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Article

Effects of Exogenous Antioxidant Melatonin on Physiological and Biochemical Characteristics of Populus cathayana × canadansis ‘Xin Lin 1’ under Salt and Alkaline Stress

by
Runxian Song
1,
Faujiah Nurhasanah Ritonga
1,
Haiyang Yu
1,
Changjun Ding
2,* and
Xiyang Zhao
1,3,*
1
State Key Laboratory of Tree Genetics and Breeding, Forestry College, Northeast Forestry University, Harbin 150040, China
2
State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
3
Jilin Provincial Key Laboratory of Tree and Grass Genetics and Breeding, College of Forestry and Grassland, Jilin Agricultural University, Xincheng Street No. 2888, Changchun 130000, China
*
Authors to whom correspondence should be addressed.
Forests 2022, 13(8), 1283; https://doi.org/10.3390/f13081283
Submission received: 21 June 2022 / Revised: 26 July 2022 / Accepted: 10 August 2022 / Published: 13 August 2022
(This article belongs to the Special Issue Biotic and Abiotic Stress Effects on Tree Growth and Wood Properties)
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Abstract

:
Salt and alkaline stress is one of the important problems restricting agricultural production and afforestation projects. This kind of stress will greatly limit the growth and development of forest trees. Recently, melatonin has been gradually realized as a strong kind of antioxidant due to its important regulatory and protective roles in the process of plant growth and development. This study takes Xin Lin 1 (Populus cathayana × canadansis ‘Xin Lin 1’) as the research object, and measures the changes of physiological indexes at different time points to verify the alleviation effect of melatonin under salt and alkaline stress. In this experiment, plants have different behaviors in the face of different levels of exogenous melatonin. Among them, low concentrations of melatonin (50 μM and 100 μM) were more helpful to reduce the levels of MDA and osmotic regulators in leaves. At this level, the SOD and CAT content in the leaves increased significantly. Melatonin at 800 μM was more inclined to induce POD, but its activity was not significantly induced. Overall, melatonin contributes to the secretion of ABA in plants and has a tendency to inhibit the content of SA. It is worth mentioning that the 100 μM melatonin treatment was more conducive to the secretion of IAA. To sum up, this experiment proves that melatonin has a dose effect in alleviating stress.

1. Introduction

Poplar (Populus spp.) is a forest plant found in the boreal temperate zone of the Northern Hemisphere. This tree species has a fast growth rate and high biomass, and is one of the most important candidate tree species in afforestation projects [1]. Poplar not only has a small and complete genome, such as Populus trichocarpa [2], but also has strong genetic transformation ability. At present, Poplar has become a model tree species in forest tree research.
Salt and alkaline stress is one of the important problems restricting agricultural production and afforestation projects. In fact, compared with salt stress, alkali stress has a higher degree of harm. It can induce severe oxidative stress in forest trees. The free radicals generated by this reaction not only alter the microstructure of the chloroplast, reducing light and efficiency. It also acts on lipids to produce malondialdehyde (MDA). This ultimately affects the growth and development of poplar [3]. In order to alleviate the damage caused by stress, plants often enhance their own antioxidant enzyme activities. The content of soluble small molecules [4] has been shown to eliminate the damage caused by free radicals and salt and alkaline stress [5]. Therefore, many studies have pointed out [6,7] that physiological indicators such as antioxidant enzymes, malondialdehyde (MDA), soluble sugar, soluble protein, proline, and chlorophyll are important criteria for evaluating the resistance of seedlings.
Plant hormones refer to a type of organic substance that is synthesized in plants, which can be transported from the production site to the action site. They have a physiological effect on the plant body at a trace concentration [8]. At present, the academic community mainly classifies them into irritability hormones and growth-promoting hormones according to their roles [9]. All plant hormones will play a signaling role in plants and help them to cope with complex environmental changes at different stages of plant growth.
Melatonin is an indole-like small molecule compound with high lipophilicity and partial hydrophilicity [9]. Based on numerous results from previous studies, it was believed that this substance has important regulatory and protective roles in the process of plant growth and development [10]. In recent years, although there have been many studies on the use of exogenous melatonin to alleviate stress in plant’s study [11,12], most of the research objects focus on agricultural crops [13,14,15]. In the field of forestry, the lack of relevant research still limits our understanding of the function of melatonin. In this study, the content of related physiological and biochemical indicators such as chlorophyll (Chl), proline (Pro), soluble sugar (sSUG), soluble protein (sPRO), MDA, antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), growth-promoting hormones such as auxin (IAA), cytokinin (CTK), gibberellin (GA), and irritability hormones including abscisic acid (ABA) and salicylic acid (SA) were measured. We explore the changes of exogenous melatonin on indicators under salt and alkaline stress. It provides a theoretical basis for using melatonin to alleviate the salt and alkaline stress of trees.

2. Materials and Methods

The research object is Xin Lin 1 (Populus cathayana × canadansis ‘Xin Lin 1’) from Xinmin City, Liaoning Province, China. This poplar clone was collected in early April 2021 at Xinmin State-owned Mechanical Forest Farm (N 42°00′17.02″, E 122°81′07.74″, 40.1 m above sea level) in Liaoning Province, China. Hardwood cuttings technology was used and annual or biennial, woody stems (0.8~1.0 cm in diameter) without pests and diseases were chosen. We ensured that each cutting had double buds (color is tan) and cut them into 10 cm branches in early April. Then, each cutting was inserted into a plastic pot.
This experiment started on June 1st and we adopted the pot experiment method. First, a layer of non-woven fabric was lain on the bottom of each plastic pot. Second, the sterilized humus soil and garden soil was mixed at a ratio of 1:1 as a potting substrate. The height of the plastic basin and the diameter of the upper mouth were both 25 cm, and the substrate was flush with the upper mouth. Seedlings that grew taller than 60 cm were chosen. Every 6 plastic pots were put into the same plastic box, and each group contained 6 boxes. Melatonin was dissolved in alcohol and distilled water, and then prepared into six gradients (0, 50, 100, 200, 400, 800 μM), respectively. In this experiment, 0 μM was set as the control group (CK). Exogenous melatonin solutions of 6 concentrations were sprayed on the leaves by an agricultural lithium battery high pressure swirl sprayer (using the air atomizing nozzles, Dv0.5 < 500 μM). The spraying degree should reach the tip of the leaves. The next day, the samples in each group were supplemented with 120 mM/L NaCl and Na2CO3 salt solution and nutrient solution. This process was repeated three days before the first sampling, every 3 days. In order to better simulate the local soil environment of Xinmin (pH 7.5~8.0), the pH of the soil in each pot was detected. The detection site in the pot was 7 cm from the soil in the pot. Five sites were set up in each pot to be assayed. distilled water was added to the test site until the bottom was in a muddy state. The pH meter probe was inserted to check the soil pH in the pot, and we waited until the average pH in each pot reaches 7.7.
The whole experiment was carried out in a greenhouse. The temperature of the greenhouse was controlled at about 24 °C at night and 30 °C during the day, the relative humidity was maintained at about 60%, and the photosynthetically active radiation intensity was about 150 μmol (m−2 s−1). After the experiment was run for 10 days, the first sampling was carried out, followed by sampling every 4 days for 5 rounds (see Figure 1). Fresh samples were frozen in liquid nitrogen immediately after collection and then stored at −80 °C refrigerator until use.

2.1. Measurement of Physiological Indicators

In this experiment, we used the ELISA kit provided by Shanghai Enzyme Link Biotechnology Co., Ltd. (Shanghai, China) to measure the content of POD, SOD, CAT, MDA, sPRO, sSUG, proline, chlorophyll, GA, ABA, IAA, CTK and SA.
First, the samples (30 Hz, 90 s) were ground to powder using a grinder (MM400, Retsch) (Düsseldorf, Germany). Then, 100 mg of the powder was weighed from each sample and dissolved in 1.2 mL of a 70% methanol solution. The supernatant was extracted using a centrifuge (12,000 rpm, 20 min). Then it was pre-coated with POD, SOD, CAT, MDA, sPRO, sSUG, proline, chlorophyll, GA, ABA, IAA, CTK, and SA antibody. Samples, standards, and HRP-labeled detection antibodies were added to the microwells in sequence, incubated, and washed thoroughly. Tetramethylbenzidine (TMB) underwent a color reaction, and the TMB of each group turned blue under the catalysis of peroxidase, and turned yellow under the action of acid. There is a positive correlation between the shade of color and the content of antioxidant enzymes in the samples. Finally, the absorbance (OD value) was measured at a wavelength of 450 nm using a microplate reader (Infinite F50) (Tecan: Männedorf, Switzerland)).

2.2. Statistical Analysis

This experiment used Microsoft Excel 2017 and SPSS 23 statistical software for statistical analysis. All data are presented as mean ± standard error (SE). To test for significant differences between indicators, we used a two-way ANOVA with 0.05 as the significance indicator, and analyzed it through R’s ggplot2 [16], ComplexHeatmap [17], and ggcor (https://github.com/hannet91/ggcor (accessed on 19 March 2020)) package to draw the resulting picture.

3. Results

3.1. Changes of Antioxidant Enzymes under the Influence of Different Doses of Melatonin

The changes of antioxidant enzyme activities of each experimental group at different time points are shown in Figure 2. With the prolongation of treatment time, the POD content of each experimental group showed an upward trend, the SOD content showed a downward trend, and the CAT content fluctuated. From the perspective of melatonin application dose, the SOD and CAT contents under 100 μM treatment were significantly higher than those in the control group, in which SOD reached the highest value (2148.54 U/g) in the T5 stage (26 days), and CAT in the T4 stage (22 days) reached the highest value (880.04 U/g). On the contrary, the POD content under 100 μM treatment was relatively low, and this index reached the lowest point in the experimental group at the T4 stage (22 days), which was 59.6% of the control group at the same period.

3.2. Changes of Osmotic Regulators under the Influence of Different Doses of Melatonin

The changes in the content of osmotic regulators in each experimental group at different time points are shown in Figure 3. With the extension of time, the content of soluble sugar and soluble protein showed a trend of first a decrease and then an increase, while the change of proline showed the opposite trend. The soluble sugar of each experimental group reached the lowest value on the 18th day of the experiment, and the soluble protein usually reached the lowest value on the 14th day. It is worth noting that in these three indicators, the average content of the 50 μM and 100 μM experimental groups was significantly lower than that of the control group. The average content of the 800 μM experimental group was slightly higher than that of the control group.

3.3. Changes of MDA and Chlorophyll under the Influence of Different Doses of Melatonin

In order to detect the alleviating effect of melatonin on stress, we systematically analyzed the changes of MDA and chlorophyll content in each experimental group, as shown in Figure 4. The change trend of MDA in each experimental group showed a trend of first an increase and then a decrease. It was clearly shown that 50 μM and 100 μM melatonin had the best alleviation effect. The result of 800 μM was slightly higher than that of the control group, indicating that the high concentration of melatonin aggravated the stress effect. Furthermore, the change of chlorophyll showed a trend of first a decrease and then an increase. The chlorophyll content of each experimental group usually reached the lowest value in the T3 stage (18 d) or T4 stage (22 d) of the experiment.

3.4. Effects of Different Doses of Melatonin on Plant Growth-Stimulating Hormones

Figure 5 shows the effect of exogenous melatonin on growth-promoting hormone in plants under stress. Relatively speaking, the three growth-promoting hormones showed a decreasing trend. Compared with the control group, the treatment of each experimental group increased the auxin level in the plant and inhibited the level of GA and CTK. Among them, 100 μM and 800 μM had the most significant effects on the levels of three endogenous hormones. The treatment effect of 400 μM melatonin was not obvious. Finally, it is worth noting that the plants treated with 100 μM of exogenous melatonin had a tendency to exuberantly secrete IAA.

3.5. Effects of Different Doses of Melatonin on Plant Irritability Hormones

The effects of different doses of melatonin on irritability hormones in plants are shown in Figure 6. In general, with the extension of time, the ABA in plants showed a fluctuating and increasing trend. Among them, 50 μM, 100 μM, and 800 μM melatonin treatment produced more intense stimulation to plants. From the results, exogenous melatonin can effectively stimulate the secretion of abscisic acid and inhibit the secretion of SA in plants under a stress environment.

3.6. Correlation Analysis of Each Indicator

When the exogenous melatonin dose reached 100 μM, there was a significant positive correlation between growth-promoting hormones (GA, IAA, CTK), soluble regulators and antioxidant enzyme systems in plants, and stress hormones (ABA, SA) multiplied with it in the opposite situation. This correlation changed with the increase of the exogenous melatonin concentration. When the exogenous melatonin dose increased to 800 μM, there was a significant negative correlation between the growth-stimulating hormone and the antioxidant enzyme system. The correlation coefficient between and the soluble regulator also basically turned from positive to negative. The correlation coefficients between stress hormones and various physiological indicators showed an increasing trend, but the effect was not obvious. In addition, the correlation between the soluble regulator and the antioxidant enzyme system showed a positive correlation under the stimulation of low concentrations of melatonin, and it was weakened under the stimulation of high concentrations of melatonin.

4. Discussion

Soil salinization is one of the most dangerous environmental stresses faced by plants during growth [18]. Excessive NaCl will enter the plant through the corresponding carrier protein, breaking the balance of ion concentration inside and outside the cell, causing osmotic disorder, which will eventually lead to cell dehydration and osmotic stress. Alkaline stress caused by Na2CO3 will destroy the original intracellular pH homeostasis, and even change the membrane structure of cells in severe cases, affecting the absorption of nutrients by plants [19]. In recent years, many experiments have confirmed that saline-alkali stress can change the activity of antioxidant enzymes and the content of osmotic regulators in plants [20,21]. As an emerging antioxidant, melatonin can not only enhance the transcription efficiency of these antioxidant enzyme mRNAs by activating transcription factors in the promoter regions of antioxidant enzymes, but also through its cascade reactions, namely melatonin and its metabolites. It also has a free radical scavenging effect for the continuous protection of plants [22,23]. Zhan et al. [24] found that melatonin played an extremely important role in the pathway of plants corresponding to salt stress. Yan et al. [25] also found that melatonin can effectively improve the leaf phenotype of rice seedlings under salt stress.
Among all the physiological and biochemical indicators measured in this experiment, MDA is a basic parameter to measure the damage of the cell membrane under environmental stress [26]. Surprisingly, compared with the control group, 50 μM and 100 μM had the best alleviation effect on MDA content. Moreover, 800 μM treatment was slightly higher than the control group, which indicated that the experimental seedlings in this group received more stress than CK. Similarly, Xiao et al. [27] also found that the increase of melatonin can significantly increase the MDA content in cotton. Lv et al. [28] found that 100 μM treatment can significantly reduce environmental stress to Tartary buckwheat.
Previously, several studies have shown that salinity and alkali stress can alter the activity of plant antioxidant enzymes [29,30,31]. Normally, SOD can decompose ROS into H2O2. H2O2 is decomposed into H2O and O2 under the action of POD and CAT [32,33]. In this experiment, different doses of exogenous melatonin were used to alleviate the stress of “Xin Lin 1” growing in saline-alkali soil. The results showed that 50 μM and 100 μM melatonin could significantly increase SOD and CAT activities in leaves, and 800 μM melatonin was more inclined to induce POD, but its activity induction was not significant, and it tended to inhibit CAT activity. In addition, the secretion laws of the three enzymes fluctuated with time, among which SOD and CAT fluctuated the most. Our finding was in accordance with previous studies [34]. The Jiang et al. [35] study also showed that low concentration of exogenous melatonin can significantly enhance the antioxidant enzyme activity in plants.
Furthermore, plant cells increase the intracellular water potential by accumulating small organic molecules such as proline, soluble sugar, and soluble protein to maintain their own water retention capacity [36,37]. In this experiment, different doses of exogenous melatonin could significantly change the accumulation level of related substances. The content of osmotic regulators induced by low levels of melatonin (50 μM, 100 μM) was significantly lower than that of the control group. This indicated that under the induction of low concentrations of melatonin, the stress intensity of plants was reduced. As an important indicator for judging the level of oxidative stress in plant cells [38], the results of proline showed that the treatment effect of 100 μM was better than that of 50 μM. On the 22th day of the experiment, the proline content induced by 100 μM was 58% of that induced by 50 μM. In contrast, the 800 μM treatment group induced slightly higher osmolyte levels than the control group. Chlorophyll is an important pigment that absorbs light energy during photosynthesis in higher plants [39]. In this experiment, its variation law is presented with fluctuations. Our result was in accordance with previous studies in Brassica juncea [40] and kiwifruit [41].
The change of hormone content is an important factor affecting the growth and development of plants under saline-alkali stress [42]. Saline-alkali stress usually inhibits the secretion of growth-promoting hormones such as IAA in plants [43], and plants usually rely on the secretion of stress hormones such as ABA to cope with stress [44]. The results of this experiment show that melatonin can stimulate the secretion of abscisic acid in plants under a stress environment, and has the tendency to inhibit the secretion of SA. This is similar to the result of Imran et al.’s [45] study. In addition, 100 μM melatonin treatment is more conducive to the secretion of plant IAA.
In conclusion, the 800 μM treatment enhanced the coupling between various physiological indicators as a whole. In particular, the correlation between antioxidant enzyme systems and osmotic regulators, as well as stress hormones, was enhanced. The opposite was true for the 100 μM treatment; in particular, a negative correlation was observed between MDA and osmolyte (see Figure 7). Therefore, we can judge that exogenous melatonin has a dose effect on the physiological indicators of poplar under saline-alkali stress (see Figure 8). Relative to CK, the low-concentration experimental group (50 μM, 100 μM, 200 μM) could significantly relieve stress, while the high-concentration dose (800 μM) of melatonin seemed to have the opposite effect. Similar findings were also found in the study by Lv et al. [46].

5. Conclusions

Saline-alkali stress can inhibit the growth and development of forest trees, especially poplar, a fast-growing and high-yield timber species. Although melatonin has been shown to alleviate recent salinity stress in crops, detailed data are still lacking in forestry related research. Therefore, the melatonin-mediated alleviation of ophthalmic alkali stress in poplar was explored. In this study, the experimental group and the control group were set up to be stressed with a solution of 120 mM/L NaCl and Na2CO3, and six concentration gradients were set at the same time. After analyzing eight common physiological indicators and five hormonal indicators, we found that melatonin had a significant dose effect in the process of alleviating saline-alkali stress. In the face of oxidative damage caused by saline-alkali stress, the regulation effect of low concentrations of melatonin (50 μM and 100 μM) was more significant. This dose was therapeutic, the levels of osmotic regulators and MDA in leaves were significantly reduced, and the activities of related antioxidant enzymes (SOD, CAT) were significantly increased. In contrast, the induction effect of high concentrations of melatonin was not obvious. In terms of hormone regulation, melatonin not only promotes the secretion of ABA. Furthermore, IAA secretion was also induced under low-concentration treatment conditions. Therefore, this study provides new clues in using different levels of melatonin to alleviate the salinity-alkali stress of forest trees. Our findings contribute to the development of a practical approach to sustainable forestry in saline lands.

Author Contributions

R.S. contributed to writing and original draft preparation, R.S. and H.Y. conducted the experiment, F.N.R. and H.Y. edited the manuscript, and C.D. and X.Z. contributed to supervision, project administration, funding acquisition, review, and editing the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This paper was funded by The National Key Research and Development Program of China (2021YFD2201204).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Acknowledgments

The authors appreciate the reviewers for comments and suggestions.

Conflicts of Interest

The authors report no declarations of interest.

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Figure 1. Illustration of the experiment’s method. The black flag indicates the day that the samples were treated with melatonin (the illustration can be used for all melatonin gradients); the green flag indicates the day that the samples were treated by NaCl and Na2CO3; the red flag indicates the day that the samples are collected.
Figure 1. Illustration of the experiment’s method. The black flag indicates the day that the samples were treated with melatonin (the illustration can be used for all melatonin gradients); the green flag indicates the day that the samples were treated by NaCl and Na2CO3; the red flag indicates the day that the samples are collected.
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Figure 2. Relative CAT, SOD and POD content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatment base on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of POD content, (b) changes of SOD content, (c) changes of CAT content.
Figure 2. Relative CAT, SOD and POD content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatment base on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of POD content, (b) changes of SOD content, (c) changes of CAT content.
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Figure 3. Relative soluble sugar, soluble protein, and proline content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatment based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of soluble sugar content, (b) changes of soluble protein content, (c) changes of proline content.
Figure 3. Relative soluble sugar, soluble protein, and proline content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatment based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of soluble sugar content, (b) changes of soluble protein content, (c) changes of proline content.
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Figure 4. Relative MDA and chlorophyll content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatments based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of MDA content, (b) changes of chlorophyll content.
Figure 4. Relative MDA and chlorophyll content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatments based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of MDA content, (b) changes of chlorophyll content.
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Figure 5. Relative IAA, CTK, and GA content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatments based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of IAA content, (b) changes of GA content, (c) changes of CTK content.
Figure 5. Relative IAA, CTK, and GA content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatments based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). (a) Changes of IAA content, (b) changes of GA content, (c) changes of CTK content.
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Figure 6. Relative ABA and SA content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatments based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). Letters such as a-f are used in this figure to indicate the degree of difference between groups (a) Changes of ABA content, (b) changes of SA content.
Figure 6. Relative ABA and SA content of Populus cathayana × canadansis ‘Xin lin 1’ leaves under control and different MT treatments based on salt and alkaline stress in different time periods of the experiment. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. Each value is the average ± standard error (±SE). For two-way ANOVA, the letters on the left represent the detection phase (p < 0.05) and the letters on the right represent the experimental concentrations (p < 0.05). Letters such as a-f are used in this figure to indicate the degree of difference between groups (a) Changes of ABA content, (b) changes of SA content.
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Figure 7. Correlation of physiological indexes of Populus cathayana × canadansis ‘Xin Lin 1’ under 100 μM (a) and 800 μM (b). The size of the solid square indicates the correlation degree, with blue representing positive correlation and red representing negative correlation. Images use *, ** and *** to indicate the significance between indicators. * means p value < 0.1; ** means p value < 0.05; *** means p value < 0.01.
Figure 7. Correlation of physiological indexes of Populus cathayana × canadansis ‘Xin Lin 1’ under 100 μM (a) and 800 μM (b). The size of the solid square indicates the correlation degree, with blue representing positive correlation and red representing negative correlation. Images use *, ** and *** to indicate the significance between indicators. * means p value < 0.1; ** means p value < 0.05; *** means p value < 0.01.
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Figure 8. (a) Heatmap of physiological indexes of Populus cathayana × canadansis ‘Xin lin 1’ under 100 μM and 800 μM for different time periods. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. (b) Effects of different doses of MT on various physiological indexes. Arrows indicate facilitation, flat arrows indicate inhibition. Black for 100 μM; red for 800 μM; POD, peroxidase; Chl, chlorophyll; Pro, proline; sSUG, soluble sugar; sPRO, soluble protein; MDA, malondialdehyde; SOD, superoxide dismutase; CAT, catalase; IAA, auxin; CTK, cytokinin; GA, gibberellin; ABA, abscisic acid; SA, salicylic acid.
Figure 8. (a) Heatmap of physiological indexes of Populus cathayana × canadansis ‘Xin lin 1’ under 100 μM and 800 μM for different time periods. T1 means 10 days, T2 means 14 days, T3 means 18 days, T4 means 22 days, T5 means 26 days. (b) Effects of different doses of MT on various physiological indexes. Arrows indicate facilitation, flat arrows indicate inhibition. Black for 100 μM; red for 800 μM; POD, peroxidase; Chl, chlorophyll; Pro, proline; sSUG, soluble sugar; sPRO, soluble protein; MDA, malondialdehyde; SOD, superoxide dismutase; CAT, catalase; IAA, auxin; CTK, cytokinin; GA, gibberellin; ABA, abscisic acid; SA, salicylic acid.
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Song, R.; Ritonga, F.N.; Yu, H.; Ding, C.; Zhao, X. Effects of Exogenous Antioxidant Melatonin on Physiological and Biochemical Characteristics of Populus cathayana × canadansis ‘Xin Lin 1’ under Salt and Alkaline Stress. Forests 2022, 13, 1283. https://doi.org/10.3390/f13081283

AMA Style

Song R, Ritonga FN, Yu H, Ding C, Zhao X. Effects of Exogenous Antioxidant Melatonin on Physiological and Biochemical Characteristics of Populus cathayana × canadansis ‘Xin Lin 1’ under Salt and Alkaline Stress. Forests. 2022; 13(8):1283. https://doi.org/10.3390/f13081283

Chicago/Turabian Style

Song, Runxian, Faujiah Nurhasanah Ritonga, Haiyang Yu, Changjun Ding, and Xiyang Zhao. 2022. "Effects of Exogenous Antioxidant Melatonin on Physiological and Biochemical Characteristics of Populus cathayana × canadansis ‘Xin Lin 1’ under Salt and Alkaline Stress" Forests 13, no. 8: 1283. https://doi.org/10.3390/f13081283

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