Comparative Effects of Gibberellin and Paclobutrazol on Na and K Content, Phenolic Compounds and the Activity of Some Enzymesin its Biosynthesis Pathway in Sweet Sorghum (Sorghum bicolor) under Salt Stress

Salinity is one of the most important restricting factors for plant growth and production around the world. The use of plant growth regulators has been expanded for improving salt tolerance in recent decades. In this investigation the effect of gibberellic acid (GA) and paclobutrazol (GA inhibitors) were evaluated for ameliorating negative effects of salt stress in sweet sorghum. After germination, the plants in 4 levels of salinity were cultured in Hoagland solution then seedlings were treated by GA and paclobutrazol (PBZ) for 12 days. The results showed that the highest level of salinity without hormone treatment reduced the fresh and dry shoot weight by 44 and 22%, respectively, and increased the fresh (46%) and dry (16%) root weight. Treating Plants with 17 Mm GA and PBZ led to improvement of the above traits in the
salt–stricken plants. PBZ treatment decreased negative effects of salinity and increased potassium (K) content in roots and its transfer from root to shoot. Whereas, translocation factor of sodium was increased about 39% by GA treatment at the presence of 150mM salt. PBZ enhanced phenol content in shoots by increasing PAL activity. Therefore, GA and PBZ improved salt tolerance by transferring some ions toward shoot and root respectively. It seemed that, PBZ has an effective role in salt resistance by increasing of root growth, phenol content and maintaining the ionic balance.