Effect of silicon on some of morphological. physiological parameters and the expression of betaine aldehyde dehydrogenase and proline 5-carboxylate synthase genes in Iranian Borago medicinal plant under drought stress

Drought is one of the most important growth limiting factors in plants. The great extent of drought-prone land and the scarcity of water resources have drawn much attention to drought related issues. In this study, in order to investigate the effect of silicone on some morphological, physiological and molecular characteristics of Iranian Borago under drought stress conditions, a factorial experiment was conducted in a completely randomized design with 3 replications. For this purpose, 14-day-old Borago seedlings were treated with silicone (0, 0.5 and 1.5 mM) and drought (with polyethylene glycol at three concentrations of 0, 9 and 12%) under hydroponic conditions. Morphological and physiological parameters were evaluated 5 weeks after treatment. The results showed that drought significantly reduced the growth parameters, chlorophyll a, total chlorophyll and carotenoids contents compared to the control. Silicon treatment reduced the negative effects of drought stress and increased growth parameters and photosynthetic pigments. Also, drought stress caused significant increase in anthocyanin, carbohydrates (soluble and reducing sugar), glycine betaine, proline contents, and increased expression of BADH and P5CS genes. Combined drought and silicon treatments significantly reduced the expression of BADH and P5CS genes and the products of these two genes, proline and glycine betaine, in comparison to drought stress samples, which confirms the role of silicon in reducing osmotic stress in the present study.