"Epiparasitic plants specialized on arbuscular mycorrhizal fungi"
I. Bidartondo (1)*, Dirk
Redecker (2)*, Isabelle
Nature 419, 389-392 (2002)
(1) Department of Plant & Microbial Biology, University
of California, Berkeley, California 94720-3102, USA
Plants normally obtain their carbohydrates (sugars, starch
etc.) by photosynthesis from carbon dioxide in the atmosphere
(autotrophic lifestyle). Other organisms (humans, animals,
fungi, many bacteria) need these carbohydrates because they cannot
produce them from carbon dioxide, they are heterotrophic.
Some of these non-photosynthetic plants form specialized organs
(haustoria) to directly get nutrients from their victims. However,
others do not have such obvious organs. For some of these it
has been shown that they exploit fungi who live in a symbiosis
with green plants, which is known as mycorrhiza. In a mycorrhiza
(="fungus-root"), fungi colonize the roots of and
obtains carbohydrates from the plant. In return the fungus acts
as an extended root system and provides mineral nutrients (e.g.
phosphate, nitrate, ammonium) to the plant. This relationship
is beneficial for both partners and therefore very widespread
among plants. Plants without mycorrhiza are the exception. Some
heterotrophic plants have fungi in their roots, which are connected
to nearby green plants. These plants are known as mycoheterotrophs.
They obtain their nutrients from the green plants via these fungal
bridges. By cheating the fungi they indirectly parasitize those
autotrophic plants and are called "epiparasites".
There are some rather widely known mycoheterotrophic plants,
such as some non-green orchids and plants from the family Monotropaceae.
Those plants get their nutrients from a type of mycorrhiza known
as ectomycorrhiza. This symbiosis typically occurs mainly
between trees and some groups of fungi. Some of these fungi form
fruitbodies which are visible with the bare eye ("mushrooms").
A different type of mycorrhiza, arbuscular mycorrhiza,
is much more widespread. It is found in majority of herbaceous
plants, but also in many trees in the tropics. Many important
crops are among the hosts. Exceptions are e.g. cabbage, rapeseed
and spinach. The fungal partners are less well-known fungi (Glomeromycota)
which do not form mushrooms, but spores which are visible under
It has been suggested that arbuscular mycorrhizal fungi may also be cheated by some non-green plants, but conclusive proof has been lacking. It has also been thought that there is a very low host specificity in arbuscular mycorrhiza, meaning that in principle every fungus can colonize every plant
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