains an intracellular oxygen sensing heme domain |
| What occurs with FixJ and FixL in presence of oxygen? | FixJ senses oxygen and dephosphorylates FixJ and target genes are turned off |
| What happens with FixJ and FixL when no oxygen are around | In the absence of oxygen FixL kinease phosphorylates Fix which activates a signal tat turns target genes on |
| Mycorrhiza | Root fungus |
| What are the benefits of the mychorrhizal symbiosis? | Derives carbohydrates Contributes nitrogen, phosphate and water Increases surface area tapped by roots |
| How widespread is mycorrhiza | >90% of land plants have it |
| Ectomycorrhizae | No intercellular penetration |
| Endomycorrhizae | Fungal mycelia penetrate root cells |
| Where is ectomycorrhizae found? | Forest trees, beach, oak etc |
| What does ectomycorrhizae form? | A sheath around root and a hartig net |
| The two types of Endomycorrhizae | Endotrophic and arbuscular (AM) |
| Endotrophic | Characterised by non pathogen penetration of root cortex by sparate hyphae that often form intracellular coils |
| Orchids | Obligate mycorrhizal fungus Partially pathogenic balance between mutualism and parasitism Orchids produce orchinol to keep fungal in check |
| Arbuscular | Most common type found in most crops Inter and intracellular non separate hyphae |
| PAM | A periarbuscular membrane that surrounds each fungal hyphae and excludes it from the cytoplasm |
| PAS | Periarbuscular space, the space between the fungal plasma membrane and the PAM |
| Strigolactones | Cause spore germination and hyphal branching and increase physiological activity in the fungal spores and hyphae |
| Myc | Mycorhizzal factors Induce calcium oscilialations in root epidermidal cells and induce plant symbiosis genes |
| PPA | Prepenetrational apparatus Fungal hyphae enters the apoplast where it branches and grows laterally |
| What does hyphae induce in inner cortical cells? | PPA like structures for the branches to form arbusules |
| What kind of molecule is Myc | Lipochitooligosacchride |
| What is the link between rhizobium and mycorrhizae? | They both have a LysM like receptor Think rhizobium probably recruited the system from mycorrhizae |
| Benefits of mycorrhizae | Essential in nutrient poor environments Increased surface area root availability provided by mycelia Resistance to drought stress Protection from some pathogens link plants into a community that shares nutrients and colonises multiple species |
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