Influence of Salicylic Acid on Morphological and Biochemical Traits in Grape Plantlets in vitro under Heat Stress

Heat stress limits growth and productivity of plants. In this study, the effects of salicylic acid (SA) (0, 10 and 20 μM) on growth, biochemical traits (photosynthetic pigments, reducing sugars, malondialdehydes, other aldehydes, hydrogen peroxides and total proteins) and the activity of antioxidants enzymes (catalase, guiacol peroxidase and ascorbate peroxidase) in shoot and root; and also the survival rate of grape plantlets (cv. ‘Yaghooti’) under in vitro heat stress (25 and 40˚C) were investigated. At 25˚C, SA increased the level of hydrogen peroxides and had negative effects on growth, with the more sever effect at 20 μM. Heat stress (40˚C) reduced growth traits but increased the most biochemical parameters and the activity of antioxidant enzymes in shoot and root. Under heat stress, both levels of SA, especially 20 μM improved all measured parameters by reducing the hydrogen peroxidase level. However, under heat stress, SA treated plantlets survived, whereas all control plantlets died. It is concluded that SA can profoundly improve heat stress tolerance of grape plantlets under in vitro condition.