Different role of gibberellic acid and paclobutrazol on changes of some biochemical and physiological parameters in sweet sorghum under salt stress

The phytohormones are important in plant adaptation to abiotic and biotic stresses by facilitating a wide range of adaptive responses. Application of gibberellic acid (GA3)and Paclobutrazol (PBZ) as GA3 biosynthesis inhibitors have been shown to affect salinity tolerance by modulating phytohormones. The aim of this study was to find out the potential objectives for GA3 and PBZ as affected by salinity by altering the phytohormones, morphological, biochemical and antioxidant parameters in sweet sorghum. So, following seed germination, seedlings were cultured in Hoagland nutrient solution containing NaCl (0, 100 and 200 mM) supplemented with 17 μM GA3 and PBZ for 12 days. The results were analyzed by Principal Component Analysis (PCA) to identify the best target(s) for salinity,GA3, and PBZ in sweet sorghum. Salinity reduced the morphological parameters in shoot and root. Also, the content of photosynthesis pigments increased under salinity stress. The result of this study indicated GA3 and PBZ reduced the negative effect of salt on shoot and root respectively. Paclobutrazol associated with salt improved root/shoot length, carotenoid, and total chlorophyll by modulating cytokinin (CK)/GA3, indole acetic acid (IAA)/GA3, and total polyamines/GA3 ratios. Gibberellic acid-treated plants notably improved phytohormones content such as cytokinin, auxin, abscisic acid (ABA), and polyamines resulting in increased stem growth. Moreover, the main objectives of GA3 were ABA, spermidine, and ABA/GA3 ratio in response to salinity. Though GA3 and PBZ have different roles against salt stress, ABA/GA3 ratio was a similar target of GA3 and PBZ. This work suggests that altered levels of GA3 resulting from PBZand GA3-treated plants cause different allocation patterns in sweet sorghum by regulation of CK/GA3, IAA/GA3, and total polyamines/GA3 ratio.

Keywords:

Abscisic acid , Cytokinin , Chlorophyll , Hormone cross-talk