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In-Depth Information
6 Carbon Dioxide and Endogenous Salicylic Acid Levels
Based on Intergovernmental Panel on Climate Change (IPCC
2007
) predictions,
the atmospheric carbon dioxide (CO
2
) concentration is expected to be double (to
ca. 700 ppm) by the end of 21st century. Thus, it is important to understand what
impact this change will have on plant growth and survival. At present, the effect of
elevating CO
2
levels on endogenous SA biosynthesis is poorly understood. In
plants of tomato that were grown at each of ambient and elevated CO
2
levels, an
infection with root rot (Phytophthora parasitica) gave significant increases in
endogenous SA levels (Jwa and Walling
2001
). However, there was no difference
detected in SA levels between infected plants grown at ambient or elevated CO
2
levels. Even so, plants grown at elevated CO
2
showed an increased degree of
tolerance to inoculation with the pathogen (Jwa and Walling
2001
). In another
system elevated CO
2
levels increased the total (but not free) endogenous SA levels
in tobacco plants and also led to increased resistance against infection by potato
virus Y (Matros et al.
2006
). Elevated CO
2
levels significantly decreased the
endogenous levels of compounds related to SA metabolism, i.e. myo-Inositol and
two hydroxybenzoic acids (m-hydroxybenzoate and p-hydroxybenzoate) in leaves
of rice (Prins et al.
2011
). However, elevating CO
2
had no effect on photosyn-
thesis, photorespiration, leaf C/N ratios or anthocyanin contents (Prins et al.
2011
).
Finally, growing canola plants at elevated levels of CO
2
significantly decreased the
endogenous SA concentrations, relative to canola plants grown at ambient CO
2
levels (Fig.
2
). Furthermore, the decrease in SA levels of the high CO
2
-grown
plants was associated with increased photosynthetic efficiency as well as photo-
synthetic capacity, both relative to plants grown at ambient CO
2
levels (Dahal
et al.
2012
). Elevated ambient CO
2
levels also decreased endogenous ABA levels
in canola leaves (Fig.
2
), though a flush with very high (ca. 50-fold relative to
ambient) CO
2
levels had no effect on endogenous ABA levels in grape leaves
(Loveys et al.
1973
). Growth of Chinese red pine (Pinus tabuliformis Carr.) plants
for prolonged period under elevated CO
2
levels (ca. 2-fold higher than ambient)
significantly decreased endogenous ABA levels in needle tissue (Li et al.
2011
).
Although decreases in endogenous ABA of plants growing at elevated CO
2
may be
beneficial for growth, the decrease in endogenous SA levels could potentially
make plants more susceptible to pathogen attack.
7 Conclusion
To conclude, fluctuations in environmental signals such as light, temperature,
water availability and carbon dioxide concentrations can all influence endogenous
SA levels (Table
1
). However, it does not seem likely, based on the literature we
have reviewed, that environmentally induced changes in plant SA content are a
direct (per se) effect of most environmental fluctuations. Nor does it seem likely
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