Daniel K. Struve

Effect of SiO2 nanoparticles on drought resistance in hawthorn seedlings

Abstract Drought is a significant factor limiting crop production in arid regions while hawthorns (Crataegus sp.) are an important component of such region’s forests. Therefore, treatments that increase hawthorn drought resistance may also increase transplanting success. Thus, the physiological and biochemical responses of hawthorn seedlings to a factorial combination of different concentrations of silica nanoparticles (SNPs at 0, 10, 50 and 100 mg L−1) and three soil moisture treatments (without stress, moderate stress and severe stress) were investigated. Seedlings were irrigated with one of the four concentrations of SNPs for 45 days before exposing them to drought stress. Photosynthesis parameters, malondialdehyde (MDA), relative water content (RWC), membrane electrolyte leakage (ELI) as well as chlorophyll, carotenoid, carbohydrate and proline content were determined. At the end of the experiment, positive effects by SNP pre-treatment on physiological indexes were observed during drought stress. Under drought conditions, the effect of SNPs on photosynthetic rate and stomatal conductance was evident. Although the SNPs increased plant biomass, xylem water potential and MDA content, especially under drought conditions, RWC and ELI were not affected by the SNP pre-treatments. Seedlings pre-treated with SNPs had a decreased carbohydrate and proline content under all water regimes, but especially so under drought. Total chlorophyll content and carotenoid content did not change among the treatments. Generally, the findings imply that SNPs play a positive role in maintaining critical physiological and biochemical functions in hawthorn seedlings under drought stress conditions. However, more studies are needed before the physiological and biochemical basis of induced drought resistance can be determined.

Change in biochemical parameters of Persian oak (Quercus brantii Lindl.) seedlings inoculated by pathogens of charcoal disease under water deficit conditions

Key messageDrought alone or in combination with charcoal disease pathogens led to modifications in some biochemical characteristics of Persian oak seedlings. Drought conditions enhances the effects of charcoal fungus with effects at biochemical level.AbstractCharcoal disease is one of the common diseases in oak forest of Zagros in western Iran that has increased in the recent years. The disease is associated with abiotic stress, especially drought, and contributes to the decline of Persian oak (Quercus brantii Lindl.), the major oak species in this forest association. Persian oak seedlings were exposed to a factorial combination of two irrigation levels and inoculation with either Biscogniauxia mediterranea or Obolarina persica (agents of charcoal disease). Proline, total soluble sugar and soluble protein contents in seedling foliage were increased in response to charcoal pathogen inoculation, especially when combined with water stress, while starch, chlorophyll a + b and carotenoid contents strongly declined. Pathogen inoculation stimulated malondialdehyde content, electrolyte leakage, and hydrogen peroxide and superoxide radical contents in oak leaves, and were increased by water stress. The combination of charcoal disease agents and water stress increased peroxidase and superoxide dismutase activity while, for catalase and ascorbate peroxidase activities, the interaction between the two factors of variability was not significantly increased. Ascorbate peroxidase activity was at maximum level in seedlings infected with O. persica independently of water stress. Glutathione reductase had the highest activity in inoculated seedlings under soil moisture stress while those under higher soil moisture levels, the enzyme was increased only when inoculated with O. persica. Contents of non-enzymatic antioxidants including ascorbic acid and glutathione increased in response to combined pathogen inoculation and water stress and was higher when seedlings were inoculated with O. persica than with B. mediterranea. Chitinase activity significantly increased because of pathogen inoculation. Furthermore, foliar phenylalanine ammonia lyase activity was higher under all treatment combinations, as compared to the controls. The effects of B. mediterranea or O. persica pathogens on foliar biochemical responses of Q. brantii seedlings were more severe under water-stress and it was more sensitive to B. mediterranea than O. persica.