Environmental Engineering Reference
In-Depth Information
F i g . 1
(
a
-
e
) Arbuscular mycorrhizal colonization in crop
plants. (
a
) Surface runner hyphae (rh) on root of
Allium
cepa
. (
b
) Appressorium (ap) and hyphal entry in
Zea
mays
. (
c
) Intracellular hyphal coils (hc) in
Capsicum ann-
uum
. (
d
) Arbuscules (
a
) and arbuscular trunks (
black
arrows
) in cortical cells of
A. cepa
.
e
Vesicle (
v
) in root of
Z. mays
. Scale bars = 50
ΚΌ
m
Like many host-microbe interactions, the col-
onization process begins with an exchange of sig-
nals between the two partners (host and the
fungus), followed by the development of the
symbiosis. The association is characterized by
the adhesion and ingress of the fungus towards
the host tissue. The host plant provides carbon
source, the photosynthates to the fungus, whereas
in turn, the extraradical hyphae of the fungus
make available the soil nutrients that are not
assessable to plant roots or to the host plant
(Smith and Read
2008
). The colonization of the
root by an AM fungus begins with the fi xation of
the runner hyphae on the rhizoplane of a suscep-
tible host through an appressorium (Fig.
1a, b
).
The AM fungal mycelium has dual phase: extr-
aradical phase characterized by soil hyphae and
intraradical phase characterized by exchange
structures. The former is distinguished morpho-
logically into two types: The fi rst type is the run-
ner hyphae (Fig.
1a
) that actively transport
nutrients and spread the hyphal network across
the rhizospheric region extending the association
to nearby plants (Smith and Read
2008
; Neumann
and George
2010
). The second type is the fi nely
branched fungal hyphae that play an important
role in the uptake of nutrients from the soil.
Intraradical phase consisting of intraradical
hyphae, arbuscules and vesicles (Fig.
1c-e
) plays
an important role in nutrient exchange and uptake
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