Lecture notes 13

Partner give up to 90 of photosynthate to fungal

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Unformatted text preview: rs •  Trebouxia –  Most common genus associated with lichen partnerships –  Single ­celled rarely found as free ­living –  Found in temperate regions •  Trentepohlia –  Found in tropical regions Cyanobacteria Lichen Partners •  Found in about 10% of lichens •  Pel9gera –  Most common genus –  Found in dog lichen •  Some lichens have green algae & cyanobacteria •  Cephalodia – wart ­like structures on lichen surface –  Thought to use nitrogen fixing abili8es of cyanobacteria Forms of Lichens •  Lichen thallus – body of lichen •  Categories –  Foliose •  Flat & leaf ­like –  Fru8cose •  Erect & branch ­like –  Squamulose •  Small & scale ­like –  Crustose •  Flat & crust ­like 6 11/23/09 Structural OrganizaUon •  Many have well ­defined structures •  Typical structure –  Upper cortex –  Medulla –  Lower cortex –  Rhizinae •  Algal associa8ons also require gas exchange Physiology: Water Requirements •  Lack of water –  Lichens containing green algae absorb water from humid air & resume photosynthesis –  Lichens containing cyanobacteria must absorb liquid water to resume photosynthesis –  Drought tolerance is likely conferred by hydrophobins produced by lichen fungi –  Hydrophobin coated fungal hyphae create spaces for gas exchange Physiology: Nutrient Exchange Physiology: Nutrient Exchange •  Lichen fungi protect photosynthe8c partner & absorb nutrients •  Photosynthe8c partners provide sugars for the growth of lichen –  Very efficient at absorbing nutrients from limited environmental resources –  Unfortunately for lichens, also absorb toxins &...
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