The correlation analysis between metabolites provides new
insights for salinity studies in Pongmaia
In leaves, a strong correlation was observed among carbohydrates, fatty
acids and polyols in treated plants suggesting that these metabolites
may serve as first line ‘osmolyte defense’ against Na+ion osmotic imbalance, protecting the structural and functional
integrity of the cell and cell membrane from osmotic imbalance (Gao et
al., 2013; Conde et al., 2015) (Figure 7). Further, the positive
interaction between carbohydrates, intermediates of TCA cycle and
polyols could serve as second line ‘ion homeostasis defense’ to maintain
the intracellular pH and ion balance under salt stress (Guo et al.,
2015) (Figure 7). The positive correlation, observed between
carbohydrates, polyols, amino acids and organic acids might serve as
third line ‘quick energy defense’ suggesting an anaplerotic role for the
TCA cycle and provide immediate carbon energy source under salt stress
(Zhang et al., 2017). The association between carbohydrates and amino
acids showed maintain C:N balance, which may ameliorate salt-induced
stress in Pongamia (Nasir et al., 2010;Naliwajski & Skłodowska, 2018).
In roots, the positive correlation between organic acids, carbohydrates
and fatty acids may serve as line of ‘ion homeostasis and osmolyte
defense’, regulating cellular pH, osmotic potential and membrane
fluidity (Sakamoto & Murata, 2002; Guo et al., 2015). The enhanced
correlation of secondary metabolites with these metabolites could serves
as second line of ‘antioxidant and cell wall barrier defense’, where it
enhances the tolerance to salinity by regulating pathways such as ROS
detoxification and cell wall barrier synthesis (lignin biosynthesis)
(Liu et al., 2018; Yang et al., 2018) (Figure 7). The positive
association of polyols may provide a continuous osmoticum at cellular
level to mitigate the osmotic imbalance raised by the increase uptake of
Na+ ions into the vacuole (Slama et al., 2015).