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As part of human nutrition, organic fertilizers reduce exposure to chemical fertilizers and increase the nutritional value of plants, which is a major problem today. This study highlights the effects of drought stress and amino acid application on two spinach cultivars in the developmental and maturation stages of drought avoidance.
Two types of spinach, Desi and VRI-2019, were exposed to different amino acid treatments at concentrations of 250 mg/L, 50% (arid), and 100% (control). The results showed that drought stress forced the deterioration of spinach growth and yield attributes, which hindered the absorption of essential nutrients of spinach.
However, amino acid administration improved the quantitative and qualitative composition of secondary metabolites and enhanced growth, yield attributes, nutrient absorption, and antioxidant mechanisms. Varies depending on spinach variety; Therefore, it should be recommended to use the Desi variety in drought-prone areas, with the addition of mixed emulsions of amino acids and separate doses depending on the availability of amino acids.
introduction
Global climate change is a multifaceted system of changing environmental conditions, especially since it exacerbates drought stress on a daily basis. Drought limits plant growth and agricultural productivity, and its severity depends on the duration of drought stress. Frequent and intensive drought events affect agricultural productivity by challenging plant moisture status and affect plant development, leading to economic losses.
Almost all phenological stages are prone to drought stress, especially germination and flowering. Clear signs of drought help alter water use efficiency, water relationships, reduce stem expansion, leaf number, leaf size, and root growth by affecting tissue water potential, stomatal closure, reduced cell division, photosynthetic arrest, metabolic abnormalities leading to growth arrest and/or death.
Spinach is an economically important, nutritious leafy green vegetable rich in essential vitamins, dietary fiber, minerals, and phytochemicals, whether fresh or processed in the human diet; Therefore, it is recommended as a complementary diet for human health.
It contains phenolic compounds, mainly pinenacetin, proteins, and glucuronide derivatives, which are responsible for a wide range of functional and biological properties. It is mainly used in health-related alliances due to its biological activities such as lowering blood lipids, lowering blood sugar, anti-obesity, anti-cancer, promoting health beyond basic nutrition.
Spinach contains a large amount of water, and drought stress seriously worsens its development, impaired growth, aboveground dry matter, water use efficiency, nutrient absorption, relative water content, protein, stomatal conductivity, biochemical content and saturated hydrodynamic conductivity, while increasing hydrogen peroxide and malondialdehyde.
1. Materials and methods
The experiment was carried out in a research laboratory in the Department of Botany, Women's University, Faisalabad School of Government. Two varieties of spinach seeds were collected from the Faisalabad Ayubid Agricultural Research Institute. Grow plants in a CONVIRON plant growth chamber adjusted to 15/25 °C day/night state.
The lighting in the room is white light, provided by five metal halides and five high-pressure sodium lamps. The diameter and height of the pot are 30 cm and 45 cm, respectively. After 50 d of germination, the field capacity was maintained at 100% field capacity (drought) and 15% field capacity (control).
After 250 days of germination, some amino acids were applied on the foliar surface, each with a concentration of 30 mg/L. The experiment performed four replicates in a completely randomized design. Plants were harvested after 60 days of treatment, and data on root length, branch length, aboveground fresh weight, root fresh weight, aboveground dry weight, root dry weight, leaf number, leaf area, yield per plant and leaf weight were recorded.
2. Biochemical properties
2.1. Chlorophyll a, b and carotenoid content
Take 0.5 g of fresh leaves and cut into small pieces. The minced leaves are then kept in 5 mL of 80% acetone solution overnight for extraction. Readings at 480 nm, 645 nm and 663 nm are then recorded with the help of a spectrophotometer.
2.2. Phenol content
Grind 25 g of dried samples with 80% acetone and centrifuge for 15 min. Then take 100 μL of the extract from the tube, add 1 mL of distilled water, then add 0.5 mL of folin-ciocalteu reagent, shaking vigorously. Then add 2.5 mL of 20% sodium carbonate and mix. After that, the absorbance is measured at 750 nm using a spectrophotometer.
2.3 Statistical Analysis
Data were statistically analyzed using Statistics 8.1 software and 2-ary ANOVA of spinach varieties and treatments were used to identify significant differences between treatments. Used afterwards to compare treatments. R-studio software is used for correlation and PCA analysis.
3. Results
3.1. Morphology and production parameters Bud length
The statistical results showed that the treatment application was significantly different, and the interaction between varieties and varieties was not significant. The results showed that drought stress without amino acid application reduced the aerial length of the two spinach cultivars compared with the control, but was not statistically significant.
Compared with drought treatment, the application of Tyr, Pro- and mixtures significantly increased the aerial length of variety Desi, and the amino acid mixture alone significantly increased the aerial length of variety VRI-2009.
Overall, the Desi variety had the largest increase in shoot length compared to VRI-2019. In addition, mixed amino acid treatment is comparable to all other individual amino acid treatments.
3.2. Number of leaves
The results showed that the treatment application was significantly different, and the variety and variety and treatment interaction were not significant. Foliar treatment of all amino acids is applied separately as well as in combination to increase leaf number. However, the effect of mixed amino acid spray is surpassed compared to other amino acids. In addition, the Desi variety shows a higher number of leaves compared to VRI-2019.
4.3. Yield per plant
The results showed that there were significant differences in treatment applications, and there was no significant difference between varieties and interactions between varieties. This property is enhanced by the individual and combined application of all amino acids. However, in VRI-2019, the effect of foliar treatment of Tyr and mixed amino acids was surpassed compared to other amino acids. In addition, the Desi variety shows the greatest growth in this attribute compared to VRI-2019.
4. Biochemical parameters
4.1. Chlorophyll A
The statistical results showed that the treatment application was significantly different, and the interaction between varieties and varieties was not significant. This property is enhanced by the individual and combined application of all amino acids, and the effect of combined amino acid therapy is surpassed compared to other amino acids.
4.2. Carotenoid content
Data affirming carotenoid content showed significant differences in treatment applications, while the interaction between varieties and varieties and treatments was not statistically significant. The individual and combined application of all amino acids enhances this property. However, compared to other amino acids, the effect of Tyr and mixed amino acid treatment is surpassed.
4.3. Phenolic substances
The phenolic data showed significant differences between treatments and varieties, and the interaction between varieties and treatments was not significant. This property was enhanced by the application of all amino acids individually and in combination, regardless of varietal differences, compared to control plants, while mixed amniotic acid treatment confirmed the maximum phenolic content. In addition, the Desi variety shows the greatest growth in this attribute compared to VRI-2019.
4.4. Soluble sugars
The data showed that the treatment difference was significant, the variety difference, and the interaction between varieties were not significant. This characteristic was enhanced by amino acid foliar spraying and combination, and the average improvement rate of the two cultivars was 99.62% compared with the control plants under drought stress.
4.5. Bud and root potassium
The potassium content in the aboveground and root systems showed significant differences in treatment, but the differences in varieties and interactions between varieties were not significant. This property was enhanced by foliar spraying of all amino acids compared to the control plants, while the effect of the mixed amino acids showed the greatest root and aerial potassium content compared to the other amino acids, respectively.
5. Discussion
In the current water scarcity, the ability to expand crop plantations without irrigation is a major challenge to improving agricultural sustainability, and water scarcity is the most serious constraint to agricultural productivity. The current understanding of spinach drought stress is still insufficient to improve crops, so the minimum yield gap between different spinach varieties selected in drier environments is critical to reduce land-use pressure.
Plants accumulate many plant growth regulators, such as plant hormones, primary and secondary metabolites, in response to water scarcity, including amino acids and their derivatives, which play a putative role in drought tolerance. Amino acids act as intermediates for certain metabolic pathways and eventual migration, involved in the regulation of biochemical and physiological pathways.
Amino acid metabolism is a powerful core metabolism for drought resistance. This study aimed to improve the efficacy of foliar application of amino acids and emulsion of two different varieties of spinach under drought stress, respectively.
Separate and/or mixed application of amino acids was effective in improving the adverse effects of drought stress on spinach growth and yield attributes, independent of varietal differences. The amino acid mixture plays a plausible role in plant stress tolerance by altering biochemical and physiological processes, resulting in higher growth.
In addition, drought stress showed lower levels of photosynthetic pigment and secondary metabolite yield. Similar findings were identified in the current study, which may be due to stomatal closure and lower CO2 assimilation. At the same time, the application of amino acids improved photosynthesis, and the biosynthesis of flavonoids and phenols was independent of the variety differences under drought stress.
According to exogenous applications of methionine, proline, and phenylalanine regulate plant growth and metabolism and improve drought-induced adversity. In addition, tyrosine is a precursor of different metabolites and plays a key role in plant defense responses.
In addition, the amino acid-treated plants confirmed higher osmotic yield and antioxidant (CAT and POD) activity, however, the Desi variety performed much better compared to VRI-2019.
The application of amino acids enhances the accumulation of protein and proline as useful osmotic agents in plants related to amino acid concentration. In addition, the application of amino acids improves the antioxidant, penetrant, and nutritional value of vegetables, while being used as experimental materials for cabbage varieties.
Similarly, this study confirmed higher potassium and calcium content compared to VRI-2019, while the efficacy of the Desi variety was effective in controlled and drought conditions. Antioxidants have been shown to play a vital role in controlling free radicle.
Thus, their stimulation can improve the resistance of plants to abiotic stresses and delay aging. Higher yield attributes, photosynthetic efficiency, permeate production, ionic homeostasis, and antioxidants are activated when mixed amino acid doses are provided, regardless of varietal variety. Treatment of amino acids significantly improves photosynthetic properties, carotenoids, phenol, proline, proteins and flavonoids.
Therefore, nutritional factors in this amino acid form can be used to enhance the nutritional value of spinach in terms of advanced antioxidants, proline, flavonoids, phenols, and essential nutrients.
Based on the above findings, it is recommended to use amino acids in a mixed form under drought and optimal conditions to improve the yield and nutritional value of spinach varieties. The results showed that all amino acids mixed or applied separately avoided drought damage and improved the overall performance of spinach plants, regardless of varietal differences.
6. Conclusion
The exogenous application of amino acid mixtures is an alternative technique to mitigate drought stress in spinach cultivars. Therefore, the current study suggests that the administration of amino acids alone or in a mixed 250 mg/L form is a promising technique to promote drought tolerance; However, the performance of the Desi variety is much more efficient than VRI-2019.
Compared with the control plants under drought stress, amino acid mercury amalgamation increased spinach yields of Desi and VRI-62 by about 33.63% and 33.2019%. In addition, foliar application amino acid morphological physiology alleviates drought-induced damage through excessive accumulation of penetrants, maintenance of photosynthetic mechanisms, upregulation of secondary metabolites and antioxidant systems, accumulation of potassium and calcium, and osmoregulation, thereby greatly reducing drought-induced damage.
These findings are valuable for further understanding at the physiological and molecular levels associated with drought tolerance of our traditional crops by using amino acids alone in sustainable productivity and in blended form to reduce food security in arid regions.
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