Biomedical Engineering Reference
In-Depth Information
of symbiosis, enhanced P uptake may inhibit such effects and hence limit
the further development of AM symbiosis (Hause et al. 2007). This may
indicate the interesting aspect related to the specifi city of mycorrhizal
symbiosis. In other words plants that are more symbiotic to AM produce
some products that can result in the higher activation of AM symbiotic
genes. Such products may also control the level of parameters that inhibit
AM symbiosis such as ethylene production (Riedel et al. 2008). Accordingly,
non-host plants produce products, which have direct unfavorable effects
on the symbiosis process or can indirectly affect the symbiosis process as
mentioned. This indicates that it may be likely to control the adverse effects
of soil stresses on mycorrhizal symbiosis through controlling the level of
stress hormones in the host plant.
ABA
ABA is necessary for the colonization of plant host roots by AM fungi and
it controls the formation of arbuscules (Herrera-Medina et al. 2007). AM
fungi and ABA induce the activities of genes necessary for the production
of leghemoglobin. The latter can detoxify the unfavorable effects of nitric
oxide by binding to it in mycorrhizal roots, in the symbiotic nodules and
under non-symbiotic conditions. Furthermore, nitric oxide is necessary
for ABA production signaling under stress and hence leghemoglobin
can control the mechanisms necessary for the regulation of ABA related
processes (Ruan et al. 2004, Veiweg et al., 2005, Grunwald et al., 2009).
However, Zsögön et al. (2008) indicated that ABA did not infl uence the
colonization process. Interestingly, under drought stress the elevated level
of ABA in mycorrhizal plants can induce the stress responsive genes in
the plant resulting in the enhanced root hydraulic activity and decreased
plant transpiration (Aroca et al. 2008).
ABA production increased in the roots of mycorrhizal corn (
Zea mays
L.) (Danneberg et al. 1992, Bothe et al. 1994) and soybean (
Glycine max
L.) (Meixner et al. 2005). This increase has also been found in the shoots
indicating the existence of a controlling mechanism, which adjusts the rate
of ABA in different parts of the plant during the symbiosis (Meixner et al.
2005). ABA reduction has also been observed in plant shoot, suggesting
the role of AM fungi in improving the plant water balance under drought
stress as ABA is able to control the activities of guard cells surrounding the
stomata (Hause et al. 2007).
IAA
Alterations in the properties of mycorrhizal roots, including increased
number of lateral/fi ne roots, during the early period of plant growth
