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3.6 Omic Analysis of Plant Response to Combined
High-Salinity and Elevated CO 2 Perturbations
Despite the fact that physiological measurements in different plants and trees have
indicated that the elevated CO 2 conditions can alleviate the negative effect of salinity
stress in plants at least for short-term treatments (Geissler et al. 2010 ; Perez-Lopez
et al. 2012 ; Perez-Lopez et al. 2009 ; Ratnakumar et al. 2013 ; Takagi et al. 2009 ), to
the best of our knowledge, there has currently been only one study, which has moni-
tored the molecular response of the plants to combined salinity stress and elevated
CO 2 , using the high-throughput biomolecular (omic) analyses. Kanani et al. ( 2010 )
integrated GC-MS metabolomics and DNA microarray transcriptomics to study the
growth of A. thaliana plant liquid cultures in a high-salinity (i.e., 50 mM NaCl) me-
dium and elevated CO 2 (10,000 ppm) environment, for the first 30 h of continuous
treatment in a time-series experiment. The plants had grown under constant light,
temperature, and humidity and the same conditions were maintained throughout the
treatment period. The authors support this setup, as it minimizes any contributions
to the observed physiological changes from any other parameter but the two inves-
tigated factors. The authors report that the effect of the salinity stress was stronger
than that of the elevated CO 2 conditions at both the transcriptional and metabolic
levels. Interestingly, there was a strong similarity over time between the transcrip-
tomic responses of the plants exposed to high salinity and those exposed to the
combined stress. This similarity suggests that the early transcriptional response of
the plant cultures to the salinity stress is robustly active independently of the co-oc-
currence of the elevated CO 2 conditions. For example, the SOS signaling pathway
is upregulated at the transcriptional level under both high-salinity and the combined
perturbation conditions. The major finding of this analysis, however, was that the
observed physiological consequences of the combined stress at the metabolic level
was different from what would have been expected based only on the transcriptomic
profiles. Specifically, the combinatorial effect of the elevated CO 2 conditions and
the salinity stress on the metabolic physiology of the plants was milder than that of
the salinity stress alone, implying that the elevated CO 2 conditions are an alleviat-
ing factor for the salt-stressed samples. The analysis of the metabolomic profiles
indicated that this beneficiary role of the elevated CO 2 can be primarily attributed
to the provision of additional resources to the salt-stressed plants. Using these ad-
ditional resources the plants can activate their response machinery against high sa-
linity and produce osmoprotectants and antioxidants, without having, however, to
sacrifice substrates needed for plant growth. This conclusion was based on the fact
that, under the combined stress, the concentrations of the TCA cycle intermediates
citrate, aconitate, and isocitrate, and the amino acids alanine, valine, lysine, and
asparagine, which contribute to protein synthesis, were observed at similar values
as in the control metabolic state. At the same time, metabolic precursors of osmo-
protectants that exhibited increased concentration in the salt-stressed plants (i.e.,
S-adenosyl-methionine and glycine, which are precursors of glycine–betaine and
β-alanine, which is a precursor of β-alanine-betaine) retained their concentrations
in the plants subjected to the combined high- salinity and elevated CO 2 perturbation.
M.-E. P. Papadimitropoulos and M. I. Klapa