Volume 14, Issue 3 (10-2023)                   2023, 14(3): 73-85 | Back to browse issues page


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Department of Soil Science and Engineering, College of Agriculture, Razi University, Kermanshah, Iran.
Abstract:   (722 Views)
Abstract
The use of plant hormones has been introduced as a simple and suitable strategy to reduce the adverse effect of heavy metals in plants. To investigate the effect of salicylic acid (SA) in reducing lead (Pb) stress in tomato (Lycopersicon esculentum L.), a factorial experiment was conducted based on completely randomized design with three replications in the greenhouse of Razi University. Factors included soil Pb contamination at three levels (0, 150 and 300 mg kg-1 soil as Pb(NO3)2) and SA at three levels (0, 250 and 500 μM). Results showed that the highest proline content (23.4 mmol g-1) and Pb concentration (4.26 mg kg-1) were obtained in 300 mg kg-1 of Pb and 0 μM SA, which shows an increase of 303 and 387%, respectively, compared to the control (without Pb and SA). Also, the highest amount of soluble sugars (0.48 mg kg-1), plant height (43.5 cm), root length (18.3 cm/plant), shoot dry weight (7.48 g/plant), and leaf area (263.1 cm2/plant) were found in the treatment of 500 μM SA and 0 mg kg-1 Pb. In general, the results showed that the application of SA, as a plant hormone, is a simple and convenient method to reduce the adverse effects of Pb stress in tomato.

Background and Objective: Heavy metals are non-biodegradable and persistent in nature thereby disrupting the environment and causing huge health threats to humans (Ferronato and Torretta, 2019). Lead (Pb) is a toxic heavy metal that enters the environment through various anthropogenic sources, and inhibits plant growth and development. Lead toxicity may result from disturbance in plant metabolism as a consequence of disturbance in the uptake and translocation of mineral nutrients (Hussain et al., 2017). A new method for reducing the effect of heavy metals on plants is the use of growth regulators such as salicylic acid (SA) (Vaculík et al., 2019). Tomato (Lycopersicon esculentum) is an important vegetable that is rich in minerals, various vitamins and antioxidant compounds. Since the cultivation of tomato, as an important and highly productive crop, is very common in many parts of Iran, including on the side of the roads, there is a possibility of contamination of the arable soils with lead. Therefore, the present study was conducted to evaluate the effects of foliar spraying of salicylic acid on reducing Pb-induced stress in tomato (Lycopersicon esculentum L.).

Methods: A factorial experiment based on a completely randomized design with three replications was conducted in the greenhouse of Razi University. Factors included Pb at three levels (0, 150 and 300 mg kg-1 as Pb(NO3)2) and SA at three levels (0, 250, and 500 μM). The solutions containing Pb(NO3)2 were sprayed uniformly on the soil sub-samples according to the desired concentrations. The samples were kept moist for 30 days close to the soil field capacity (FC). At the four-leaf stage, SA foliar spraying started and replicated three times until the beginning of flowering. After harvest, some characteristics including soluble sugars and proline content, plant height, shoot and root dry weights, and root volume and length were determined. Also, Pb concentration in leaf extract were measured by Varian AA220 atomic absorption spectrophotometer. The analysis of variance (ANOVA) and mean comparisons (Duncan's multiple range test, p < 0.05) were performed using SPSS-16 software.

Results: The results revealed that Pb stress reduced all plant characteristics, such as plant height, root volume and root length, as well as, dry weights of shoot and root, and elevated leaf Pb concentration, proline content and soluble sugars in tomato. However, the SA application resulted in improvement of growth traits. Also, the results showed that the interaction effect of Pb and SA on the most growth characteristics such as plant length, shoot and root dry weights, leaf area, and proline content, soluble sugars and Pb concentration was significant. The highest proline content (23.4 mmol g-1) and Pb concentration (4.26 mg kg-1) were obtained in 300 mg kg-1 of Pb and 0 μM SA. Also, the highest amount of soluble sugars (0.48 mg kg-1), plant height (43.5 cm), root length (18.3 cm/plant), shoot dry weight (7.48 g/plant), and leaf area (263.1 cm2/plant) were found in the treatment of 500 μM SA and 0 mg kg-1 Pb. It seems that under Pb-induced stress, applying SA, as a plant hormone, is an effective approach for improving crop growth by increasing plant resistance.

Conclusions: The results showed the significant negative effect of lead (Pb) on all the measured growth characteristics, including plant height, shoot dry weight, leaf area, root length, surface, volume and dry weight of tomato, as well as the amounts of proline and soluble sugars. The salicylic acid (SA) improved the resistance of tomato plants to Pb stress by increasing plant growth indices. In general, the application of appropriate concentration of SA (i.e., 500 μM) is an economic and easy strategy to reduce the effects of Pb (300 mg kg-1 soil) in tomato.

References:
1. Ferronato, N., Torretta, V., 2019. Waste mismanagement in developing countries: a review of global issues. Int. J. Environ. Res. Public Health. 16(6), 1060. https://doi.org/10.3390/ijerph16061060.
2. Hussain, I., Siddique, A., Ashraf, M., Rasheed, R., Ibrahim, M., Iqbal, M., Akbar, S., Imran, M. 2017. Does exogenous application of ascorbic acid modulate growth, photosynthetic pigments and oxidative defense in okra (Abelmos chusesculentus L.) under lead stress? Acta Physiol. Plant. 39, 144151. https://doi.org/10.1007/s11738-017-2439-0
3. Vaculík, M., Lux, A., Luxová, M., Tanimoto, E., Lichtscheidl, I., 2019. Silicon mitigates cadmium inhibitory effects in young maize plants. Environ. Exp. Bot. 67(1), 5258. https://doi.org/10.1016/j.envexpbot.2009.06.012 
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Type of Study: Research | Subject: Plant growth under stressful conditions
Received: 2023/07/27 | Accepted: 2023/09/20 | Published: 2023/12/19

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