Physico-biochemical and molecular responses of Acacia auriculiformis to salinity stress

Salinity limits the growth and yield of many crops across the globe and is considered as major threat to agriculture. Acacia auriculiformis, an important salt tolerant crop, is growing abundantly in the salt-affected mangrove areas of Sunderban, West Bengal, India. In the present study, we have reported the physiological, molecular and antioxidant response of this crop to a gradient of salt treatments ranging between 0 and 800 mM NaCl. As a stress response, the antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPX) were highly activated at 200, 400 and 800 mM NaCl respectively. Antioxidant metabolites such as phenols and thiols elevated with increasing salt treatments thus augmenting antioxidant activity with significant positive relationship with phenol content. Similarly, phenylalanine ammonia lyase (PAL) activity was up-regulated in a dose dependent manner with significant relationship with phenol content. This study also reported the phenolic profile for the first time in A. auriculiformis with the abundance of flavonoids. In addition, transcriptional up-regulation of Na+/H+ antiporter gene (NHX1) and the development of robust vascular tissues was noticed at 400 mM NaCl stress compared to control, while further stress at 800 mM NaCl induced poor vascular tissue growth but with higher PAL activity and consequent higher phenol content. Based on this observation, a model for salt tolerance mechanism of A. auriculiformis has been proposed.