Document Type : Research Article
Authors
1
Department of Horticulture, Faculty of Agriculture, Lorestan University, Lorestan, Khorramabad, IRAN.
2
Department of Horticulture, Faculty of Agriculture, Lorestan University, Khorramabad, Lorestan, IRAN
3
Department of Plant Protection, Faculty of Agriculture, Lorestan University, Khorramabad, Lorestan, IRAN.
Abstract
Introduction
Climate change is causing soil salinization, resulting in crop losses throughout the world. Among plant responses to salinity, mechanisms that control ion uptake, transport, and balance—as well as water potential, photosynthesis, cell division, osmotic adjustment, enzymatic activities, polyamine regulation, stress signaling, and formation of root apoplastic barriers— play critical roles in salinity tolerance. To enhance plant tolerance to salinity stress, elicitors are employed as a short-term and viable solution to mitigate the adverse effects of stress. Pseudomonas putida, Curtobacterium spp., and L-glutamic acid play a vital role in maintaining normal plant growth and metabolism by influencing photosynthesis and respiration processes. These beneficial microorganisms and compounds serve as cofactors for enzymes such as catalase and ascorbate peroxidase, actively contributing to the removal of reactive oxygen species (ROS). Chrysanthemum morifolium is globally recognized as one of the most important ornamental plants, valued for both its medicinal and edible uses. Its remarkable diversity in flower types, colors, and plant architecture has secured its prominent position in the floriculture industry. Known as the "Queen of the East," this cut flower belongs to the Asteraceae family. Given the ornamental and medicinal importance of chrysanthemum and the prevalence of salinity stress, this study aims to explore the impact of Pseudomonas putida, Curtobacterium spp., and L-glutamic acid spray. Specifically, it investigates how these treatments the effects of salinity stress on the morphophysiological and biochemical characteristics of chrysanthemum."
Materials and Methods
A factorial experiment was conducted using a completely randomized design with three replications in the research greenhouses of Lorestan University's Faculty of Agriculture. The experimental conditions included daytime temperatures ranging from 20 to 28 °C, nighttime temperatures from 15 to 20 °C, relative humidity maintained at 60-70%, and a light intensity of 400-500 µmol·m⁻²·s⁻¹. The first factor involved salinity levels at concentrations of 0 (control), 30, 60, and 90 mg·L⁻¹, while the second factor included five levels: control, L-glutamic acid at 300 and 600 mg·L⁻¹, and growth-promoting bacteria (Pseudomonas putida and Curtobacterium spp). four-leaf seedlings were obtained from standard greenhouse in Pakdasht and planted in 1.5-liter pots, with each pot containing one plant. The growth-promoting bacteria were applied twice: first by root immersion at planting, and then by foliar spraying eight days after planting. L-glutamic acid was applied three times: the first application occurred two weeks after planting, followed by two additional applications at 20-day intervals. All treatments were administered through irrigation every three days at a level corresponding to 90% of the field capacity. The soil mixture comprised an equal ratio of agricultural soil, sheep manure, and sand, maintaining a clay-sand loam texture. Following 128 days of applying salt stress and 45 irrigations, a comprehensive assessment of morphophysiological characteristics was carried out. This included the measurement of plant height, stem diameter and length, leaf area, fresh and dry weights of stem, root, leaf and cluster, root volume, diameter and length, root/shoot ratio, stress tolerance index, relative water content (RWC), electrolyte leakage, malondialdehyde content, photosynthetic pigments, as well as the activity of peroxidase and ascorbate peroxidase.
Results and Discussion
The results indicated that salinity stress had a detrimental impact on various aspects of plant growth, including a decrease in plant height, stem diameter and length, leaf area, fresh and dry weights of stem, root leaf and cluster, root volume, diameter and length, root/shoot ratio, stress tolerance index, relative water content (RWC), electrolyte leakage, malondialdehyde content, photosynthetic pigments. Additionally, salinity stress led to increased levels of electrolyte leakage, malondialdehyde content, and enhanced activity of antioxidant enzymes, namely catalase and ascorbate peroxidase, highlighting its adverse effects on plant development. The decline in plant growth under salinity stress can be attributed to several physiological disruptions, including diminished cell division, ionic imbalance, reduced water uptake, impaired absorption of essential nutrients, and the toxic effects of ions—particularly sodium and chloride. Other contributing factors include impaired absorption and metabolism of nitrogen and protein, as well as stomatal closure, all of which collectively reduce photosynthetic efficiency. Salinity stress also decreases soil water potential and increases the osmotic pressure of the soil solution. As a result, the plant must expend more energy to absorb water, leading to elevated respiration rates and hormonal imbalances in plant tissues. These physiological disruptions ultimately result in reduced growth and overall negative impacts on plant health. The results demonstrated that the application of both categories of growth promoters not only exerted positive effects on plant growth indices, but also significantly reduced oxidative stress—as evidenced by decreased electrolyte leakage and malondialdehyde content—while enhancing the activity of the plant's antioxidant enzyme system. Notably, L-glutamic acid acted as an effective physiological regulator at differential concentrations (600 and 300 mg·L⁻¹ under moderate and severe stress conditions, respectively). Pseudomonas putida, Curtobacterium spp., and L-glutamic acid collectively improved plant performance under salinity stress by modulating cellular antioxidant levels and hormonal balance within plant tissues.
Conclusions
The findings of this study indicated that increased salinity stress led to higher electrolyte leakage and malondialdehyde content, along with a reduction in RWC and photosynthetic pigments. These changes caused a decline in the morpho-physiological characteristics of chrysanthemum. However, salinity stress also increased the activity of catalase and ascorbate peroxidase enzymes. Foliar application of Pseudomonas putida, Curtobacterium spp ., and L-glutamic acid under these conditions had beneficial effects on the plants. Notably, L-glutamic acid demonstrated significant ameliorative effects at concentrations of 600 mg·L⁻¹ under moderate stress and 300 mg·L⁻¹ under severe stress. These improvements were associated with increased antioxidant enzyme activity, higher RWC, and elevated levels of photosynthetic pigments.
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