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(a)
(b)
(c)
(d)
NS
S
NS
S
FIGURE 6.1 Growth of rice seedlings: nonsymbiotic (NS) on left and symbiotic (S) on
right, shown over an 8-day period. a = day 0; b = day 2; c = day 4; d = day 8. Germinated
seeds were placed on top of an agarose medium that was poured between two glass plates and
were then grown under constant light for 8 days at 22°C (daylight balanced fluorescent bulbs,
22 µmol m -2 s -1 ). S-seedling roots grew more rapidly and developed root hairs earlier than NS
seedlings. Preparation of the endophyte ( F. culmorum ) and plant inoculations are described
in Rodriguez et al. (2009a).
selected fungi have more tolerance of drought and salinity stress (Rodriguez et al.
2008; Redman et al. 2011).
Current research is examining how endophytes can increase plant growth rate
and biomass while decreasing water consumption. Although the genetic and bio-
chemical mechanisms for these symbiotic benefits are not yet established, there
are several possible explanations, including fungal-generated or fungal-induced
plant hormones, increased metabolic efficiency, decreased metabolic rates, and/or
enhanced photosynthesis.
Many fungi are known to produce plant hormones that regulate plant growth,
development, and water relations (Chung et al. 2003; Bomke et al. 2009; Tsavkelova
et al. 2012). Our own studies have demonstrated that fungal endophytes produce
substantial amounts of indole acetic acid (IAA) in culture. However, documenta-
tion of fungal-produced plant hormones in planta is limited, so it is not yet possible
to determine the significance of fungal-derived hormones with regard to symbiotic
benefits. For some initial work regarding phytohormone-induced tolerance of salin-
ity, see Khan et al. (2012).
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