Changes in morpho-physiological characteristics and the leaf and flower essential oils yeild of coneflower [Echinacea purpurea (L.) Moench] with sodium nitroprusside (SNP) foliar application under drought stress

Drought stress (water scarcity) is one of the most limiting environmental factors in plant growth and production. Sodium nitroprusside (SNP) as a nitric oxide doner compound (NO) plays an important role in reducing the oxidative stress caused by abiotic stresses. In order to investigate the effect of SNP foliar application on some biochemical characteristics, growth and yield of Echinacea purpurea Moench L. under drought conditions, an experiment was conducted in a split plot design in a completely randomized block design with three replications at the Research Institute of Agriculture, Institute of Forest and Rangelands, Karaj, Iran, in 2015-2016. The experimental treatments included SNP factor at four levels (0, 100, 200 and 400 µM) and drought stress factor at three levels [30% field capacity (severe), 60% field capacity (moderate), 90% field capacity (control)]. At full flowering stage, plant height, number of lateral branches, leaf and flower number, dry weight of shoots and percentage and yield of shoot essential oil were measured. Also, leaves sampling was performed to measure relative water content (RWC), chlorophyll content, the activity of superoxide dismutase (SOD) and peroxidase (POD) enzymes, malondialdehyde (MDA), total phenol and proline contents. Results showed that the hieghest amount of morphological triats and shoot dry weight were related to 200 µM SNP concentration under non drought stress (control) condition. The highest amount of RWC was obtained (97.9%) in 90% moisture treatment (control) and 200 µM of SNP. Also, higher concentrations of SNP (200 and 400 µM) under moderate stress (60% of crop capacity), could increase the plant drought stress tolerance by increasing the SOD and POD enzymes activity as well as reducing MDA content. The highest amount of proline (16.7 µmol/g fr wt) and total phenol (127.7 mg GAE/g dry matter) were also related to 400 µM SNP treatment. In general, SNP foliar application especially at 200 µM concentration under drought stress conditions could modify drought stress damage, and increase active ingredient of the plant.