Biomedical Engineering Reference
In-Depth Information
(Danneberg et al. 1992). AM symbiosis resulted in the inhibition of two
pathogenesis genes expression and enhanced levels of zeatin riboside like
cytokinins (Ginzberg et al. 1998). These indicate some of the interesting
effects of AM symbiosis on controlling pathogens.
In addition, cytokinins are able to upregulate early nodulation genes
(van Rhijn et al. 1997). However, it remains to be investigated that whether
the plant or fungal productions are involved in the alteration of cytokinins.
It is suggested that enhanced P uptake of mycorrhizal plants can increase
cytokinins production in the roots. Increased ratios of cytokinins may
enhance shoot growth and not root growth.
Glomus mosseae
is able to
produce two gibberellin like products (Hause et al. 2007).
Ethylene
Ethylene is the stress hormone, controlling plant growth interactively with
the other plant hormone ABA. Under stress the amounts of ethylene in
plant increases adversely affecting plant growth. Hence, by controlling
the rate of ethylene production in plant the unfavorable effects of stress
on plant growth can be alleviated. For example, plant growth promoting
rhizobacteria are able to produce the enzyme 1-aminocyclopropane-1-
carboxylate (ACC)-deaminase, which is able to turn ACC, the prerequisite
for ethylene production, into ammonia and α-ketobutyrate (Glick 2005,
Jalili et al. 2009). It has also been indicated that ethylene can signifi cantly
decrease the rate of AM colonization, especially under P deficient
conditions (Zsögön et al. 2008). Hence, soil and plant nutritional balance
is a very important factor determining the effectiveness of plant hormones
on the AM symbiosis.
Addition of 5.5 mg/l ethylene altered root morphology and
substantially decreased root colonization of
Pisum sativum
. Although the
number of appressoria (the fungal part, which helps the fungi enter the
root cortical cells) remained unaffected, the altered shape of appressoria
decreased the inoculation ability of fungi. Hence, it is likely that the signal
perception by appressoria can affect its growth and development, which
is also affected differently by different plant hormones. These effects were
concentration dependent and while at higher concentrations (0.6 µl/l)
ethylene decreased root and shoot growth and mycorrhizal colonization,
concentration of 0.3 µl/l decreased root length but not root colonization
(Abeles et al. 1992) indicating that the adverse effects of ethylene on
plant roots is more pronounced than on the interactions between the two
symbionts as indicated in the following.
The biosynthesis of ethylene is reduced due to the production of phenolic
products in the roots of
Solanum toberosum
, resulting in the development of
symbiosis (McArthur and Knowles 1992). After the complete development
