Bio 201 S12 Lect 12(True v2

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Unformatted text preview: hers •  fresh water: mainly cyanobacteria •  land: various soil bacteria (small amounts); N- fixing bacteria living in associa<on with plant roots (MUTUALISM) –  the majority of soil N •  plants get fixed N (ammonium); bacteria get high energy carbon compounds (plant photosynthe<c products) •  most well known: Rhizobium, mutualist of legumes (beans, alfalfa, clover, etc.); infec<ons form nodules in plant roots –  used in crop rota<on •  other associa<ons for N fixa<on –  lichens: fungi + N- fixing cyanobacteria (these bacteria also fix N in fems, cycads, nonvascular plants] –  rice: can be grown in flooded fields with the water fern Azolla, mutualist with a N- fixing cyanobacteria –  woody plants (alder, lilac) associate with N- fixing filamentous ac<nobacteria nitrogen fixing reac<ons •  three requirements: –  strong reducing agent - > transfers H to N2 and intermediate products •  (can be provided by photosynthesis or respira<on, depending on species) –  energy: ATP –  nitrogenase enzyme (catalyst of the reac<on) •  inhibited by oxygen; many nitrogen fixing bacteria are anaerobic •  root nodules maintain a low O2 environment (respira<on s<ll possible; nitrogenase is not inhibited) •  in nodules, plants use leghemoglobin (pink color visible if high enough concentra<on) to transport O2 (molecule is an evolu<onary rela<ve of hemoglobin) - contains iron heme component plant- bacteria symbiosis: absolutely necessary for N fixa<on to take place in nature • need communica<on for nodule to form (flavinoids from root cause bacteria to transcribe nod genes) • need O2- free interior of nodule - depends on leghemoglobin transport of O2 • need bacteria to form bacteroids (highly specialized morphology for N fixa<on) • analogous to (and may involve some of the same genes as) mycorrhizal fungal associa<ons with plant roots global nitrogen cycle nitrate nitrite carnivorous plants •  usually found in N deficient habitats (e.g. bogs) •  evolved to gain nutri<on (N) from animal <ssues •  venus fly traps (dicot) – –  specialized leaves triggered to close by hairs •  pitcher plants (dicot) – –  aPract insects by colors and scents; downward poin<ng hairs on steep sides prevent insects from escaping •  sundews (dicot) – –  hairs secrete s<cky sugar solu<on; insects are aPracted and get stuck •  these plants don't absolutely need to eat insects, but grow faster and perform more photosynthesis when hPp:// they do gallery2/v/Tropicalia/lady_s +slipper+orchid.jpg.html? g2_GALLERYSID=85bdf00ed9398 484c34cffdb21a22e7a...
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This note was uploaded on 10/02/2013 for the course BIO 201 taught by Professor True during the Spring '08 term at SUNY Stony Brook.

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