Endophytic Fungi: Diversity, Characterization and Biocontrol

Dark Septate Endophytes (DSE) in Polluted Areas 129

complex compounds. However, these compounds can still take part on

the cell’s metabolism and thus remain potentially toxic.

 Vacuole compartmentalization: transport inside vacuoles reduces the

concentration of certain toxic metals by retention inside the vacuole.

 Biotransformation: set of decomposition, conjugation or synthesis

reactions involved in the proper processing of the contaminant.

 Cellular repair mechanisms: mechanisms in response to the

deterioration suffered aiming to re-establish the plant native

characteristics.

 Presence of mycorrhizas: plants with mycorrhizal fungi have a higher

tolerance to heavy metals, mainly due to their ability to immobilize

them at the root, preventing them from reaching the aerial part.

The latter point opens the door to the possible use of several fungal
species in what has been called mycoremediation programs.

FUNGAL ROLE

Some of the most paramount interactions between plants and the
environment occur within and around soils, such as nutrient and element
uptake, environmental toxicity due to pollution, root diseases and soil
formation. In most cases, fungi mediate these interactions. There are many
studies on metal tolerance in plants and metal-tolerant cultivars. However,
only few have taken into consideration the importance of mycorrhizal fungi in
plants from polluted areas, and even less in forest species.
Numerous studies have shown the accumulating capacity of heavy metals
by the fruiting bodies of different species of mycorrhizal and saprophytic fungi
(Garcia et al., 2009; Michelot et al., 1998; Kalač, 2010). This capability is
known as bio-absorption and has been defined by Shumate and Strandberg
(1985) as a series of undirected physicochemical mechanisms that can occur
between different species of metals and cellular components of various
biological species. Biological uptake by fungi can be divided into three
categories (Danesh et al., 2013): (1) Capture by binding to specific sites on the
cell structure, (2) intracellular uptake and (3) chemical transformation. The last
two are made by living cells and involve an active uptake, so it could be called
bioaccumulation (Kapoor et al., 1999).