Abstract: Background and Objective: The L-tyrosine is one of the important natural amino acids used in promoting growth and productivity of various crops and used to build hormones. Salicylic acid (SA), is naturally produced compound with several promotive effects in plants. This study aimed to evaluate the physiological role of L-tyrosine and salicylic acid on growth, some biochemical aspects, yield and nutritional values of the peanut seeds under sandy soil conditions. Materials and Methods: During 2018 and 2019 summer seasons, 2 field trials were conducted at the Research and production Station of NRC, El-Nubaria Province, El-Beheira Governorate, Egypt. To study the physiological role of tyrosine and salicylic acid foliar treatment on vegetative growth (60 days after sowing, DAS), photosynthetic pigments in fresh leaves. Total carbohydrates, IAA (Indole acetic acid), flavonoids, β-carotene, lycopene, total phenol and enzyme activities (PAL and TAL) were determined in plant shoots. Moreover, yield and its components (Number of branches/plant, straw yield/plant, pod yield/plant, biological yield/plant, number of pods/plant, number of seeds/pod and seed yield/plant as well as seed quality (oil yield) and fatty acids of peanut grown under sandy soil conditions were recorded. Results: Results showed that, external treatment of L-tyrosine (50, 100 and 150 mg L–1) and salicylic acid (100, 200 and 300 mg L–1) increased significantly growth criteria and photosynthetic pigments, total carbohydrate, IAA and phenolic contents in shoots. In addition, yield and its components significantly increased with all treatments. The highest increases in seed yield (t ha–1) and oil yield (t ha–1) were recorded 14.45 and 144.93%, respectively when 100 mg L–1 tyrosine was applied. Moreover, all treatments caused significant increases in carbohydrate, oil, antioxidants compounds as flavonoids, β-carotene and lycopene contents, antioxidant activity and unsaturated fatty acids as compared with untreated control plants of the yielded peanut seeds. Conclusion: The L-tyrosine and salicylic acid has a regulatory role on growth, some biochemical aspects, yield quantity and quality as well as improve fatty acid composition of the yielded oil. The L-tyrosine with 100 mg L–1 was the best treatment on enhancing growth and productivity of peanut plant.
INTRODUCTION
Peanut (Arachis hypogaea L.) is cultivated in Egypt for fresh human consumption, oil production or export. Peanut seeds are rich with nutritional values i.e., protein, lipids, minerals as calcium and magnesium and vitamins1,2. Peanut seeds are used in different forms, such as soup thickener where they double as nutritional enhancers, snacks when cooked, roasted, dried or fried. Recently, a peanut sprout was used as a new healthy vegetable. Since cultivation of peanut is thrived in the reclaimed sandy soil, thus, great attention should be attained to increase its cultivation in reclaimed sandy soil. Reclaimed sandy soil mostly suffer from different environmental adverse conditions such as, nutrient shortage, low availability of water, fluctuation of temperature between day and night and high irradiances3. Therefore, it is very important to increase peanut tolerance to these unsuitable environmental conditions through several strategies. These strategies include selection of high tolerance new genotypes with high yielding ability, applying the most effective agricultural practices and/or using external application with different natural growth promoting substances. Promoting substances as plant growth regulators, amino acids, vitamins and antioxidants etc., which offer a great opportunity to improve growth and productivity of peanut plant.
Amino acids are one of these important natural compounds used in promoting growth and productivity of various crops4. One of these amino acids is L-tyrosine. The L-tyrosine is the hydroxyl phenol acid that is used to build hormones, proteins and used as an important source for different plant components. It is considered as precursors of thousands of vital and specialized compounds in plant cells. It plays a vital role for tyrosine-derived metabolites, like vitamin-E, plant phenolic compounds, cyanogenic glycosides and suberin which have crucial roles in plant fitness5. Moreover, it has a role in signaling cascades by acting as signal molecules or by mediating the conjugation between amino acids and phytohormones to change hormone levels6. They can act as stress-reducing agents7-9. Earlier researcher has shown the efficiency of amino acids uptake by plants10-12.
Another natural produced compound in plants is salicylic acid (SA), it presents slightly in plant cells. The SA plays a vital role for improving response of plants against various environmental stressors where act as a hormone-like substance and a signaling or messenger molecule in plant. It also plays a positive vital role for improving ion uptake and transport, permeability of membrane, rate of photosynthetic, transpiration, plant growth and development13,14. Senaratna et al.15 reported that the effect of SA depends on its concentration, method and time of application, environmental conditions, plant species and plant growth stage. Many studies reported that foliar application of SA has been shown to enhance plant growth as well as biomass and yield in a variety of plant species16-19. So, the present work was designed in order to compare between the potential effects of different applied tyrosine at 0, 50, 100 and 150 mg L–1 and salicylic acid at 0, 100, 2100 and 300 mg L–1 on the vegetative growth, some biochemical aspects, yield and quantity and quality of peanut plants.
MATERIALS AND METHODS
Two field experiments were conducted at the Experimental Farm of National Research Center, (latitude 30°30'1.4"N, longitude 30°19'10.9"E and 21 m+MSL (mean sea level) at (NRC), Al Nubaria district, El-Beheira Governorate, Egypt, during 2 successive summer seasons of 2018 and 2019 to study the physiological role of tyrosine and salicylic acid foliar treatment on vegetative growth, photosynthetic pigments, yield and its components as well as seed quality of peanut under sandy soil conditions.
The experimental soil (0-30 depth) was analyzed according to the method described by Jackson20. Soil texture was sandy and having the following characteristics: Sand 94.7%, pH 8.6, organic matter 0.8%, CaCO3 2.4%, EC 0.13 mmhos cm–3, available N 18.0 ppm, available P 18.0 ppm, available K 104 ppm and available Zn 0.05 ppm.
The experimental design was complete randomized block design in 3 replications, where the antioxidant two materials were used as foliar applications at rates of tyrosine (0.0, 50, 100 and 150 mg L–1) and salicylic acid (0.0, 100, 200 and 300 mg L–1) were randomly applied twice, after 30 and 45 days from sowing date. The plot area was 10.5 m2 consisting of five rows (3.5 m length and 60 cm between rows).
Peanut (Arachis hypogaea L.) variety Gize-6 were procured from Oil Crops Research Department, Field Crops Research Institute, Agricultural Research Center, Giza Egypt. It was inoculated just before sowing with the specific rhizobium bacteria inoculants. Seeds of peanut were sown in the first week of May, 2018 and 2019. Phosphorus fertilizer, as calcium superphosphate (15.5% P2O5) was added during the seed bed preparation at rate of 146.4 kg P2O5 ha–1. Potassium sulphate (48% K2O) at the rate of 120 kg ha–1 was applied at sowing. Nitrogen fertilizer was added at a rate of 72 kg N ha–1 as ammonium sulfate (20.60% N) in 2 equal doses, the first half at sowing and the second after 30 days later.
The normal cultural practices for groundnut were applied as recommended in the district. Sprinkler irrigation was applied as plants needed. Groundnut was manually harvested on September 25th at both seasons.
Recording of data: The data pertaining to morphology of vegetative growth, photosynthetic pigments, yield components and seed oil percentage.
Vegetative growth: A random sample of 5 plants were randomly taken from each plot to determine growth parameters at 60 days after sowing i.e., shoot and root length (cm), branches (number/plant), shoot fresh and dry weights (g/plant), root length (cm), root fresh and dry weights (g/plant).
Yield and yield components characters: A random sample of 5 plants was assigned for investigation in each plot. The plants were taken from the middle region of the plot at harvest time, data on yield characters were recorded as follows.
Number of branches/plants, straw yield/plant (g), pods yield/plant (g), biological yield/plant (g), number of pods/plants, number of seeds/pods, seed yield/plant (g). Whole plot was harvested and the pods were air dried to calculate biological yield (t ha–1), seed yield (t ha–1) and oil yields were calculated t ha–1.
Chemical analysis
Shoot system
Photosynthetic pigments: Total chlorophyll a, b and carotenoids contents in fresh leaves were estimated using the method of Lichtenthaler and Buschmann21. Total carbohydrate was carried out according to Prud'homme et al.22. Indole acetic acid content was extracted and analyzed by the method of Larsen et al.23. Total phenol content was measured as described by Danil and George24. The extraction and assay of phenylalanine ammonia lyase (PAL, EC, 4.3.1.1) and tyrosine ammonia lyase (TAL, EC, 4.3.1), enzymes activities were carried out according to the method adopted by Beaudoin-Eagan and Thorpe25.
Seeds: Seed oil content was determined by using Soxhlet extraction apparatus using petroleum ether as a solvent and then the seed oil percentage was calculated on dry weight basis according to AOAC26. Analysis of fatty acids was determined from seed oil specimens of the second season according to Vogel (1975). The GLC was carried out under the same conditions27. Carbohydrate (%), flavonoids contents were determined by the aluminum chloride colorimetric assay as described by Ordonez et al.28, The method used for determination of lycopene and β-carotene as described by Nagata and Yamashita29 and DPPH was determined according to Gyamfi et al.30.
Statistical analysis: All data were statistically analyzed according to Snedecor and Cochran31. The least significant differences (LSD5%) were used to compare the means.
RESULTS
Growth parameters: Different treatments of foliar applications of tyrosine (50, 100 and 150 mg L–1) and salicylic acid (100, 200 and 300 mg L–1) caused significant and gradual increases in different growth criteria (Shoot and root length, branches number/plant, shoot, root fresh and dry weight) up to 100 mg L–1 tyrosine and 200 mg L–1 salicylic acid thereafter the different studied criteria values decreased but still greater than control plants (Table 1). Data clearly showed that, 100 mg L–1 tyrosine and 200 mg L–1 of salicylic acid were the most effective concentration for the most of studied growth criteria. Application of 100 mg L–1 tyrosine increased shoot length, branches number/plant, shoot fresh and dry weight, root length, fresh and dry weight by 65, 70, 355, 254, 37, 137 and 125%, respectively. Foliar treatment of tyrosine was more effective than salicylic acid on increasing the most studied growth criteria of peanut plants.
| Table 1: | Effect of tyrosine and salicylic acid application on growth criteria of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error, data are means of 2 seasons | |
| Table 2: | Effect of tyrosine and salicylic acid application on photosynthetic pigments (μg g–1 fresh weight) of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error | |
| Table 3: | Effect of tyrosine and salicylic acid application on total carbohydrate (%) (CHO), IAA (μg/100 g fresh weight and phenolic contents (mg/100 g dry weight) of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error | |
| Table 4: | Effect of tyrosine and salicylic acid application on PAL and TAL (U min–1 g–1/fresh weight) of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error | |
Photosynthetic pigments: Data in Table 2 showed that tyrosine (50, 75 and 100 mg L–1) or salicylic acid foliar application (100, 150 and 200 mg L–1) caused significant increases in chlorophyll a and b, carotenoids and consequently total pigments of peanut plant.
Different concentrations of tyrosine treatments were more effective than salicylic concentrations on enhancing different photosynthetic pigments. The highest positive effect was obtained from 200 mg L–1 of salicylic acid application in chlorophyll a meanwhile tyrosine with 150 mg L–1 has the highest increased effect on chlorophyll b, carotenoids and total pigments contents.
Indole acetic acid (IAA), total carbohydrates and phenolic contents: Data in Table 3 showed that, foliar application of L-tyrosine (i.e., 50, 75 and 100 mg L–1) or salicylic acid (100, 200 and 300 mg L–1) caused significant increases in IAA, total carbohydrates and phenolic contents of peanut plant as compared with untreated plants. The most pronounced treatment was 100 mg L–1 tyrosine on increasing IAA, total carbohydrates and phenolic contents as compared with other used treatments.
Phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) enzymes: The changes in activities of PAL and TAL enzymes of peanut plant affected by external treatment of tyrosine or salicylic acid different concentrations were recorded in Table 4. Data showed that, foliar treatment of tyrosine (50, 75 and 150 mg L–1) or salicylic acid (100, 200 and 300 mg L–1) increased significantly PAL and TAL activities as compared with untreated plants. The most effective treatment on increasing PAL and TAL enzyme activities was 100 mg L–1 tyrosine as compared with different treatment.
| Table 5: | Effect of tyrosine and salicylic acid application on yield, yield components of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error, data are means of 2 seasons | |
| Table 6: | Effect of tyrosine and salicylic acid application on biological, seed and oil yields and carbohydrate (%) of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error, data are mean of 2 seasons | |
Yield and its components: Data in Table 5 and 6 clearly showed that, different treatments significantly increased peanut yield and its components such as branches, pods (number/plant), seeds (number/pod), biological, straw, pods and seeds weight (g/plant, Table 5), biological, seed and oil yield (kg ha–1, Table 6) as compared to control treatment. The maximum increases in biological, seed and oil yield (kg ha–1) were obtained in response to foliar application of 100 mg L–1 of tyrosine. Application of 100 mg L–1 tyrosine treatment came in the first order followed by 200 mg L–1 salicylic acid for more values of peanut yield and its components compared to the other treatments. The percentages of increases in biological, seed, oil yield (t ha–1) and oil (%) were 80.46, 116.29, 144.93 and 14.45% in response to 100 mg L–1 tyrosine (Table 6), meanwhile these percentages were 73.56, 83.69, 110.25 and 13.10%, respectively in response to 200 mg L–1 salicylic acid (Table 6).
Nutritional value, antioxidant compounds and antioxidant activities of peanut seeds: The changes of some nutritional contents (total carbohydrates and oil percentages), antioxidant compounds (flavonoids, β-carotene and lycopene) and antioxidant activities (as DPPH%) are recorded in Table 7. Data clearly showed the improving effect of different external treatments either tyrosine or salicylic acid on peanut quality of yielded seeds. The L-tyrosine different concentrations (50, 100 and 150 mg L–1) and salicylic acid (100, 200 and 300 mg L–1) increased significantly carbohydrate (%), oil (%), flavonoids, β-carotene, lycopene contents as well as the DPPH activities of the yielded seeds of peanut plants as compared to untreated plants. Peanut treatment with 100 mg L–1 was the most effective treatment as it gave the highest increases in all the above-mentioned parameters (Table 7).
Fatty acid composition: Gas chromatographic analysis of methyl esters of fatty acids of the yielded peanut oil showed that foliar spray of different concentration of L-tyrosine or salicylic acid improved fatty acid constituents via increasing unsaturated fatty acids and decreased saturated fatty acids as compared with untreated plants (Table 8). So, the ratio of total unsaturated (TU)/total saturated (TS) was increased. Palmitic acid (C16:0) was the predominant saturated fatty acids, followed by stearic acid (C18:0) meanwhile, oleic acid (C18:1) and linoleic acid (C18:2) were the most abundant fatty acids in all treatments. Moreover, oleic/linoleic and total unsaturated total saturated were increased in response of different concentrations of tyrosine or salicylic acid.
| Table 7: | Effect of tyrosine and salicylic acid application on carbohydrate (%), oil (%), flavonoids, β-carotene, lycopene (μg g–1) and DPPH (%) activity of the yielded seed of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error | |
| Table 8: | Effect of tyrosine and salicylic acid application on fatty acids contents of the yielded seed of peanut plant grown under sandy soil |
Each value represents the mean of 3 replicates±standard error, C16:0: Palmitic acid, C18:0: Stearic acid, C20:0 Arachidic acid, C18:1: Oleic acid, C18:2: Linoleic acid, C18:3: Linolenic acid, TS: Total saturated fatty acid, TUS: Total unsaturated fatty acid, TFA: Total fatty acid, TU/TS: Total unsaturated/total saturated fatty acid | |
DISCUSSION
Foliar treatment of tyrosine or salicylic acid increased growth criteria of peanut plant grown under sandy soil (Table 1). Application of tyrosine or salicylic acid increased growth values of peanut plant through increasing photosynthetic pigments (Table 2) and endogenous promoters especially IAA and carbohydrate contents (Table 3). These responses of tyrosine and salicylic acid treatments could be attributed to the increased levels of endogenous hormones consequently stimulation of cell division and/or cell enlargement and subsequently improved growth. Similar to the results of tyrosine32-34.
A notable increase of photosynthetic pigments was detected in peanut grown under sandy soil treated with either L-tyrosine or salicylic acid is represented in (Table 2). These results of amino acid treatment were confirmed by the earlier findings on different plant species16,34,35. The positive role of L-tyrosine on improving chlorophyll a and b, carotenoids contents might be due to the succinyl COA (Kreb's cycle intermediate) as well as, it enhances the biosynthetic pathway leading to chlorophyll formation36. Dawood et al.19 stated that, salicylic acid application significantly increased chlorophyll a and b, carotenoids and total chlorophylls of flax plant. Moreover, the potential effects of salicylic acid and its precursors' L-tyrosine amino acid may be attributed to the decrease in chlorophyll loss due to its ability to increase the antioxidant capacity of plant or inducing the synthesis of stabilizing substances37.
The increases in total carbohydrates contents of peanut plant treated with either tyrosine or salicylic acid showed the same trend obtained previously on vegetative growth and photosynthetic pigments. These results are in agreement with the finding of other studies on different plants38,39. In addition, the increases in total carbohydrates might be related to the increased photosynthetic pigments which increase the rate of photosynthesis and carbohydrate synthesis40.
Foliar application with different concentrations of tyrosine or salicylic acid caused significant increases in IAA contents. It is obvious that, the increases in endogenous IAA content concurrent with the increase in growth rate (Table 1) and this confirmed the role of the endogenous hormones in inducing cell division and/or cell enlargement and subsequently enhancing plant growth41-43. Moreover, the increased IAA contents could be attributed to the enhancing of biosynthesis and/or decreases their degradation and conjugation19.
External treatment of tyrosine or salicylic acid increased significantly phenol contents of peanut plant. Tyrosine, is claimed to have an enhancing effect on phenolic substances. This enhancing role on different plants44,45. Also, Heldt and Piechulla46 stated that phenolic compounds are derived from amino acids thus treatment with salicylic acid and its precursor increased total phenolic contents. Moreover, the increases in phenolic contents in plants treated with salicylic acid could be due to the phenolic nature of this compound17. Therefore, it could be expected that their application on plants increased phenolic concentration as previously confirmed on linseed plant12, on soybean17 and on lupine plant39.
Phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) are considered regulatory enzymes in the phenylpropanoid pathway. PAL is one of the key enzymes in controlling phenolics biosynthesis from phenylalanine. Also, TAL, another enzyme involved in phenols synthesis47. Different treatments of tyrosine and SA increased PAL and TAL activities (Table 4). The obtained data are in agreements with those obtained48 on sweet basil plant. The obtained data showed that secondary metabolites in plants could be accumulated by inducing the phenylpropanoid pathway without any stresses48-51.
The improving in yield and its components of peanut plant by L-tyrosine or SA treatment might be resulted from the increases in growth (Table 1), photosynthetic pigment contents (Table 2) which could lead to increases in the photosynthesis process resulting in greater transfer of photo-assimilates to seeds and causing increases in their weights which resulted in increased number of branches/plant, pods and seeds number/plant and seed yield/plant (Table 5). In addition, the increase in yield might be due to the increase endogenous hormones (Table 3). It is evident that plant growth regulators seemed to form sink mobilizing the different nutrients, which are involved in building new tissues in wheat plants and/or enhance photosynthesis16. In addition, SA positively affects ion uptake and transport, membrane permeability and transpiration14, photosynthetic and growth rates52, increases CO2 assimilation likely responsible for the increased plant growth53. Moreover, salicylic acid (SA) as a natural signal molecule, has been shown to play an important role in regulating a number of physiological processes in plants. Its exogenous application has promoted plant performance under biotic and abiotic stresses15.
Different concentrations of tyrosine or salicylic acid increased significantly and gradually carbohydrate and oil contents of peanut seeds. Application of tyrosine on basil has resulted increase total oil. Similarly, salicylic acid treatment increased the nutritive value of linseed, soybean and flax plants respectively16,17,54. The promotive effect of tyrosine and salicylic acid could be resulted via their effects on enzymatic activity and translocation of the metabolites to the developed peanut seed. The substantial increase in carbohydrate contents could be resulted by the increased photosynthetic machinery due to the promotive effects of the used treatment on photosynthetic process. The increment in oil contents might be due to the increase in vegetative growth and nutrients uptake55.
Antioxidant compounds (flavonoid, β-carotene and lycopene contents) levels increased in peanut seeds in response to different tyrosine and salicylic acid (Table 7). Such increases might be due to the phenolic nature of salicylic acid and its precursor tyrosine56. So, it might be deduced that their external treatment on plants induced flavonoid and phenolic increases as reported earlier on linseed16. Lycopene is considered a non-photosynthetic pigment which is an important phytochemical and it is well known for its significant potential to serve as a remarkable antioxidant molecule57. Other important assigned functions imparted by lycopene include cell signaling and communications58 modulation of hormonal and immune response and role in metabolic pathways59. In addition, carotenoids are intimately linked with photosynthesis as a part of the light harvesting system, thus, under our prevailing experimental conditions the increases in lycopene and β-carotene contents may relate to the increase in photosynthetic processes (Table 2). With respect to free radicals scavenging activity (DPPH) which play an important role in scavenging increased level of free radicles which cause oxidative damage in plant cell.
The promotive effect of either tyrosine or salicylic acid on fatty acids constituents of peanut yielded oil (Table 8) are quite concurrent with those obtained using salicylic acid on flax plant16,54. The decreases in saturated fatty acids accompanied with the increases in unsaturated fatty acids enhanced oil quality60. The increases in saturated fatty acids (oleic and linoleic acids) of peanut was proved to improve oil quality and these fatty acids are essential for human diet as they lower the risk of heart diseases related to cholesterol oxidation as well as, decrease low density lipoprotein (LDL) in human blood16.
SIGNIFICANCE STATEMENT
This study explores the beneficial effect of treatment with tyrosine or salicylic acid on peanut plants grown under reclaimed sandy soils. It also, explain some physiological aspects of these compounds and their correlation with capability of plants to facing unfavorable conditions at reclaimed sandy soils. This study will help the researcher to understand the role of these compounds on peanut plants grown under field conditions. However, further studies must be done to evaluate the physiological effects of either tyrosine or salicylic acid on peanut plant grown under reclaimed sandy soil at molecular level (i.e., enzyme, protein picture...etc).
CONCLUSION
The results showed that, foliar application of different concentrations of L-tyrosine (50, 75 and 100 mg L–1) or salicylic acid (100, 200 and 300 mg L–1) enhanced all studied growth criteria as well as photosynthetic pigments, total carbohydrates, IAA and phenol contents in addition to yield and its components. Moreover, some nutritional contents (total carbohydrates and oil (%)), antioxidant compounds (flavonoids, β-carotene and lycopene) and antioxidant activities (as DPPH (%)) of the yielded peanut seeds. It could be conclude that L-tyrosine and SA can play important roles to promote growth and productivity of peanut plant especially in claimed sandy soil via regulating physiological and biochemical processes.