Effect of different concentrations of paclobutrazol on alleviation of freezing stress effects in two populations of Kochia scoparia

Applications of chemical substances such as triazoles can alleviate the environmental stresses like cold stress. Therefore, a factorial experimental based on completely randomized design was conducted. Different concentrations of paclobutrazol (0, 10, 20 mg per liter) were applied on seedling roots environment before freezing stress and after that plants were exposed to freezing temperatures (0, -3, -6, -9, -12 and -16°C) under controlled conditions. Before applying freezing temperatures, soluble sugar, proline, total phenol, photosynthetic pigments and DPPH radical scavenging activity were measured. Following exposure to freezing temperatures, cell membrane stability and a temperature lethal to 50% of samples based on electrolyte leakage (LT50el) were determined. Survival and regrowth of plants were determined at three weeks after seedlings recovery under natural conditions. Results showed that the electrolyte leakage remained constant where the temperature was reduced to -9°C, and reducing the temperature to -12° C caused a sharp increase in electrolyte leakage. Moreover, plants survival was not influenced up to -9 ° C, but reducing the temperature to -12°C caused a significant reduction in plant survival. Paclobutrazol application increased chlorophyll a, b, DPPH radical scavenging activity and survival in kochia, whereas decreased proline, soluble carbohydrates, total phenol concentration and electrolyte leakage. Influence of Interaction between temperature and population on total pigments indicated an increase in pigment content in Broojerd population at 20 milligrams per liter of paclobutrazol, and proline and carbohydrates contents were significantly greater in Sabzevar population where no paclobutrazol was applied. Generally, application of 10 and 20 milligrams per liter of paclobutrazol prevented a severe reduction of kochia plants survival under freezing stress.