Physiological and molecular insights into the high salinity tolerance of Pongamia pinnata (L.) pierre, a potential biofuel tree species

Abstract

Soil salinity is gradually becoming a threat to the global economy by affecting agricultural productivity worldwide. Here, we analyze the salinity tolerance of Pongamia pinnata with an insight into the underlying physiological and molecular responses. Despite a reduction in net photosynthetic rate, P. pinnata efficiently maintained its leaf water potentials even at 500 mM NaCl for 15 days and displayed no visible stress symptoms. Na+ localization analysis using CoroNa-Green AM revealed effective Na+ sequestration in the roots when compared to leaves. Elemental analysis demonstrated that roots accumulated more of Na+ while K+ content was higher in leaves. At the molecular level, salt stress significantly induced the expression levels of salt overly sensitive1 (SOS1), SOS2, SOS3, high affinity K+ transporter (HKT1), ABA biosynthetic and receptor genes (NCED and PYL4), guaiacol peroxidase (POD) exclusively in roots while tonoplast localized Na+/H+ exchanger (NHX1) was significantly enhanced in leaves. Our results clearly demonstrate that leaves and roots of Pongamia exhibit differential responses under salt stress although roots are more efficient in sequestering the Na+ ions. The present study provides crucial inputs for understanding salt tolerance in a tree species which can be further utilized for developing salt tolerance in higher plants.