Chapters 27 & 28

fungus

root

a close association b/w two unlike organisms that is beneficial to one or both of them

mutualistic bacteria; produce nodules on host plants in legume family; fix N2 into a useable form for plants (NH4); alpha proteobacteria; carry Sym plasmid

mutualistic fungi; live in close association w/ plant roots; extend surgace area and length of roots; protection from disease and toxins

when two organisms “work together”; both benefit from relationship

how do mycorrhizae help plants? how do the fungi benefit?

endomycorrhizae: grow inside plant cells; most common type = Arbuscular Mycorrhizae (AM); form on most Angiosperms ectomycorrhizae: grow around and b/w plant cells (outside); mostly form on trees

• rhizobia are attracted to flavonoids • rhizobia attach to root hair • an infection thread forms, bacteria enter root cells • bactera –> bacteriods; packed root cells enlarge • enlarged root cells form a nodule

genes for host-specific nodulation and for N fixation genes

vegetative part of a fungus colony; consisting of a mass of branching, thread-like hyphae

plants, most trees; can degrade complex organic matter; live in soil as saprotrophs; most trees are **obligately ectomycorrhizal **(need them to survive)