Effect of Gibberellic Acid and Salinity on Growth and Endogenous Growth Hormones of Soybean Cultivar Hwangkeum.

Our study is based on changes in growth, endogenous gibberellins (GA), jasmonic acid (JA) and salicylic acid (SA) levels of soybean cultivar Hwangkeum in response to elevated levels of gibberellic acid (GA₃) alone or in combination with salinity stress. Furthermore, the role of GA₃ on salinity alleviation was also investigated. We found that plant growth (height, fresh weight and dry weight) was significantly enhanced by the application of elevated GA₃ level but was markedly reduced by NaCl as compared to control. Elevated level of GA₃ significantly enhanced growth of soybean under salt stress condition. The chlorophyll contents were found less affected by GA₃ and NaCl application. Endogenous GA contents were analyzed through high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM), JA with GC-MS-SIM, while SA with HPLC. These plant hormones were analyzed in 14 days old soybean seedlings, which were subjected to different levels of GA₃ and NaCl stress for 24 h. The GA analysis showed that both early C-13 hydroxylation and non C-13 hydroxylation was functional in soybean. The major GA biosynthesis pathway operated in soybean was identified as early C-13 hydroxylation that synthesizes bioactive GA_4. It was also observed that endogenous GA content increased with GA₃ application and higher levels of endogenous GA was recorded for GA₃+NaCl supplied plants than sole NaCl applied treatments. JA content of soybean increased with elevated GA₃ level, although the level of endogenous JA was higher in JA+NaCl applied treatments than single application of GA₃ or NaCl_.  SA level increased with 0.5uM and 1uM GA₃ but reduced in soybean plants that were subjected to 5uM of GA_3.  SA contents also significantly increased in GA₃+NaCl applied treatments. It was thus concluded that GA₃ application significantly enhanced growth of soybean and alleviated NaCl induced salt stress.