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Download Bio 226: Cell and Molecular Biology
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Pathogens • Agrobacterium tumefaciens • Agrobacterium rhizogenes • Pseudomonas syringeae • Pseudomonas aeruginosa • Viroids • DNA viruses • RNA viruses • Fungi • oomycetes • nematodes Symbionts • N-fixers • Endomycorrhizae • Ectomycorrhizae Mineral Nutrition Macronutrients: CHOPKNSCaFeMg • Ca: signaling, middle lamella, cofactor • Fe: cofactor • Mg: cofactor • mobile in plant, so shows first in old leaves Mineral Nutrition Micronutrients: BNaCl others include Cu, Zn, Mn • B: cell elongation. NA metabolism • Na: PEP regeneration, K substitute • Cl: water-splitting, osmotic balance • Cu: cofactor • immobile in plant, so shows first in young leaves Mineral Nutrition Soil nutrients •Amounts & availability vary •Many are immobile, eg P, Fe Mineral Nutrition Nutrients in soil •Plants alter pH @ roots to aid uptake • Also use symbionts • Mycorrhizal fungi help: especially with P Mineral Nutrition Also use symbionts •Mycorrhizal fungi help: especially with P • P travels poorly: fungal hyphae are longer & thinner • Fungi give plants nutrients • Plants feed them sugar • Ectomycorrhizae surround root: only trees, esp. conifers Mineral Nutrition Ectomycorrhizae surround root: trees •release nutrients into apoplast to be taken up by roots Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils Rhizosphere Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils • May deliver nutrients into symplast • Or may release them when arbuscule dies Rhizosphere Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils • Deliver nutrients into symplast or release them when arbuscule dies Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere Rhizosphere Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere • Plants feed them lots of C! Rhizosphere Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere • Plants feed them lots of C! • They help make nutrients available Rhizosphere Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere • Plants feed them lots of C! • They help make nutrients available • N-fixing bacteria supply N to many plant spp N assimilation by N fixers Exclusively performed by prokaryotes Dramatically improve the growth of many plants N assimilation by N fixers Exclusively done by prokaryotes Most are free-living in soil or water N assimilation by N fixers Exclusively done by prokaryotes Most are free-living in soil or water Some form symbioses with plants N assimilation by N fixers Exclusively done by prokaryotes Most are free-living in soil or water Some form symbioses with plants Legumes are best-known, but many others including mosses, ferns, lichens N assimilation by N fixers Exclusively done by prokaryotes Most are free-living in soil or water Some form symbioses with plants Legumes are best-known, but many others including mosses, ferns, lichens Also have associations where N-fixers form films on leaves or roots and are fed by plant N assimilation by N fixers Exclusively done by prokaryotes Also have associations where N-fixers form films on leaves or roots and are fed by plant All must form O2-free environment for nitrogenase N assimilation by N fixers All must form O2-free environment for nitrogenase O2 binds & inactivates electron -transfer sites N assimilation by N fixers O2 binds & inactivates electron -transfer sites Heterocysts lack PSII, have other mechs to lower O2 N assimilation by N fixers Heterocysts lack PSII, have other mechs to lower O2 Nodules have special structure + leghemoglobin to protect from O2 Nodule formation Nodules have special structure + leghemoglobin to protect from O2 Bacteria induce the plant to form nodules Nodule formation Bacteria induce the plant to form nodules 1. Root hairs secrete chemicals that attract N-fixers Nodule formation Bacteria induce the plant to form nodules 1. Root hairs secrete chemicals that attract N-fixers 2. Bacteria secrete Nod factors that induce root hair to coil up. Nod factors determine species-specificity Nodule formation 1. Root hairs secrete chemicals that attract N-fixers 2. Bacteria secrete Nod factors that induce root hair to coil up. Nod factors determine species-specificity 3. Nod factors induce degradation of root cell wall Nodule formation 3. Nod factors induce degradation of root cell wall 4. Plant forms "infection thread"=internal protusion of plasma membrane that grows into cell 5. When reaches end of cell bacteria are released into apoplast and repeat the process on inner cells Nodule formation 5. When reaches end of cell bacteria are released into apoplast and repeat the process on inner cells 6. Cortical cells near xylem form a nodule primordium Nodule formation 5. When reaches end of cell bacteria are released into apoplast and repeat the process on inner cells 6. Cortical cells near xylem form a nodule primordium 7. When bacteria reach these cells the infection thread breaks off, forming vesicles with bacteria inside Nodule formation 7. When bacteria reach these cells the infection thread breaks off, forming vesicles with bacteria inside 8. Vesicles fuse, form the peribacteroid membrane and bacteria differentiate into bacteroids. Nodule formation 8. Vesicles fuse, form the peribacteroid membrane and bacteria differentiate into bacteroids. 9. Plant cells differentiate into nodules Nodule formation 8. Vesicles fuse, form the peribacteroid membrane and bacteria differentiate into bacteroids. 9. Plant cells differentiate into nodules: have layer of cells to exclude O2 & vasculature to exchange nutrients Nodule formation Plant cells differentiate into nodules: have layer of cells to exclude O2 & vasculature to exchange nutrients Complex process that is difficult to engineer: 21 nonlegume plant genera have N-fixers Nitrogen fixation N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi Catalysed by nitrogenase, a very complex enzyme! Nitrogen fixation N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi Catalysed by nitrogenase, a very complex enzyme! Also catalyzes many other reactions Usually assayed by acetylene reduction Nitrogen fixation N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi Usually assayed by acetylene reduction Sequentially adds 2 H per cycle until reach NH3 Nitrogen fixation Sequentially adds 2 H per cycle until reach NH3 May then be exported to cytosol & assimilated by GS/GOGAT or assimilated inside bacteroid Nitrogen fixation Sequentially adds 2 H per cycle until reach NH3 May then be exported to cytosol & assimilated by GS/GOGAT or assimilated inside bacteroid Are then converted to amides or ureides & exported to rest of plant in the xylem! Nutrient uptake Most nutrients are dissolved in water Nutrient uptake Most nutrients are dissolved in water • Enter root through apoplast until hit endodermis Nutrient uptake Most nutrients are dissolved in water • Enter root through apoplast until hit endodermis • Then must cross plasma membrane Crossing membranes A) Diffusion through bilayer B) Difusion through protein pore Selective C) Facilitated diffusion D) Active transport E) Bulk transport Active 1) Exocytosis 2) Endocytosis Nutrient uptake Then must cross plasma membrane • Gases, small uncharged & non-polar molecules diffuse Nutrient uptake Then must cross plasma membrane • Gases, small uncharged & non-polar molecules diffuse down their ∆ [ ] • Important for CO2, auxin & NH3 transport Nutrient uptake Then must cross plasma membrane • Gases, small uncharged & non-polar molecules diffuse down their ∆ [ ] • Polar chems must go through proteins! Selective Transport 1) Channels integral membrane proteins with pore that specific ions diffuse through Selective Transport 1) Channels integral membrane proteins with pore that specific ions diffuse through • depends on size & charge Channels integral membrane proteins with pore that specific ions diffuse through • depends on size & charge • O in selectivity filter bind ion (replace H2O) Channels integral membrane proteins with pore that specific ions diffuse through • depends on size & charge • O in selectivity filter bind ion (replace H2O) • only right one fits Channels O in selectivity filter bind ion (replace H2O) • only right one fits • driving force? electrochemical D
