Comparable shoot mineral concentrations in tobacco
plants, whether mycorrhizal or not, were possibly due to
the high availability of nutrients supplied along with the
nutrient solution in this experiment. As in previous studies
using N. tabacum and the same fungal species used here
(Fester et al. 1999; Janouskova et al. 2007), the roots were
highly colonised by G. intraradices and vesicles, arbuscules and abundant extra- and intraradical hyphae were
observed. Thus, despite the high rate of colonisation,
positive effects on growth and nutrient uptake were not
observed. This ‘‘unresponsiveness’’ to AM inoculation may
be related to a phosphorus/carbon imbalance between the
symbionts, as the experimental condition of irrigation with
a nutrient solution may have minimised the positive
mycorrhizal response on plant growth (Smith et al. 2011).
Tobacco is a classic example of a plant that synthesises
specialized metabolites in its roots, which are transported
to the shoots where they will play a role in plant defence
(Erb et al. 2008). In tobacco, the synthesis of the main PAs
in roots and their concentration in the leaves may increase
in response to different mechanical, chemical or biotic
stressors (Baldwin et al. 1994; Shi et al. 2006; Steppuhn
Comparable shoot mineral concentrations in tobacco
plants, whether mycorrhizal or not, were possibly due to
the high availability of nutrients supplied along with the
nutrient solution in this experiment. As in previous studies
using N. tabacum and the same fungal species used here
(Fester et al. 1999; Janouskova et al. 2007), the roots were
highly colonised by G. intraradices and vesicles, arbuscules and abundant extra- and intraradical hyphae were
observed. Thus, despite the high rate of colonisation,
positive effects on growth and nutrient uptake were not
observed. This ‘‘unresponsiveness’’ to AM inoculation may
be related to a phosphorus/carbon imbalance between the
symbionts, as the experimental condition of irrigation with
a nutrient solution may have minimised the positive
mycorrhizal response on plant growth (Smith et al. 2011).
Tobacco is a classic example of a plant that synthesises
specialized metabolites in its roots, which are transported
to the shoots where they will play a role in plant defence
(Erb et al. 2008). In tobacco, the synthesis of the main PAs
in roots and their concentration in the leaves may increase
in response to different mechanical, chemical or biotic
stressors (Baldwin et al. 1994; Shi et al. 2006; Steppuhn
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