Document Type : Original Article

Authors

• Raheleh Rahbarian ¹
• Elham Azizi ²
• Asieh Behdad ³
• Atena Mirblook ⁴

¹ Department of Biology, Faculty of Science, Payame Noor University, Tehran, Iran

² Department of Agricultural Sciences, Payame Noor University, Tehran, Iran

³ Postdoc of Plant Physiology, Department of Biology, Faculty of Science, Ferdowsi University of Mashhad, Iran

⁴ PhD in Soil Science and Plant Nutrition, Soil Science Department, Urmia University, Iran

Abstract

Introduction
Dracocephalum moldavica L. is a herbaceous, annual plant from the Lamiaceae family that is native to Central Asia and domesticated in Central and Eastern Europe. Essential oil of this plant has antimicrobial and bacterial properties and has many uses in the pharmaceutical, cosmetic, food and perfumery industries. Lead stress in plants causes disturbances in mitosis, leaf chlorosis, decreasing of the vegetative and productive growth stages and reduces photosynthesis and enzyme activities. One of the effects of lead toxicity is due to the similarity of the structure of calcium ions and lead, and for this reason, lead ions disrupt many mechanisms related to calcium ions and prevent the activity of key enzymes.Photosynthesis is one of the most sensitive metabolic processes to lead toxicity, and several studies have reported the inhibition of photosynthesis under lead stress in various plants. Lead prevents the absorption of elements such as magnesium and iron. These elements play a role in the structure of chlorophyll and the oxygen-releasing complex in photosystem II. Heavy metals such as lead inhibit chlorophyll biosynthesis by inhibiting the enzymes gamma-aminolevalonic acid dehydrogenase and protochlorophyll reductase. Also the availability of different nutrients in the soil changes significantly under the influence of environmental stress so that using of vermicompost can be useful in stress condition as well as Jasmonate. Jasmonate is the final oxidation product of unsaturated fatty acids such as linolenic acid, that is effective in increasing the activity of plant defense systems under environmental stress conditions such as lead stress. In order to study the effect of pb (0, 100, 200, 300, 400 mg kg^-1 soil) and jasmonate (0, 50, 100, 150 mmol l^-1) on Dracocephalum moldavica L. under controlled conditions in soil enriched with vermicompost and without vermicompost an experiment designed and it was done under greenhouse conditions.
Materials and methods
This test was done in a random factorial design with 4 repeats and indices including CO₂ assimilation rate, transpiration rate, stomatal conductance, water use efficiency(WUE), PSɪɪ photochemical efficiency (Fv/Fm), photosynthesis quantum performance, electron transfer rate (ETR), were measured in vegetative and reproductive growth stages.
Results and discussion
In the conducted study, it was found that CO₂ assimilation rate, water use efficienty, stomatal conductance and Fv/Fm were significantly decreased as lead concentration was increased. Also jasmonate treatment significantly increased CO₂ assimilation rate, water use efficienty, stomatal conductance and Fv/Fm in lead stress condition. So that plant treated with 400 mg kg^-1 soil pb and 0 mmol l^-1 jasmonate showed the lowest CO₂ assimilation rate, water use efficienty, stomatal conductance and Fv/Fm while plant treated with 0 mg kg^-1 soil pb and 150 mmol l^-1 jasmonate showed the highest CO₂ assimilation rate, water use efficienty, stomatal conductance and Fv/Fm. transpiration rate was significantly increased as well as increasing pb concentration so that plant treated with 400 mg kg^-1 soil pb showed the highest transpiration rate. Also jasmonate treatment significantly decreased transpiration rate in lead stress condition. Vermicompost increased CO₂ assimilation rate, water use efficienty, electron transfer rate (ETR) and significantly decreased transpiration rate in lead stress condition.
Jasmonate reduces the destructive effects caused by stress on photosynthetic indicators such as the amount of chlorophyll and carotenoids and also increases the performance of photosystem II and consequently increases plant photosynthesis under stress conditions. It has been reported that methyl jasmonate can maintain the concentration of chlorophyll in the reaction center, thereby improving the speed of electron transfer and increasing the efficiency of photosystem II. In addition, jasmonate can prevent the severe reduction of stomatal conductance under stress conditions and increase the quantum efficiency of photosynthesis.
In the response of plants to stress, jasmonates act as genes encoding inhibitory proteins such as theonine, hydroxyproline and proline, and in general, by activating defense mechanisms, they help the plant in reducing the absorption and accumulation of heavy metals. Organic fertilizers can also improve plant performance under environmental stress conditions. Vermicompost fertilizer increases porosity, increases absorption and retention of nutrients, improves ventilation, drainage and microbial activity in the soil.
Conclusion
Having nutritious mineral elements and plant growth hormones can improve plant growth in the presence of environmental pollutants such as heavy metals by influencing the physiological characteristics. It can be said based on the results obtained lead stress decreased photosynthesis index through effect on electron transport chain and photosynthetic pigments while jasmonate treatment and Soil enriched with vermicompost can reduce the destructive effects of lead stress. So that using of jasmonate and vermicompost in lead stress condition Recommended.
 

Keywords

• CO2 assimilation rate
• Dracocephalum moldavica L
• Fertilizer
• Fv/Fm
• Heavy metal stress

Main Subjects

• Heavy metals