The response of quantitative and qualitative characteristics of Isabgol (Plantago ovata Forssk.) to foliar application of salicylic acid and spermine under drought stress conditions

Introduction Drought stress is considered as one of the most important environmental problems in agriculture and the growth of plants. The persistent shortage of water causes early aging of the leaves of plants. During this process, the chloroplasts are destroyed and photosynthesis activity sharply reduced. The adaptation of plants to drought stress is the result of a change in many morphological and biochemical mechanisms which lead to changes in plant growth rate, stomatal conductivity, photosynthesis process speed, and enzyme activity. The ability of plants to compromise in environmental stresses depends on the type, intensity and duration of stress and plant species. Salicylic acid is a phenolic compound known as an important molecular signal in plant fluctuations in response to environmental. Also alters a number of metabolic pathways including synthesis, oxidation and some biological activities including respiration, photosynthesis and absorption. Polyamines (PA) are a group of phytohormone-like aliphatic amine natural compounds with aliphatic nitrogen structure which are present in whole living organisms including plants. They play a role in collecting active radicals and increasing the tolerance of plants to abiotic stresses including salinity, drought and senescence. Plantago ovata Forssk is an annual herbal plant belonging to the Plantaginaceae family. So, among 28 species from Plantago genus, this species aspect economical is commercial source of mucilage. In recent years, according to reorganization plan for cultivation of medicinal plants in country, this crop has been recommended aspect 10 priority species of medicinal plants. Therefore, the purpose of this study was to evaluate the effect of foliar application of salicylic acid and spermine on some quantitative and qualitative characteristics of isabgol in water deficit conditions. Materials and methods The study was conducted as a split plot factorial experiment based on a randomized complete block design with 18 treatments and three replications in research field of the Gonbad Kavous University, Golestan Province, Iran in 2016. In this experiment, the treatment of irrigation included (non-stress: control), irrigation cutoff at flowering stage and irrigation cutoff at seed filling stage was the main-plot and factorial of salicylic acid (zero, 0.4 and 0.8 mM), plus spermine spraying (zero and 0.02 mM) were as a sub-plot. Foliar application of salicylic acid and spermine at budding (inflorescence production), flowering and seed filling stages were applied. Results and discussion Analysis of variance of data showed that in most of the characteristics, the combined effects of irrigation cutoff, salicylic acid and spermine, were significant at 1 or 5 percentage confidence levels. According to the results of the maximum grain and biological yield were found in the combined treatments of 0.8 mM salicylic acid spraying at irrigation interruptions at grain filling stage about 540.8 kg/ha-1 and 2795 kg/ha-1 respectively. The maximum amount of grain mucilage (19.7%) and swelling rate per gram mucilage (105.7 mg.l-1) were obtained in the treatment of 0.4 mM salicylic acid and 0.02 mM spermine in the absence of tension. According to the results, the foliar application of salicylic acid and spermine in cutoff irrigation conditions at flowering and seed filling stages significantly loss prevented more studied characteristics. It is concluded that the effective role of salicylic acid and spermine in osmotic regulation, membrane stability and elimination of active cell radicals could increase the tolerance of isabgol herb in water stress conditions. Conclusion According to the findings of this experiment and the research done on other plants, it was concluded that the‌ leaf foliar application of medicinal plants with phenolic and polyamines compounds such as salicylic acid and spermine with suitable concentrations can be considered as an effective step to reduce the adverse effects of water stress and finally increase the qualitative and quantitative characteristics of plant.