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Article

Pathways and Characteristics of Lead Uptake and Transportation in Rhus chinensis Mill

by
Wenxiang He
1,2,
Shufeng Wang
1,
Yangdong Wang
1,
Mengzhu Lu
2 and
Xiang Shi
1,*
1
Key Laboratory of Tree Breeding of Zhejiang Province, Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou 311400, China
2
State Key Laboratory of Subtropical Silviculture, Zhejiang A&F University, Hangzhou 311400, China
*
Author to whom correspondence should be addressed.
Forests 2023, 14(1), 90; https://doi.org/10.3390/f14010090
Submission received: 16 November 2022 / Revised: 31 December 2022 / Accepted: 1 January 2023 / Published: 3 January 2023
(This article belongs to the Section Forest Ecophysiology and Biology)
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Abstract

:
Rhus chinensis Mill is a potential plant for phytoremediation of Pb and is able to uptake a copious amount of Pb. However, little is known about the pathways and properties of Pb uptake in this plant. Here, controlled experiments were used to assess Pb uptake and translocation in R. chinensis. The whole time-kinetics of Pb uptake were divided into two stages: rapid uptake and slower accumulation, and the two processes were fitted with a linear model. The concentration-dependent kinetics of Pb uptake were characterized by a modified Michaelis–Menten equation. The Km and Vmax value of Pb influx in roots were 19.44 and 14.83, respectively. Transpiration inhibitors had no significant effect on the Pb concentration of root and shoot. Low temperatures (4 °C) and metabolic inhibitors (carbonyl cyanide m-chlorophenylhydrazone and 2,4-dinitrophenol) significantly reduced the Pb concentration in the roots and leaves of R. chinensis plants. Furthermore, the addition of calcium ion channel inhibitors and protein synthesis inhibitors significantly reduced the Pb concentration in the roots of R. chinensis plants. These results show that both active and passive processes of Pb uptake and translocation exist in the roots of R. chinensis plants. In addition, Pb uptake by the roots of R. chinensis plants was related to calcium ion channels.

1. Introduction

Lead (Pb) is the second most harmful heavy metal after arsenic [1]. Pb pollution in soil and water is mainly caused by human activities [2,3]. During the past 50 years, about eight million tons of Pb has been released into the environment [4]. Pb enters the food chain in multiple ways and ultimately threatens human health [5,6]. Therefore, the environmental pollution of Pb has attracted widespread attention.
Using plant-based remediation to remove heavy metals from the environment is cost-effective and can be applied persistently [7,8]. As the core part of remediation technology, hyperaccumulator plants are a hotspot of research in plant-based remediation in China and abroad [3] Pb in soil mainly exists in a divalent form, such as lead sulfide or lead oxide, and its chemical behavior is affected by many factors [1,9]. Pb usually has low mobility after entering the soil, which impedes its absorption by plants [10,11]. However, some hyperaccumulator plants can accumulate Pb in their bodies to a concentration of over 1000 mg kg−1 [2,12]. Thus far, multiple species of plants have been studied to elucidate the mechanism of heavy metal uptake by roots [8,13,14,15]. For example, Lu et al. [16] and Tao et al. [17] suggested that Cd uptake and translocation are active processes in a hyperaccumulating ecotype of Sedum alfredii, where a symplastic pathway plays an important contributes to root uptake, and xylem loading and translocation of Cd to the shoots. After Pb is adsorbed on the root surface, it may be transported into the inside of the root via the apoplast pathway [18]. The Casparian strip in the endodermis may impede the further movement of Pb [19]. In general, lead ions cannot pass through the Casparian strip [18]. However, some studies have shown that the stress caused by high concentrations of Pb results in the malfunction of the protective barrier formed by the protoplasmic membranes of root cells, and, as a result, Pb can be transported to xylem vessels by protoplast flow [20]. Studies have also pointed out that the roots of hyperaccumulators can uptake Pb through both the symplast and apoplast pathways [21,22]. Meanwhile, researchers have indicated that transporters can control the transportation of metal ions [23]. In addition to transporters, ion channels, such as calcium ion channels, can also be an access point for Pb to enter plant root cells [24,25]. Pb can also enter plants through non-selective cation channels, such as cyclic nucleotide-gated ion channels [18]. However, it is rarely reported that the cation transportation pathway in woody plants is involved in the uptake and transportation of Pb. Studies have shown that the non-hyperaccumulator plant Camellia sinensis can uptake Pb, but the uptake is not active [26]. Thus far, studies have not clearly elucidated the contribution of the symplast and apoplast pathways in facilitating the entry of lead ions into the xylem of woody plants.
Rhus chinensis Mill is a small deciduous tree with the properties of fast growth and strong environmental adaptability [27,28]. It is also a pioneer species and can grow in Pb/Zn mine tailing areas due to its good tolerance of various heavy metals [29]. Therefore, R. chinensis is a potential candidate for Pb phytoremediation. Our preliminary studies showed that R. chinensis plants can uptake a copious amount of Pb, and under hydroponic conditions the plants can also transfer a substantial amount of Pb to their aboveground parts [28]. However, it is unknown how Pb gains access to the roots of R. chinensis plants after it is adsorbed onto the cell walls in the roots. In this study, through controlled experiments, we aimed to determine whether active transportation exists in the process of Pb uptake in R. chinensis plants. In addition, the effects of La3+ on the uptake and transportation of Pb in R. chinensis plants were determined to ascertain whether the calcium ion channel in R. chinensis plants is involved in the uptake and transportation of Pb.

2. Materials and methods

2.1. Plant Materials and Growth Conditions

A preliminary test showed that there was no significant difference among different families in the capacity for Pb uptake and accumulation in R. chinensis from different regions. Therefore, the seeds were collected from the same plant of R. chinensis grown in Fuyang District Hangzhou City, Zhejiang Province. The propagation and culture of R. chinensis plants were performed according to the method reported by Shi et al. [28].

2.2. Experimental Method

The experiment was carried out in the greenhouse of the Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou, China. One-year-old plants of R. chinensis with similar growth states were selected and transferred into a container with a size of 45 cm × 35 cm × 15 cm (length × width × height). The plants were first cultured in water. After they adapted to the water culture conditions, the water was replaced with Knop’s solution. The hydroponic culture was performed at 30–38 °C under natural light with 60%–80% relative humidity and continuous aeration. During hydroponic culture, the pH value of the culture solution was adjusted to 5–6 using a HCl or NaOH solution. Subsequently, the pre-cultured plants were transferred into 250 mL Erlenmeyer flasks which were wrapped with tinfoil [8]. The following tests were carried out in an artificial climate chamber.

2.2.1. Time Course Experiment

A total of ten treatments (1, 1.5, 2, 3, 5, 7, 12, 24, 48, and 72 h) were set. The uptake solution contained 2 mmol L−1 MES-TRIS (pH 5.8) and 400 µmol L−1 Pb(NO)3. According to our previous study, under this concentration R. chinensis plants can grow well [28]. In the following tests, the uptake solution contained 2 mmol L–1 MES-TRIS (pH 5.8) and various concentrations of Pb(NO)3.

2.2.2. Investigation of the Concentration-Dependent Kinetics of Pb

Uptake solutions of eight concentrations (25, 50, 75, 100, 150, 200, 300, and 400 µmol L−1 Pb(NO)3) were prepared and used in the investigation.

2.2.3. Effect of Different Culture Medium on Pb Uptake and Transportation

The pre-cultured plants were transferred and cultured in 200 mL of uptake solution or hydroponic nutrient solution. The concentrations of solutions were 200 and 400 µmol L−1.

2.2.4. Effect of Metabolic Inhibitors on Pb Uptake and Transportation

Three treatments were used in this experiment, including 400 µmol L−1 Pb(NO)3 (control), 50 µmol L−1 2,4-dinitrophenol (DNP) plus 400 µmol L−1 Pb(NO)3, and 200 µmol L−1 carbonyl cyanide m-chlorophenylhydrazone (CCCP) plus 400 µmol L−1 Pb(NO)3.

2.2.5. Effect of Transpiration Inhibitors on Pb Uptake and Transportation

The uptake solution used in the culture contained 400 µmol L−1 Pb(NO)3. A solution of 2.0% transpiration inhibitor (87% paraffin base petroleum oil + 13% surfactants) was sprayed daily on the leaves of R. chinensis plants during culture. The plants in the control group were not sprayed with a transpiration inhibitor.

2.2.6. Effect of Low Temperature on Pb Uptake and Transportation

Low temperature (4 °C) and room temperature (25 °C) treatments were used in the experiment, and the uptake solution contained 400 µmol L−1 Pb(NO)3. For low-temperature treatment, the roots were pre-cooled on ice-cold pre-treatment solution for 30 min [16].

2.2.7. Effects of Ion Channel Inhibitors and Protein Synthesis Inhibitors on Pb Uptake and Transportation

Solutions used in the experiment included 400 µmol L−1 Pb(NO)3 (control), 50 µmol L−1 calcium channel inhibitor LaCl3 plus 400 µmol L−1 Pb(NO)3, and 50 µmol L−1 Protein synthesis inhibitor cycloheximide (CHD) plus 400 µmol L−1 Pb(NO)3.
In the above experiments, 18 one-year-old R. chinensis plants were used in each treatment, and each treatment had three replicates. One plant was planted in each flask. The plants were treated for 72 h and then harvested to determine the Pb concentration according to the method reported by Shi et al. [28].

2.3. Histochemical Staining of Pb in Roots

Seedlings were treated with 100 µmol L−1 Pb(NO)3 for 24 h. After the desorption by 20 mmol L−1 EDTA-Na2, five root pieces were used for histochemical staining. The modified dithizone method was used in root Pb staining. The dithizone solution was prepared according to the literature report of Wang et al. [8]. The roots were immersed in the solution for 1 h, and then rinsed with deionized water. ZEISS IMAGER A2 microscopy was used to obtain stained root images.

2.4. Statistical Analysis

Statistical software SPSS 19.0 was used for variance analysis to test the significance of differences with Fisher’s least significant difference (LSD) procedure. Data in figures and tables are presented as the mean ± standard error (figures) or standard deviation (tables).

3. Results

3.1. Time-Dependent Uptake of Pb in Different Organs

Generally, with the prolongation of treatment time, the Pb concentration in all organs of R. chinensis was significantly increased (Figure 1), and the Pb concentration did not reach saturation value. The whole kinetics were fitted with the Freundlich model (Figure 1). The whole process of roots can be divided into two stages: rapid uptake (0–3 h) and slower uptake (3–72 h), and the two stages can be described by a linear equation. Unlike the uptake process in roots, a rapid uptake of Pb in stems and leaves occurred within 7 h, followed by a relatively slower accumulation stage after 7 h.

3.2. Concentration-Dependent Kinetics of Lead Uptake

The concentration-dependent kinetics of Pb uptake by the organs of R. chinensis plants can be expressed using a smooth and unsaturated curve (Figure 2). The data obtained from the experiment were fitted with a modified Michaelis–Menten model. The equation of the model was:
Vc = Vmax[C] / (Km + [C]) + a[C]
where Vc is the uptake rate, Vmax is the maximum uptake rate, Km is a constant characterizing the relationship between plant cells and element uptake, and [C] is the substrate concentration. a is parameter characterizing the linear part of the uptake rate.
The rate of Pb uptake by the roots, stems, and leaves of R. chinensis plants increased with an increase in the concentration of Pb solution, showing a concentration-dependent effect. The results listed in Table 1 show that the R2 ranged between 0.882 and 0.998, indicating that the relationship between the uptake rate and the concentration of Pb solution fit the modified Michaelis–Menten kinetic model. Further analysis of the kinetic parameters showed that the order of the maximum uptake rate (Vmax) among the organs was root > stem > leaf. Vmax reflects the inherent potential of plant roots for uptake Pb, with a higher Vmax meaning a greater potential for Pb uptake. The results listed in Table 1 indicate that the roots had a certain potential for Pb uptake. Km reflects the carrier’s affinity for ions, and the lower the value, the stronger the carrier’s affinity. The data in Table 1 indicate that the Km for stems was significantly higher than that for other organs. The slopes of the linear part of the curves for roots, stems, and leaves were 0.0733, 0.0206, and 0.0242, respectively, indicating that the cell walls in the roots had an ability to bind Pb.

3.3. Effect of Different Culture Medium on Pb Uptake and Transportation

Rhus chinensis plants accumulated significantly more Pb from Pb uptake solutions (200 and 400 μmol L−1) than that from nutrient solution (p < 0.05). The Pb concentrations in the roots of the plants treated with nutrient solution were 39.1 and 50.7% of those treated with uptake solutions, respectively. The concentrations of Pb in the stems and leaves of the plants treated with uptake solutions were also significantly higher than that treated with nutrient solution, except for the leaves of the plants treated with 200 μmol·L−1 Pb(NO)3 (Figure 3).

3.4. Effect of Transpiration Inhibitors and Low Temperatures on Pb Uptake and Transportation

Rhus chinensis plants were harvested on the third day, and water depletion was measured by the weight difference method [30]. Compared to the control, the transpiration rate of R. chinensis was reduced by 38% ((p < 0.05) (Figure 4A). The Pb concentration in the roots of the plants sprayed with the transpiration inhibitor was 648.8 mg kg−1, which was only 5.2% lower than that of the control group (Figure 4B). The Pb concentrations in the stems and leaves also showed a similar phenomenon. The low-temperature treatment significantly reduced lead uptake and transportation (p < 0.05). The Pb concentration in the roots of the plants treated at low temperatures was 80.5% of that treated at room temperature. The Pb concentration in leaves was significantly reduced by low temperature, which was only 65.3 mg kg−1. However, there was no significant difference between room temperature and low temperature treatments in terms of the Pb concentration in the stems of the plants.

3.5. Effect of Metabolic Inhibitors on Pb Uptake and Transportation

Both metabolic inhibitors inhibited Pb uptake by the roots. DNP reduced the Pb concentration in the roots by 28.6% compared with the control (Figure 5). The Pb concentration in the roots of the plants treated with CCCP was 527.8 mg kg−1, which was significantly lower than that of the control (684.6 mg kg−1). However, there was no significant difference in the Pb concentration in the roots between the DNP and CCCP treatments. Meanwhile, the Pb concentrations in the stems and leaves of the plants treated with DNP and CCCP were also significantly lower than that of the control (p < 0.05). Compared with the control, CCCP and DNP treatments reduced the Pb concentration in stems by 29.4% and 32.1%, respectively. The Pb concentration in the leaves treated with DNP was only 108.7 mg kg−1, which was significantly lower than that treated with CCCP (p < 0.05).

3.6. Effect of Ion Channel Inhibitors and Protein Inhibitors on Lead Uptake

The addition of the calcium ion channel inhibitor LaCl3 reduced the Pb concentration in roots by 94.0 mg kg−1 compared with the control (Figure 6). The addition of the protein synthesis inhibitor CHD inhibited Pb uptake by roots and reduced the Pb concentration in roots by 10.8% compared with the control (Figure 6). Variance analysis showed that there was no significant difference in the Pb concentration in roots among the treatments. Similarly, the Pb concentrations in the stems and leaves of the plants treated with the inhibitors were significantly lower than those in the control, and the Pb concentrations in the stems and leaves of the plants treated with the protein synthesis inhibitor were the lowest (100.0 and 102.2 mg kg−1, respectively; p < 0.05).

3.7. Pb Localization in Roots

The presence of Pb in the root was observed as red to rufous complexes of Pb with dithizone. In the histochemical staining of roots, rufous spots were observed continually on root tips after a 24 h treatment with Pb (Figure 7), while these spots were not found in the roots of control seedling. Meanwhile, the Pb deposits were localized mainly at positions 600–800 µm from the root apex. With distance away from this site, the Pb deposits gradually decreased. The Pb deposits were negligible at the root cap. In addition, the Pb deposits also localized in the stele cylinder, albeit rarely.

4. Discussion

4.1. Characteristics of Pb Uptake in the Roots of R. chinensis

In general, plants take up heavy metals through the roots and translocate and enrich them to the aboveground parts. As a non-essential element in plants, Pb has been reported to enter the root system mainly through passive diffusion [8], so it is not difficult to explain the significant positive correlation between Pb concentration and treatment time in the root system of R. chinensis. Similar to Salix integra [8] and Triticum aestivum [31], the whole kinetics of Pb uptake were divided into two stages: rapid uptake and slower accumulation, and the two processes were fitted with a linear model. That uptake rate slowed gradually might be related to the damage to the cell membrane of root cell wall after Pb stress. In addition, the intercept was greater than zero, indicating that the desorption method used in this study did not completely remove the Pb bound on the apoplasm [31].
The value of slope k in the linear part of the concentration-dependent kinetic curve also indicated that the Pb uptake on the apoplast in the roots was not completely removed in the experiment. The saturable component of the kinetic curves suggests that the transport of Pb into the roots of R. chinensis plants were facilitated by carriers, which is consistent with the results of Wang et al. [31]. Additionally, in our study, both metabolic inhibitors and low temperature inhibited Pb uptake by the roots of R. chinensis plants, also indicating that Pb uptake by roots is partially regulated by related protein carriers on the cell plasma membrane [16]. The Vmax and Km value (14.83 and 19.44) of the concentration-dependent kinetic model indicated that the R. chinensis plants had a certain potential for uptake Pb. Since the uptake of elements by plants is affected by many factors [32], the Vmax/Km ratio can be considered to reflect the potential of R. chinensis plants to uptake Pb [33]. The Vmax/Km ratio of R. chinensis plants was 0.763, which also shows that they have a certain capacity to uptake Pb. In our study, both metabolic inhibitors significantly reduced the Pb concentration in the stems and leaves of R. chinensis plants, but most of the Pb remained in the root system. Therefore, we speculated that although Pb uptake by roots through the symplast pathway was regulated by the carrier, the barrier resulting from the strong compartmentalization of root cells and the lower loading capacity of the xylem might explain the low efficiency in translocating Pb to the aboveground parts of the plant [34].
In this study, most Pb deposits were found in the elongation zone and mature zone of R. chinensis root tips, which is in agreement with previous studies [8,35]. This might be due to the fact that the apical cells contain many meristematic tissues, thus more Pb deposits were observed at this site [36]. In addition, after 24 h, Pb deposits were found in the whole roots while a few deposits were appeared in the stele cylinder, suggesting that it was difficult for lead ions transferred from the cortex to the xylem [8]. This was one of the reasons why the rate of Pb accumulation in the stem and leaf decreased gradually after 24 h.

4.2. Pathways of Pb Uptake and Transportation in R. chinensis

Active uptake and passive uptake are two types of metal uptake in plants [17] Active uptake is the transmembrane transportation of metal ions, while passive uptake is a physical process [30]. In our study, the Pb concentration in the roots of the plants cultured in uptake solutions was significantly higher than that of the plants cultured in the nutrient solution treatment. This might be because the activity of lead ions in the uptake solution was higher than that in the nutrient solution, suggesting that Pb uptake by the roots of R. chinensis plants may not be completely passive [30]. After spraying a transpiration inhibitor, although the transpiration of plants was significantly reduced (38% reduction compared to the control), the Pb concentration in roots was not significantly different from the control, suggesting that there might be a process of active transportation in Pb uptake in R. chinensis plants. Low temperatures significantly inhibited Pb uptake by roots. A similar phenomenon was observed in S. alfredii [30]. Both metabolic inhibitors also significantly reduced the Pb concentration in the roots. Nonetheless, neither low temperature nor metabolic inhibitors completely inhibited active Pb uptake. These results show that both active and passive Pb uptake might exist in the roots of R. chinensis plants. Liu [37] reported that when the Pb concentration was low, hyperaccumulator ecotype S. alfredii plants mainly showed active uptake, while non-hyperaccumulator ecotype plants mainly showed passive uptake. While the Pb concentration was high, both of the ecotypes of S. alfredii plants mainly showed passive uptake. Similarly, our study concluded that both passive uptake and active Pb uptake exist in R. chinensis plants. However, Xu [26] reported that there was no active Pb uptake in C. sinensis. Liu [38] showed that both active and passive cadmium uptake exist in the Salix integra. Therefore, it can be speculated that both active and passive Pb uptake likely exists in non-hyperaccumulator plants.
Our study showed that, compared with the control, low temperatures significantly reduced the Pb concentration in the stems and leaves of R. chinensis plants, similar to Lu et al. [30], indicating that Pb transportation from roots to aboveground parts might have an energy-consuming process. Although the transpiration inhibitor decreased the Pb concentrations in stems and leaves compared with the control, the decrease was non-significant, indicating that the driving force resulting from transpiration was not the main role of Pb transportation to the aboveground parts. This result was similar to that of Liu et al. [39], but with a slight difference. Metabolic inhibitors significantly reduced the Pb concentration in the stems and leaves of R. chinensis plants, which also indicates that the transport of Pb into roots is an energy-requiring process [16]. DNP had a greater effect than CCCP, which may be due to the greater toxicity of DNP. These results indicate that there may be an energy-consuming active transportation process in R. chinensis plants by which Pb gains access to the roots. Since R. chinensis plants can uptake and accumulate Pb and have a certain ability to transport Pb to their aboveground parts, the role of the symplast pathway in related processes in this plant species needs to be studied further.

4.3. The Role of Ca Pathway in Pb Uptake and Translocation

To clarify whether Pb enters the root cells of R. chinensis plants through calcium ion channels, we investigated the effect of ion channel inhibitors on Pb uptake by the roots of R. chinensis plants. The addition of LaCl3 significantly reduced the uptake of lead ions by the roots. La3+ is a plasma membrane calcium channel blocker that can block the plasma membrane calcium ion channel to prevent extracellular calcium ions from entering cells [31] Therefore, Pb uptake by the roots of R. chinensis plants may be related to calcium ion channels. Similar phenomena have also been found in rice [40], tea trees [26], willows [38], and S. alfredii [41,42]. CHD can inhibit the synthesis and activity of some proteases in plants. In our study, CHD addition significantly reduced the Pb concentration in the roots of R. chinensis plants, indicating that Pb absorption might be related to the synthesis or activity of some proteases. Based on the results of the calcium treatments in this study, we believe that Pb uptake by R. chinensis plants is related to calcium ion channels, and is regulated by proteins on the membranes. However, treatment with a high concentration of calcium resulted in a higher Pb concentration in the roots of R. chinensis plants compared with the control, indicating that other cation channels might also be involved in Pb transportation in R. chinensis plants.

5. Conclusions

Pb uptake by the roots of R. chinensis plants was related to Pb activity in the solution. Transpiration inhibitors had no significant effect on Pb uptake or accumulation. Low temperatures and metabolic inhibitors (CCCP and DNP) significantly reduced the Pb concentration in the roots of R. chinensis plants. These results indicate that Pb uptake and transportation by R. chinensis plants are energy-requiring processes. The Pb concentration in different tissues of R. chinensis plants had a significant positive correlation with the Pb concentration of the solution, which could be expressed by a modified Michaelis–Menten equation. The parameters of the equation indicate that the carrier on the cell membranes might regulate Pb uptake. The addition of calcium ion channel inhibitors and protein synthesis inhibitors significantly reduced the Pb concentration in the roots of R. chinensis plants. These results indicate that Pb uptake by the roots of R. chinensis plants was related to calcium ion channels, but the existence of other cation channels in the transportation of Pb could not be ruled out.

Author Contributions

W.H.: Investigation, formal analysis, writing—original draft. S.W.: investigation. Y.W. and M.L.: writing—review & editing. X.S.: conceptualization, investigation, funding acquisition, project administration, writing—review & editing. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (No. 31870583).

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Time-course of Pb accumulation in different dry plant tissues of Rhus chinensis seedlings.
Figure 1. Time-course of Pb accumulation in different dry plant tissues of Rhus chinensis seedlings.
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Figure 2. Concentration-dependent Pb-Influx kinetics in different dry plant tissues of Rhus chinensis seedlings. Deconvolution of the overall kinetic curves into linear (dotted lined) and saturable components (black triangle) were derived from experimental data (black square).
Figure 2. Concentration-dependent Pb-Influx kinetics in different dry plant tissues of Rhus chinensis seedlings. Deconvolution of the overall kinetic curves into linear (dotted lined) and saturable components (black triangle) were derived from experimental data (black square).
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Figure 3. Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings grown in nutrition solution and uptake solution with different level Pb; Each value represents the mean of three (n = 3) replicates ± SE. Different letters indicate significant differences between data derived from the same bar (p < 0.05).
Figure 3. Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings grown in nutrition solution and uptake solution with different level Pb; Each value represents the mean of three (n = 3) replicates ± SE. Different letters indicate significant differences between data derived from the same bar (p < 0.05).
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Figure 4. Effect of 2.0% transpiration inhibitor on transpiration rate (A). Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings exposed to Pb, as affected by transpiration inhibltor and low temperature (B). Different letters indicate significant differences between data derived from the same bar (p < 0.05).
Figure 4. Effect of 2.0% transpiration inhibitor on transpiration rate (A). Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings exposed to Pb, as affected by transpiration inhibltor and low temperature (B). Different letters indicate significant differences between data derived from the same bar (p < 0.05).
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Figure 5. Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings exposed to Pb, as affected by CCCP and DNP. Different letters indicate significant differences between data derived from the same bar (p < 0.05).
Figure 5. Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings exposed to Pb, as affected by CCCP and DNP. Different letters indicate significant differences between data derived from the same bar (p < 0.05).
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Figure 6. Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings exposed to 400 μmol·L−1 Pb, as affected by LaCL3 and CHD. Different letters indicate significant differences between data derived from the same bar (p < 0.05).
Figure 6. Average Pb concentrations (mg kg−1) in dry plant tissues of Rhus chinensis seedlings exposed to 400 μmol·L−1 Pb, as affected by LaCL3 and CHD. Different letters indicate significant differences between data derived from the same bar (p < 0.05).
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Figure 7. Micrographs of roots from seedlings of Rhus chinensis exposed to 100 µmol L−1 Pb(NO)3, by using dithizone.
Figure 7. Micrographs of roots from seedlings of Rhus chinensis exposed to 100 µmol L−1 Pb(NO)3, by using dithizone.
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Table
Table 1. Parameters for uptake of Pb in different dry plant tissues of Rhus chinensis.
Table 1. Parameters for uptake of Pb in different dry plant tissues of Rhus chinensis.
Vmax (nmol g−1 h−1)KmVmax/KmaR2
Root14.8319.440.7630.07330.998
Stem7.182.230.0860.02060.882
Leaf3.0836.060.0850.02420.946
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He, W.; Wang, S.; Wang, Y.; Lu, M.; Shi, X. Pathways and Characteristics of Lead Uptake and Transportation in Rhus chinensis Mill. Forests 2023, 14, 90. https://doi.org/10.3390/f14010090

AMA Style

He W, Wang S, Wang Y, Lu M, Shi X. Pathways and Characteristics of Lead Uptake and Transportation in Rhus chinensis Mill. Forests. 2023; 14(1):90. https://doi.org/10.3390/f14010090

Chicago/Turabian Style

He, Wenxiang, Shufeng Wang, Yangdong Wang, Mengzhu Lu, and Xiang Shi. 2023. "Pathways and Characteristics of Lead Uptake and Transportation in Rhus chinensis Mill" Forests 14, no. 1: 90. https://doi.org/10.3390/f14010090

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