In-vitro PHYSIOCHEMICAL RESPONSES OF Viola odorata PLANT TO COMBINED SALT AND DROUGHT STRESS

Abstract

Nowadays sweet violet (Viola odorata) is an ornamental-medical plant that considered as endangered and threatened species. On the other hand, biotic and abiotic stresses impose a major threat to agriculture. Here, we investigated the effects of salinity and drought stresses, based on polyethylene glycol (PEG; 1, 1.5, 2, 2.5, 3 and 4%) and NaCl (0, 50, 100 and 150 mM), on growth characteristics, physiological parameters and antioxidant defense system of sweet violet under in-vitro conditions. The influences of NaCl and PEG gradients in the culture media on plant height, green leaf percentage, root dry weight (DW), and electrolyte leakage (EL) was described by a linear or quadratic model. All measured parameters (except EL) decreased when NaCl or PEG concentration increased. In contrast, EL increased other traits. Moreover, with increasing in salinity and drought severity, shoot DW decreased, while antioxidant enzymes activity such as catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) and proline content increased. However, total soluble carbohydrates (TSC), at all drought levels, increased with increasing NaCl concentration up to 50 or 100 mM, and then decreased. Most variations in the shoot DW, CAT activity, proline and TSC contents due to salt stress occurred at low concentration of PEG. Overall, our findings highlight that the effect of combined drought and salt stress was more severe. However, the sensitivity of the plant to drought or salinity stress was higher in the absence of other stress.