Analysis of metabolite pathway in leaf exposed to
O3
The activity of
cytosolic
pyruvate
kinase (PK), NAD-malic enzyme and fumarase in mitochondria were induced
after exposure to ozone (Dizengremel et al ., 1994; Gerantet al ., 1996; Gaucher et al ., 2006; Dizengremel et
al ., 2009). The changed metabolites in tricarboxylic acid (TCA) cycle
under O3 treatment were
isocitrate with increased 2.7 fold
change in rice (Fig. 7, Table S3), 2-oxoglutarate with a reduction of
aproximately 50% and citric of 50% in soybean (Fig. 8, Table S4).
Additionally, O3 treatment leads to the high level of
aspartate-derived asparagine or aspartate in wheat, rice and soybean.
Subsequently, the level of arginine in soybean and agmatine in wheat are
elevated in ornithine cycle. These results suggest that
O3 affects TCA cycle in three crop plants and ornithine
cycle in wheat andsoybean .
In
mevalonate
pathway,
phosphoenolpyruvate
is used for the synthesis of
isoprenoids that play an antioxidant role and prevent photosynthetic
electron transport damage (Loreto & Velikova, 2001; Magel et
al ., 2006; Vickers et al ., 2009). The decreased level of sterols
in wheat but the increased concentration in rice were observed under
O3 stress (Fig. 6 and 7). Moreover, chloric
O3 leads to the declined concentration of fatty acids,
monoteroenes, sesquitepenes, saponins, diterpenes, terpene and
polyterpenes in both wheat and rice. However, all these metabolites were
not changed in soybean in response to O3 (Fig. 8).
Futhermore, in the
glycerol
phosphate pathway and
pentose
phosphate pathway, O3 motivated the synthesis of purines
in the three species, and phospholipids only in wheat and rice. On the
contrary, histidine was up-regulated in soybean, but not changed in
wheat and
rice.The
shikimate pathway is also affected by O3 stress. In
wheat, N-acetyltryptophan was highly accumulated with 10 fold, while
levels of indole alkaloids, methyl salicylate, cinnamic acid, lignin,
phenylpropanoids, flavonoids, and hydroxybenzoic acid were reduced in
various extent (Fig. 6, Table S2). These metabolites are known to be
involved in thickening of cell walls and also act as antimicrobial
compounds (Yogendra et al ., 2015). In rice, metabolites of
cinnamic acid, coumaric acid, flavonoids, salicylate, and indole
alkaloids showed reduced abundance, while phenylalanine and kynurenic
acid were
increased
(Fig. 7). In soybean, several products of
3-(4-hydroxyphenyl)pyruvate,
4-coumarate and flavonoids were reduced but methylsalicylate, lignin,
phenylpropanoids and 4-hydroxybenzoic acid were elevated (Fig. 8).