The effect of salicylic acid on some morphological characteristics, photosynthetic pigments and antioxidant system activity of basil (Ocimum basilicum L.) under arsenic toxicity

Basil (Ocimum basilicum), a member of Lamiaceae family, is used in traditional Iranian medicine. Essential oils of basil leaves are composed of phenylpropanoids which are important in treatment of headaches, diarrhea, coughs, warts, worms and kidney malfunctions. The most important phenylpropanoid compounds contain eugenol, chavicol, methyl eugenol, methyl chavicol, myristicin, methyl cinnamat and elemicin. Heavy metals pollution is a major problem of crops and medicinal plants production inthe large parts of the world which has a negative impact on all aspects of plant growth and production. Heavy metal toxicity is one of the major current environmental health problems and potential dangerous due to bioaccumulation through the food chain and in plant products for human consumption. Arsenic is a heavy metal with high toxicity that absorbed by plants mainly through the root system and in minor amounts through the leaves. After entering the cells, lead inhibits activities of many enzymes, and affects membrane structure and permeability. Today, phenolic compounds and plant growth regulator has been proposed, to reduce the negative effects of stress. Salicylic acid is a substance that causes plant resistance to biotic and abiotic stresses. Salicylic aside inhibit the production of reactive oxygen species and protect plants against ROS damages. This study was to evaluate the effect of Salicylic aside spray on some morphological characteristics, photosynthetic pigments activities of antioxidant enzymes basil was conducted under arsenic stress.

This study was conducted at the Faculty of Agriculture, University of Zabol a factorial in a completely randomized design with three replications. The experimental treatments was included arsenic stress 0 (control), 10, 45 and 80 mg per kg of soil and application of salicylic acid at 3 levels of 0, 1 and 2 mM. T. Physiological traits (Chlorophyll a, b and T. chlorophyll, Carbohydrate, Carotenoid), morphological characteristics (fresh and dry weight, leaf area) and activities of antioxidant enzymes (Peroxidase and Catalase) were estimated in this experiment. The statistical analyses were carried out using the SAS version 9. The treatment means separated using Duncan's multiple-range test (DMRT) taking P < 0.05 as significant.

Based on the results, increasing of stress severity reduced some traits, So that addition of 80 mg per kg of soil arsenic significantly reduced amount of fresh and dry weight, leaf area , chloroohyll a, b and total, carotenoid and increased concentrations of carbohydrate and anti-oxidant enzyme (catalase and peroxidase ). Also, the results of simple effects of foliar application levels showed that by increasing the concentration of foliar application, the traits were increased, so that The highest fresh and dry weight, leaf area , chloroohyll a, b and total, carotenoid and carbohydrate was obtained in plants spraying with 2 mM SA, But reduced the activity of the antioxidant compounds. on the other hand, In this study the interaction between salicylic acid and arsenic on chloroohyll a, b, total and anti-oxidant enzyme catalase and peroxidase were significant, so that the highest of amount of chloroohyll a, b and total, were obtained in plants subtended in sprayed with 2 mM SA and without stress, But the highest the activity of the antioxidant enzyme catalase and peroxidase were obtained in plants Under in stress 80 mg per kg of soil arsenic and without sprayed.

Our observations indicated that ascorbic acid spraying at lower concentration might be favorable to improve growth and defense ability against arsenic toxicity in basil though field testing would be required to verify this and Based on the findings of this study, as well as supplemental studies, salicylic acid spraying can be proposed to improve the growth and reduce the arsenic toxicity of Basil plant under arsenic stress.