Potential objectives for gibberellic acid and paclobutrazol under salt stress in sweet sorghum (Sorghum bicolor [L.] Moench cv. Sofra)

The phytohormones are important in plant adaptation to abiotic and biotic stresses by facilitating a wide range of adaptive responses. Application of gibberellic acid (GA(3)) and paclobutrazol (PBZ) as GA(3) inhibitors have been shown to affect salinity tolerance through modulating phytohormones. The aim of this study was to find out the potential objectives for GA(3) and PBZ as affected by salinity through altering the phytohormones and biochemical parameters in sweet sorghum. Following seed germination, seedlings were cultured in Hoagland nutrient solution containing NaCl supplemented with GA(3) and PBZ for 12 days. The results were analyzed by principal component analysis to identify the best target(s) for salinity, GA(3), and PBZ in sweet sorghum. Paclobutrazol associated with salt improved root/shoot length, carotenoid, and total chlorophyll by modulating cytokinin (CK)/GA(3), indole acetic acid (IAA)/GA(3), and total polyamines/GA(3) ratios. Gibberellic acid-treated plants not exposed to salinity treatments notably improved phytohormones content such as cytokinin, auxin, abscisic acid (ABA), and polyamines resulting in increased stem growth. Moreover, the main objectives of GA(3) were ABA, spermidine, and ABA/GA(3) ratio in response to salinity. Though GA(3) and PBZ have different roles against salt stress, ABA/GA(3) ratio was a similar target of GA(3) and PBZ. This work suggests that altered levels of GA(3) resulting from PBZ- and GA(3)-treated plants cause different allocation patterns in sweet sorghum by regulation of CK/GA(3), IAA/GA(3), and total polyamines/GA(3) ratio. Also, accumulation chlorophyll pigments, carotenoids, and water soluble carbohydrates of sorghum plants under salinity regulated by total polyamines/GA(3) and ABA/GA(3) ratios positively correlated with PBZ application.