Dehydroabietic acid R=COOH (DHA), a naturally occuring diterpene resin acid, is an activator of systemic acquired resistance (SAR) under biotic stress. However, there had been no report on its functioning under salinity. In the present study, we determined the effects of DHA on salinity and its possible role as a signal transmitter in soybean (Glycine max L.) leaves under salinity (200 mM NaCl). Furthermore, physiological parameters, chlorophyll, proline, malondialdehyde (MDA), hydrogen peroxide (H2O2) content, superoxide (O2‾) and hydroxyl radical (•OH) scavenge capacity, as well as antioxidant enzymes (SOD, POX, APX and GST) and GmWRKY-71 gene expressions were investigated in the treated plants at 6 h, 12 h and 24 h. The obtained results showed that pretreatment of DHA caused (1) a reduction in salt-induced damage, (2) improvement in biomass yield, water status, chlorophyll and leaf area, (3) regulation of the proline level and relative electrolyte leakage, (4) increase in reactive oxygen species (ROS) scavenging capacity, (5) induction of SOD and APX enzyme activity at all the investigated periods, while POX only at 6 h, and thus alleviation of the oxidative damage. In addition, the changes in GmWRKY-71 gene expressions were remarkable in soybean under salinity. To sum up, these results showed that DHA can be used as a ROS inhibitor or a signal molecule in increasing salt tolerance in soybean under salinity.

Abstract The purpose of this study was to illuminate the effects of fulvic acid in plants’ stress signaling pathway. 2.0 mg/l fulvic acid was sprayed on soybean leaves for 3 days at 12 h intervals, followed by treatment of 150 mM NaCl or exposed to heat stress at 35°C for 2 h over 2 days. Pre-treatment with fulvic acid increased the relative water content (RWC), antioxidant enzyme, isoenzyme activities (SOD, APX, GST), as well as alleviated the stress-induced oxidative damage by decreasing the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). In addition, the application of fulvic acid under salt stress induced rubisco expression only at 12 h, while it induced the expression of cytochrome c oxidase at 6 h and 12 h. On the other hand, fulvic acid under heat stress induced significant expression of both rubisco and cytochrome c oxidase at 6 h and 12 h. However, under high salinity conditions, fulvic acid suppressed the transcript levels of Hsp70, while it induced increases in Hsp70 levels under heat treatment at 6 h. As a result, in this study, fulvic acid played the role of a regulator and stimulant in stress response of soybean leaves.