Open AccessArticle

The Effects of Localized Heating and Ethephon Application on Cambial Reactivation, Vessel Differentiation, and Resin Canal Development in Lacquer Tree, Toxicodendron vernicifluum, from Winter to Spring

Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan

Author to whom correspondence should be addressed.

Forests 2024, 15(11), 1977; https://doi.org/10.3390/f15111977

Submission received: 2 October 2024 / Revised: 2 November 2024 / Accepted: 5 November 2024 / Published: 8 November 2024

(This article belongs to the Section Wood Science and Forest Products)

Browse Figures

Versions Notes

Abstract

Resin canals serve as a natural feature with the function of a defense system against fungi, bacteria, and insects. Trees can form these canals in response to mechanical injury and ecological disturbance. Factors, such as plant hormones and temperature, influence cambial activity and cell differentiation. This study examined the effects of increased temperature and plant hormones on cambial reactivation, vessel formation, and resin canal formation using localized heating and the application of the ethylene generator ethephon to dormant stems of the Toxicodendron vernicifluum seedlings. Localized heating was achieved by wrapping an electric heating ribbon around dormant stems, while ethephon was applied to the bark surface. Treatment was initiated on 29 January 2021, including control, heating, ethephon, and a combination of heating and ethephon. Cambial reactivation and resin canal formation were monitored using light microscopy, and bud growth was recorded with a digital camera. Localized heating induced earlier phloem reactivation, cambial reactivation, and xylem differentiation, increasing the number of vessels. The application of exogenous ethylene delayed these processes. The combination of localized heating and exogenous ethylene application resulted in smaller vessels and larger resin canals. These results suggest that increased temperature plays a significant role in cambial reactivation and vessel formation in ring-porous hardwood and that ethylene affects vessel differentiation and resin canal development.

Keywords:

cambium; ethylene; localized heating; resin canal; Toxicodendron vernicifluum; vessel differentiation

1. Introduction

Wood is used as a sustainable raw material for the production of timber, furniture, pulp, paper, and fuel [1,2]. The biological process of wood formation plays a crucial role in mitigating climate change by fixing atmospheric carbon dioxide through photosynthesis and producing cell wall materials. Wood is produced by the meristematic tissue in the stem of trees, known as the cambium [3,4]. Therefore, the quantity and quality of wood are determined by the duration and rate of cambial cell division and the differentiation of cambial derivatives, including phloem and xylem cells. These processes involve cell elongation or expansion, cell wall thickening, the formation of modified cell wall structures, and cell death [2].

The cambium of trees in temperate and cool climate zone exhibits a seasonal periodicity of activity, which is controlled by both environmental and internal factors [5,6,7,8]. The timing of cambial reactivation from the late winter to early spring influences both the quantity and the quality of the wood produced [5,9]. The earlier reactivation of the cambium extends the growing season, resulting in the wider radial growth of trees. When the air temperature begins to rise from late winter to early spring, the dormant cambium becomes active under natural conditions. Artificially increasing the temperature of stems through localized heating during winter dormancy has been shown to induce earlier cambial reactivation in several conifers, a diffuse-porous hardwood, and a ring-porous hardwood [1,5,9,10]. Thus, temperature increases from late winter to early spring may directly trigger cambial reactivation in temperate trees. Cambial reactivation occurs when accumulated daily maximum temperatures exceed a certain threshold [1]. In a different study, Rossi et al. [7,11,12] reported that cambial activity and xylem differentiation started above a threshold value of mean daily temperature in conifers. Furthermore, the timing of cambial reactivation can be predicted by the calculation of the sum of temperatures that exceed a threshold [1,13].

They are also important for the production of chemicals and physiologically active substances. Toxicodendron vernicifluum, a lacquer tree widely distributed throughout East and Southeast Asia, is one of the most important species for wood biomass utilization. T. vernicifluum forms resin canals in the phloem and produces lacquer. In Japan, its resin is used as a coating, as an oil paint, and for making candles [14]. Due to its high demand, this species has recently been developed and cultivated extensively. Many researchers and farmers have attempted to develop high-yield resin-producing varieties. The resin canals in T. vernicifuum function as defense mechanisms against fungi, bacteria, and insects, and traumatic resin canals are produced in response to mechanical injuries and ecological disturbances, promoting lacquer production [15].

Several internal and external factors influence cambial activity and the differentiation of xylem and phloem cells. Plant hormones, particularly ethylene, play essential roles in regulating cell differentiation, growth, development, senescence, and responses to various disturbances or stresses [16,17,18,19,20]. Ethylene stimulates cambial cell division in Arabidopsis and hybrid aspen (Populus tremula × tremuloides) [21,22]. The application of the ethylene generator ethephon has been shown to induce the formation of traumatic gum canals without simultaneous wounding in Liquidambar formosana, while methyl jasmonate did not show this effect [23]. Furthermore, ethephon treatment during the active cambial season induces more gum canals in Cedrus libani [16]. However, it remains unclear how ethylene affects these tissues during winter when the cambium is dormant and during the transition as dormancy breaks in the early growing season.

This study aimed to analyze the factors controlling the timing of cambial reactivation, vessel differentiation, and the development of resin canals from winter to early spring in the deciduous ring-porous hardwood T. vernicifluum. Given its economic importance and viability in Japan, we selected the ring-porous deciduous hardwood T. vernicifluum.

2. Materials and Methods

2.1. Plant Materials

Fifty-one seedlings of Toxicodendron vernicifluum, which were approximately 1-year-old and healthy, were planted in 6.5 liter pots containing mixed black soil, humus, and pumice in 5, 3, and 2 parts, respectively, in the nursery of the Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo, Japan. These seedlings were used for the sequential observation of cambial reactivation and resin canal formation during treatment.

2.2. Treatment of Seedlings

The treatments were divided into four groups: control (no treatment), heat treatment, ethephon treatment, and a combination of heat and ethephon treatment.

Heat treatment: An electric heating wire was wrapped around the stem, starting 4 cm above the soil level and covering 5–6 cm of each seedling. An alternating current (100 V) was passed through the heating wire to warm the stem surface. The temperature between the outer bark and the heating wire was maintained at 20–22 °C using a thermostat (TC-1NP; As One Co., Osaka, Japan) and this was recorded using a data logger (Ondotori Jr. TR-52; T&D Co., Matsumoto, Japan) [14]. Ethephon treatment: 1 gram of 100 mM ethephon (Esrel 10, Ethephon liquid, Ishihara Bioscience, Tokyo, Japan) was administered in lanoline for each seedling. Ethephon was applied to the surface of the bark at 6–8 cm above the soil level. The combination of heat and ethephon treatment: The stems were treated with ethephon, as described above, and simultaneously wrapped with the stem using an electric heating wire, as described for the heat treatment method.

The treatments started on 29 January 2021, when the trees were dormant, and continued until the beginning of the spring season on 26 March 2021 to observe the effects of the treatments on the dormant cambium of T. vernicifluum.

2.3. Collection and Preparation of Samples for Microscopy

Samples were collected biweekly from 29 January 2021 to 26 March 2021. On each sampling date, the condition of the seedlings was recorded using a digital camera. Whole stems, as samples containing phloem, cambium, and xylem cells, were collected from 4 to 10 cm above the soil surface, where all treatments had been applied. Samples were fixed in a 5% solution of glutaraldehyde in 0.1 M phosphate buffer (pH 7.2) for approximately 24 h, and then washed with the same buffer.

To visualize the dimensions of the resin canal, transverse sections were cut using a sliding microtome (REM-710; Yamatokohki, Saitama, Japan) at a thickness of approximately 20 μm and stained with a 1% aqueous solution of safranin. To visualize the cambial reactivation, fixed samples were dehydrated using a graded ethanol series and we embedded them in epoxy resin. Transverse sections of approximately 2 μm thickness were cut using a rotary microtome (HM 340E; Carl Zeiss, Oberkochen, Germany), stained with a 1% of aqueous solution of toluidine blue, and observed under a light microscope (Axio Scope. A1; Carl Zeiss, Oberkochen, Germany).

2.4. Anatomical Measurements of Vessel Elements

The effects of the treatments on the anatomical features of vessel elements were evaluated based on their number, diameter, and area. Mature vessel elements from the current year were measured, with the xylem defined from the boundary of the previous year’s xylem to the cambial zone. Mature vessel elements were identified by thick secondary walls and blue-colored cell walls using toluidine blue staining. The number of vessel elements was counted, and the diameters of the vessel elements were measured as the average of the tangential and radial diameters, with only the largest diameter selected for the analysis. The areas of the vessel elements were measured using the total area of the vessel elements.

2.5. Anatomical Measurements of Resin Canals

The effects of the treatments on the resin canals were evaluated based on their number and diameter. Measurements were conducted in the area close to the cambial zone, within approximately 200 µm of the radial direction from the cambial zone. The diameters of the resin canals were measured using the average of the tangential and radial diameters.

2.6. Data Analysis

Quantitative analysis was used to evaluate the effects of the treatments on the characteristics of the resin canals (diameter and number) near the cambial zone and the characteristics of vessel elements (diameter and number) in the current year. The anatomical characteristics of the resin canals and vessels elements were measured using image analysis software ImageJ 1.53K (National Institutes of Health, MD, USA; [24]). One-way analysis of variance (ANOVA) was used to perform statistical analysis to determine statistically significant differences between treatments using the statistical software JASP 0.17 (University of Amsterdam, Amsterdam, the Netherlands). Values were considered statistically significant at p < 0.05.

3. Results

3.1. Temperature Profiles

The daily maximum, average, and minimum temperatures from January to March 2021 are shown in Figure 1. The daily temperature in the winter season, January–February 2021, reached −5.8 °C for the minimum temperature and 5.0 °C for the maximum temperature. During this season, the plants are in a dormant condition. At the beginning of the spring season, the temperature increased gradually, leading to plant reactivation. In March 2021, the minimum temperature reached 0.6 °C and the maximum temperature reached 22.9 °C.

3.2. Leaf Phenology

Figure 2 shows the leaf phenology of the seedlings of T. vernicifluum. On 29 January 2021, dormant buds were observed, as indicated by the unsprouted apical buds. The apical buds remained dormant on 12 February 2021 and 26 February 2021. On 12 March 2021, the apical buds began to swell in seedlings across all four treatments. By 26 March 2021, leaves had developed, and shoot extension began in all treatments.

3.3. Dormant Cambium

Before the start of the heat treatment, no division of fusiform and ray cambial cells was detected in the stem samples of cambium from T. vernicifluum that had been collected on 29 January 2021, indicating dormancy. The dormant cambium was located between the secondary phloem cells and thick-walled secondary xylem cells that had formed during the previous growing season. During dormancy, the cambium consisted of four or five radial layers of radially narrow and compactly arranged cells (Figure 3B).

3.4. Effects of Heating and Ethephon Treatment on Cambial Reactivation and Vessel Differentiation

The formation of the first new cell plates in the cambium from late winter to early spring is referred to as cambial reactivation [5]. In the control seedlings, the cambium was dormant on 12 February 2021 (Figure 4A). In contrast, the initial phloem cell division was observed in the heat-treated seedlings on the same date (Figure 4B, Table 1), with phloem cells located next to the cambial cells on the phloem side. The cambium remained dormant in ethephon-treated and heating-plus-ethephon-treated seedlings (Figure 4C,D).

Initial phloem cell division was detected in control seedlings on 26 February 2021 (Figure 5A, Table 1). By this date, cambial reactivation had already occurred in the stems of heat-treated seedlings, and the formation of the first earlywood vessels was observed (Figure 5B, Table 1). In ethephon-treated seedlings, initial phloem cell division was observed (Figure 5C, Table 1). Cambial reactivation was also detected in heat-plus-ethephon-treated seedlings on the same day (Figure 5D, Table 1).

On 12 March 2021, the first earlywood vessels were observed in control seedlings (Figure 6A, Table 1). Continuous cambial cell division and xylem differentiation occurred in heat-treated seedlings (Figure 6B). In ethephon-treated seedlings, only cambial cell division was observed (Figure 6C, Table 1). Cambial reactivation and the formation of the first earlywood vessels occurred simultaneously in heat-plus-ethephon-treated seedlings and the first earlywood vessels were formed (Figure 6D, Table 1).

By 26 March 2021, continuous cambial cell division and xylem differentiation were observed in all four treatments (Figure 7, Table 1). These results indicated that initial phloem cell division, cambial reactivation, and xylem differentiation occurred earlier in the stems of heat-treated seedlings compared to control seedlings. In contrast, the application of ethephon and heat-plus-ethephon treatments delayed these processes in T. vernicifluum seedlings.

3.5. Differences in Xylem Differentiation Among Treatments

Initial xylem cell differentiation in the hardwood species was observed by the appearance of the first vessel differentiation after cambial reactivation. In the control seedlings, initial vessel differentiation was observed 42 d after the start of the experiment, on 12 March 2021 (Figure 6A). In the heat-treated seedlings, initial vessel differentiation was observed 28 d after the start of the heat treatment, on 26 February 2021 (Figure 7B). In contrast, the initiation of xylem differentiation was delayed in ethephon-treated seedlings, initiating 56 d after the start of the experiment, on 26 March 2021 (Figure 7C). In the heat-plus-ethephon-treated seedlings, xylem differentiation was initiated 42 d after the start of the experiment, on 12 March 2021 (Figure 6D). These results indicate that localized heating induces xylem differentiation 14 d earlier in heated stems than in control stems under natural conditions. However, xylem differentiation in heat-plus-ethephon-treated seedlings was delayed by 14 d compared to that in the seedlings treated with heating only.

To understand the effects of the treatments on xylem differentiation, we observed the stems of T. vernicifluum seedlings collected 56 d after the start of the experiment, on 26 March 2021.

There were no significant differences in the width of the current year’s xylem among treatments (p > 0.05; Figure 8A). The width of the current year’s xylem (±s.d.) was 81.6 ± 4.9 µm in the control, 299.3 ± 96.2 µm in heat treatment, 78.8 ± 12.8 µm in the ethephon treatment, and 62.9 ± 47.6 µm in the heat-plus-ethephon treatment.

The number of vessels in the current year’s xylem differed significantly between the treatments (p < 0.01; Figure 8B). The number of vessels (±s.d.) was 4.7 ± 3.1 in the control, 25.0 ± 11.0 in heat treatment group, 2.7 ± 0.6 in the ethephon treatment group, and 5.0 ± 5.6 in the heat-plus-ethephon-treated group. Heated seedlings had significantly more vessels than the control, ethephon-treated, and heat-plus-ethephon-treated seedlings. There were no significant differences among the control, ethephon-treated, and heat-plus-ethephon-treated seedlings.

The diameter of vessels in the current year’s xylem differed significantly among the treatments (p < 0.05; Figure 8C). The vessel diameter (±s.d.) was 50.8 ± 24.9 µm in the control, 36.2 ± 5.2 µm in the heat treatment group, 48.4 ± 4.0 µm in the ethephon treatment group, and 13.4 ± 11.9 µm in the heat-plus-ethephon treatment group. Heat-plus-ethephon-treated seedlings had significantly smaller vessel diameters than control, heated, and ethephon-treated seedlings. There were no significant differences among the control, heated, and ethephon-treated seedlings.

To further clarify the effects of treatment on vessel characteristics, the areas of vessels that were formed in the xylem during the current year were calculated. The area of vessels in the current year’s xylem differed significantly among treatments (p < 0.05; Figure 8D). The vessel area (±s.d.) was 7552.2 ± 3228.0 µm² in the control group, 27,687.0 ± 14,863.3 µm² in the heat treatment group, 4932.6 ± 1120.9 µm² in the ethephon treatment group, and 1506.2 ± 1436.6 µm² in heat-plus-ethephon treatment group. Heat-plus-ethephon-treated seedlings had significantly smaller vessel areas than control, heated, and ethephon-treated seedlings. There were no significant differences between the control, heated, and ethephon-treated seedlings.

3.6. Effects of Localized Heating and Ethylene Treatment on Resin Canal Development

In T. vernicifluum, resin canals are formed by secretory cells filled with brown-colored lacquer and covered by sheath cells [25]. On 29 January 2021, before treatment, new resin canals were observed in the secondary phloem, while the cambium was dormant (Figure 3A).

To better understand the effect of treatments on resin canal formation, we measured the diameter and number of resin canals near the cambium in samples collected 56 d after treatment, on 26 March 2021 (Figure 9). There were no significant differences in the number of resin canals between the treatments (p > 0.05; Figure 10A). The number of resin canals (±s.d.) was 25.7 ± 5.5 in the control, 27.0 ± 6.1 in the heat treatment group, 36.7 ± 6.7 in the ethephon treatment group, and 35.0 ± 4.0 in the heat-plus-ethephon treatment group. The diameters of the resin canals differed significantly among the treatments (p < 0.05; Figure 10B). The resin canal diameter (±s.d.) was 47.5 ± 1.0 µm in the control group, 49.0 ± 1.1 µm in the heat treatment group, 48.1 ± 7.2 µm in the ethephon treatment group, and 58.5 ± 3.6 µm in the heat-plus-ethephon treatment group. Heat-plus-ethephon-treated seedlings had significantly larger resin canals than control seedlings. There were no significant differences among control, heated, and ethephon-treated seedlings.

4. Discussion

In the present study, we found that localized heating and exogenous ethylene application influenced wood formation in T. vernicifluum in various ways. Localized heating induced earlier cambial reactivation and xylem differentiation and increased the number of vessels. Conversely, exogenous ethylene application delayed phloem cell division, cambial reactivation, and xylem differentiation. Furthermore, the combination of localized heating and exogenous ethylene application resulted in the development of larger resin canals.

We observed that localized heating induced earlier phloem cell division than control treatment; however, when the ethephon was applied in combination with heating, phloem cell division was delayed. Similarly, Begum et al. [5] reported that localized heating could induce phloem cell division in the dormant stems of hybrid poplars. This observation suggests that ethylene, produced by the application of ethephon, may play a role in the process of the onset of phloem cell division in the early growing season.

Localized heating also influenced the timing of xylem differentiation in T. vernicifluum. In the heat-treated seedlings, the initial differentiation of the vessels occurred 28 d after treatment, which was 14 d earlier than in the control seedlings. In the control seedlings, xylem differentiation occurred 42 d after treatment, on 12 March 2021. Similarly, Begum et al. [5] and Kudo et al. [10] reported that localized heating induced earlier xylem differentiation in hybrid poplars and Quercus serrata. Our results support the hypothesis that temperature plays a crucial role in determining the timing of cambial reactivation and xylem differentiation.

Ethylene is a plant growth regulator that modulates cambial activity and xylem differentiation. Eklund and Tiltu [26] demonstrated that the application of exogenous ethylene stimulated cambial growth in Picea abies “virgata”. Additionally, Felten et al. [27] found that exogenous ethylene application to hybrid aspen (Populus tremula × tremuloides) induced auxin biosynthesis, leading to enhanced cambial activity. Furthermore, Pesquet and Tuominen [28] showed that ethylene stimulates tracheary element differentiation in Zinnia elegans in vitro systems via biochemical, molecular biological, and pharmacological experiments. However, Pramod et al. [29] reported that a high concentration of ethephon inhibits cambial cell division and xylem differentiation, while a low concentration induces cambial cell division in Leucaena leucocephala. Our study indicates that ethephon application inhibits initial vessel differentiation in T. vernicifluum seedlings. Compared to control seedlings, ethephon application induced a delay in the initial vessel differentiation. Moreover, initial vessel differentiation in the seedlings of T. vernicifluum treated with both heating and ethephon showed a delay compared to seedlings treated with heating alone. Our results indicate that a high concentration of ethylene may inhibit vessel differentiation.

Cambial reactivation and initial vessel differentiation occurred in the heat-treated seedlings of T. vernicifluum, while the apical buds were still dormant. Similarly, Begum et al. [5] and Kudo et al. [10] demonstrated that bud growth is not essential for cambial reactivation and initial vessel differentiation in the hybrid poplar and Quercus serrata. Our findings support the hypothesis that bud growth is not necessary for cambial reactivation or initial vessel differentiation in T. vernicifluum.

Shortly after cambial reactivation, cell differentiation began in the xylem. In this study, we investigated the effects of ethephon application on xylem differentiation in T. vernicifluum. Ethephon application inhibited the initiation of xylem differentiation, as shown in Figure 6. In ethephon-treated seedlings, xylem differentiation started 2 weeks later than in the control seedlings. Aloni et al. [30] reported that the application of 1% and 5% (w/w) ethephon decreased the vessel diameter in Lycopersicon esculentum. However, in our study, the diameter of the vessels in ethephon-treated seedlings was not significantly different from that of the control seedlings. It is possible that the concentration of ethephon applied in this study was not high enough to reduce vessel diameter in T. vernicifluum during early spring.

In this study, we observed the effects of combining heat and ethephon treatments on vessel differentiation in T. vernicifluum. There was no difference in the timing of vessel differentiation between the control and ethephon-treated seedlings. However, the timing of vessel differentiation in the heat-plus-ethephon-treated seedlings was earlier than that seen in the ethephon-treated seedlings, but later than that seen in the heat-treated seedlings. The combination of heat and ethephon had varied effects on the timing of vessel differentiation. The number of vessels was not significantly different among the control, ethephon, and heat-plus-ethephon-treated seedlings. In contrast, the number of vessels in the heat-plus-ethephon-treated seedlings was lower than that in the heat-treated seedlings. This suggests that the heating effect is suppressed in the presence of ethylene. Additionally, the diameters and areas of the vessels were significantly smaller in heat-plus-ethephon-treated seedlings than in the control, heat, and ethephon treatments alone. The combination of heat and ethephon treatment inhibited the enlargement of the vessel elements. Ethylene has been reported to reduce vessel size during the active growing season [30]. In our study, no significant differences were observed following the application of ethephon to dormant seedlings alone. However, the combination of heating and ethephon treatment significantly reduced the number, diameter, and area of vessels. This result indicates that heat treatment may have altered the ethylene sensitivity of differentiating cells, with ethylene strongly affecting vessel differentiation. Furthermore, heat treatment may have enhanced the effect of ethylene due to increased ethylene diffusion at higher temperatures.

The resin canals of T. vernicifluum were easily found in the secondary phloem. Zhao and Hu [25] reported that the resin canal structure in T. vernicifluum was formed by secretory cells filled with brown-colored lacquer and covered by sheath cells. One of the factors that can increase the number of resin canals in hardwood species is the plant hormone ethylene.

In this study, we examined the effects of ethylene in winter on dormant T. vernicifluum seedling stems with localized heating. The number of resin canals did not differ significantly between the treatments. In contrast, the diameters of the resin canals were significantly increased by the combination of heat and ethephon treatments. Zheng et al. [23] reported that the application of ethylene to Liquidambar formosana during the active growing season induced more resin canals with larger diameters than during other seasons. Our results suggest that heat treatment may alter the ethylene sensitivity of resin-producing cells, leading to the enlargement of resin canals. Additionally, heat treatment may have enhanced the effect of ethylene due to increased ethylene diffusion at higher temperatures.

5. Conclusions

We found that the localized heating of dormant stems of T. vernicifluum induced earlier phloem cell division, cambial reactivation, and xylem differentiation. Our results indicate that an increase in temperature plays a crucial role in cambial reactivation and xylem differentiation in the ring-porous hardwood T. vernicifluum, which is similar to the findings about Quercus serrata [10]. Additionally, the combination of localized heating and exogenous ethylene application to dormant stems of T. vernicifluum inhibited cambial reactivation and vessel differentiation, and also enlarged resin canals. These observations suggest that ethylene significantly affects vessel differentiation and resin canal development.

Author Contributions

Conceptualization, N.P.T., M.H.R., S.N. and R.F.; methodology, N.P.T., M.H.R., S.N. and R.F.; formal analysis, N.P.T.; writing—original draft preparation, N.P.T.; writing—review and editing, M.H.R., S.N. and R.F.; supervision, R.F. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (grant numbers JP21H02253, JP23H02273, JP23K26966, JP24K01822 and JP26242017).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Acknowledgments

The authors thank Yusuke Nakamura, Etsushi Iizuka, Junya Mori and Yoko Nozawa (Faculty of Agriculture, Tokyo University of Agriculture and Technology) for their assistance in the plant and experiment preparation. We are very grateful to the reviewers and editor for their constructive comments and suggestions.

Conflicts of Interest

The authors declare no conflicts of interest.

References

Begum, S.; Kudo, K.; Rahman, M.H.; Nakaba, S.; Yamagishi, Y.; Nabeshima, E.; Nugroho, W.D.; Oribe, Y.; Kitin, P.; Jin, H.O.; et al. Climate change and the regulation of wood formation in trees by temperature. Trees 2018, 32, 3–15. [Google Scholar] [CrossRef]
Fromm, J. Xylem development in tress: From cambial division to mature wood cells. In Cellular Aspects of Wood Formation. Plant Cell Monographs 20; Fromm, J., Ed.; Springer: Berlin/Heidelberg, Germany, 2013; pp. 3–39. [Google Scholar]
Catteson, A.M. Cambial ultrastructure and biochemistry: Changes in relation to vascular tissue differentiation and the seasonal cycle. Int. J. Plant Sci. 1994, 155, 251–261. [Google Scholar] [CrossRef]
Larson, P.R. The Vascular Cambium: Development and Structure; Springer: Berlin/Heidelberg, Germany; New York, NY, USA, 1994. [Google Scholar]
Begum, S.; Nakaba, S.; Oribe, Y.; Kubo, T.; Funada, R. Induction of cambial reactivation by localized heating in a deciduous hardwood hybrid poplar (Populus sieboldii × P. grandidentata). Ann. Bot. 2007, 100, 439–447. [Google Scholar] [CrossRef] [PubMed]
Denne, M.P.; Dodd, R.S. The environmental control of xylem differentiation. In Xylem Cell Development; Barnett, J.R., Ed.; Castle House: Tunbridge Wells, UK, 1981; pp. 236–255. [Google Scholar]
Rossi, S.; Morin, H.; Deslauriers, A. Causes and correlations in cambium phenology: Towards an integrated framework of xylogenesis. J. Exp. Bot. 2012, 63, 2117–2126. [Google Scholar] [CrossRef]
Bhalerao, R.P.; Fischer, U. Environmental and hormonal control of cambial stem cell dynamics. J. Exp. Bot. 2016, 68, 79–87. [Google Scholar] [CrossRef]
Gričar, J.; Zupančič, M.; Čufar, K.; Koch, G.; Schmitt, U.; Oven, P. Effect of local heating and cooling on cambial activity and cell differentiation in the stem of Norway spruce (Picea abies). Ann. Bot. 2006, 97, 943–951. [Google Scholar] [CrossRef]
Kudo, K.; Nabeshima, E.; Begum, S.; Yamagishi, Y.; Nakaba, S.; Oribe, Y.; Yasue, K.; Funada, R. The effects of localized heating and disbudding on cambial reactivation and formation of earlywood vessels in seedlings of the deciduous ring-porous hardwood, Quercus serrata. Ann. Bot. 2014, 113, 1021–1027. [Google Scholar] [CrossRef]
Rossi, S.; Deslauriers, A.; Anfodillo, T. Evidence of threshold temperatures for xylogenesis in conifers at high altitudes. Oecologia 2007, 152, 1–12. [Google Scholar] [CrossRef] [PubMed]
Rossi, S.; Deslauriers, A.; Gričar, J.; Seo, J.W.; Rathgeber, C.B.K.; Anfodillo, T.; Morin, H.; Levanic, T.; Oven, P.; Jalkanen, R. Critical temperatures for xylogenesis in conifers of cold climates. Global Ecol. Biol. 2008, 17, 696–707. [Google Scholar] [CrossRef]
Seo, J.W.; Eckstein, D.; Jalkanen, R.; Rickebusch, S.; Schmitt, U. Estimating the onset of cambial activity in scots pine in northern Finland by means of the heat-sum approach. Tree Physiol. 2008, 28, 105–112. [Google Scholar] [CrossRef]
Noshiro, S.; Suzuki, M.; Sasaki, Y. Importance of Rhus verniciflua Stokes (lacquer tree) in prehistoric periods in Japan, deduced from identification of its fossil woods. Veg. His. Archaeobot. 2007, 16, 405–411. [Google Scholar] [CrossRef]
Funada, R.; Hosaka, M.; Yamagishi, Y.; Tsukada, K.; Rahman, M.H.; Tabata, M.; Nakaba, S. Anatomical analysis of bark structure of Toxicodendron vernicifluum with different amounts of lacquer production. J. Jpn. Forest Soc. 2019, 101, 305–310, (In Japanese with English Summary). [Google Scholar] [CrossRef]
Fahn, A.; Werker, E.; Ben-Tzur, P. Seasonal effects of wounding and growth substances on development of traumatic resin ducts in Cedrus libani. New Phytol. 1979, 82, 537–544. [Google Scholar] [CrossRef]
Yamamoto, F.; Iwanaga, F.; Al-Busaidi, A.; Yamanaka, N. Roles of ethylene, jasmonic acid, and salicylic acid and their interactions in frankincense resin production in Boswellia sacra Flueck. trees. Sci. Rep. 2020, 10, 16760. [Google Scholar] [CrossRef] [PubMed]
Aloni, R. Phytohormonal mechanisms that control wood quality formation in young and mature trees. In The Compromised Wood Workshop 2007; Entwistle, K., Harris, P., Walker, J., Eds.; The Wood Technology Research Centre, University of Canterbury: Christchurch, New Zealand, 2007; pp. 1–22. [Google Scholar]
Aloni, R. Role of hormones in controlling vascular differentiation and the mechanism of lateral root initiation. Planta 2013, 238, 819–830. [Google Scholar] [CrossRef]
Buttò, V.; Deslauriers, A.; Rossi, S.; Rozenberg, P.; Shishov, V.; Morin, H. The role of plant hormones in tree-ring formation. Trees 2020, 34, 315–335. [Google Scholar] [CrossRef]
Yang, S.; Wang, S.; Li, S.; Du, Q.; Qi, L.; Wang, W.; Chen, J.; Wang, H. Activation of ACS7 in Arabidopsis affects vascular development and demonstrated a link between ethylene synthesis and cambial activity. J. Exp. Bot. 2020, 71, 7160–7170. [Google Scholar] [CrossRef]
Love, J.; Björklund, S.; Vahala, J.; Hertzberg, M.; Kangasjärvi, J.; Sundberg, B. Ethylene is an endogenous stimulator of cell division in the cambial meristem of Populus. Proc. Natl. Acad. Sci. USA 2009, 106, 5984–5989. [Google Scholar] [CrossRef]
Zheng, Y.; Pan, B.; Itoh, T. Chemical induction of traumatic gum ducts in Chinese sweetgum, Liquidambar formosana. IAWA J. 2015, 36, 58–68. [Google Scholar] [CrossRef]
Schneider, C.A.; Rasband, W.S.; Eliceiri, K.W. NIH Image to ImageJ: 25 years of image analysis. Nat. Methods 2012, 9, 671–675. [Google Scholar] [CrossRef]
Zhao, M.; Hu, C. An ultrastructural study of the development of resin canals and lacquer secretion in Toxicodendron vernicifluum (Stokes) F.A.Barkley. S. Afr. J. Bot. 2018, 116, 61–66. [Google Scholar] [CrossRef]
Eklund, L.; Tiltu, A. Cambial activity in ‘normal’ spruce Picea abies Karst (L.) and snake spruce Picea abies (L.) Karst f. virgata (Jacq.) Rehd in response to ethylene. J. Exp. Bot. 1999, 50, 1489–1493. [Google Scholar] [CrossRef]
Felten, J.; Vahala, J.; Love, J.; Gorzsás, A.; Rüggeberg, M.; Delhomme, N.; Leśniewska, J.; Kangasjärvi, J.; Hvidsten, T.R.; Mellerowicz, E.J.; et al. Ethylene signaling induces gelatinous layers with typical features of tension wood in hybrid aspen. New Phytol. 2018, 218, 999–1014. [Google Scholar] [CrossRef]
Pesquet, E.; Tuominen, H. Ethylene stimulates tracheary element differentiation in Zinnia elegans cell cultures. New Phytol. 2011, 190, 138–149. [Google Scholar] [CrossRef]
Pramod, S.; Patel, P.B.; Rao, K.S. Influence of exogenous ethylene on cambial activity, xylogenesis and ray initiation in young shoots of Leucaena leucocephala (lam.) de Wit. Flora Morphol. Distrib. Funct. Ecol. Plants 2013, 208, 549–555. [Google Scholar] [CrossRef]
Aloni, R.; Wolf, A.; Feigenbaum, P.; Avni, A.; Klee, H.J. The never ripe mutant provides evidence that tumor-induced ethylene controls the morphogenesis of Agrobacterium tumefaciens-induced crown galls on tomato stems. Plant Physiol. 1998, 117, 841–849. [Google Scholar] [CrossRef]

Figure 1. Meteorological data showing the maximum, average, and minimum daily air temperatures at the experimental site in Fuchu, Tokyo, Japan, from January to March 2021. Dotted line ① indicates the timing of the initial phloem cell division in heat-treated seedlings. Dotted line ② indicates the timing of the initial phloem cell division in control and ethephon-treated seedlings and the timing of the cambial reactivation in heat-plus-ethephon-treated seedlings.

Figure 2. Apical bud conditions of T. vernicifluum seedlings 14 days, 28 days, 42 days, and 56 days after treatments. Dormant apical buds were observed until 26 February 2021 in all treatments. Bud swelling was observed on 12 March 2021, and leaf development and the start of shoot extension began on 26 March 2021 in all treatments.

Figure 3. Light micrographs showing transverse sections of T. vernicifluum on 29 January 2021, with (A) low magnification and (B) high magnification. White arrows indicate resin canals in the phloem area. Ph: phloem; Ca: cambial zone; Xy: xylem. Scale: (A) 100 μm, (B) 25 μm.

Figure 4. Light micrographs showing the cambial zone in transverse sections of (A) control seedlings, (B) heat-treated seedlings, (C) ethephon-treated seedlings, and (D) heat-plus-ethephon-treated seedlings of T. vernicifluum on 12 February 2021. Dormant cambial cells were observed in all treatments; however, initial phloem cell division was detected in the heat-treated seedling, indicated by the yellow arrow. Ph: phloem; Ca: cambial zone; Xy: xylem; Rc: resin canal. Scale: 50 μm.

Figure 5. Light micrographs showing cambial activity in transverse sections of (A) control seedlings, (B) heat-treated seedlings, (C) ethephon-treated seedlings, and (D) heat-plus-ethephon-treated seedlings of T. vernicifluum on 26 February2021. Cell division was observed in the phloem and cambium in all treatments. Differentiating vessel elements were only detected in the heat-treated seedling. Yellow arrows indicate cell division in the phloem and cambium. A red arrow indicates a differentiating vessel element. Ph: phloem; Ca: cambial zone; Xy: xylem. Scale: 50 μm.

Figure 6. Light micrographs showing cambial activity in transverse sections of (A) control seedlings, (B) heat-treated seedlings, (C) ethephon-treated seedlings, and (D) heat-plus-ethephon-treated seedlings of T. vernicifluum on 12 March 2021. Cambial cell division was observed in all treatments. Differentiating vessel elements were detected in the control, heat-treated, and heat-plus-ethephon-treated seedlings. Yellow arrows indicate cambial cell division. Red arrows indicate differentiating vessel elements. Ph: phloem; Ca: cambial zone; Xy: xylem; Rc: resin canal. Scale: 50 μm.

Figure 7. Light micrographs showing cambial activity in transverse sections of (A) control seedlings, (B) heat-treated seedlings, (C) ethephon-treated seedlings, and (D) heat-plus-ethephon-treated seedlings of T. vernicifluum on 26 March 2021. Cambial cell division and differentiating vessel elements were observed in all treatments. Yellow arrows indicate cambial cell division. Red arrows indicate differentiating vessel elements. Ph: phloem; Ca: cambial zone; Xy: xylem. Scale: 50 μm.

Figure 8. Graphs showing (A) xylem width, (B) number of vessels, (C) diameter of vessels, and (D) area of vessels in the current year’s xylem of T. vernicifluum on 26 March 2021 (n = 3). Columns and bars show mean values ± s.d. Means with the different letters are significantly different at p < 0.05 (one-way ANOVA, Tukey’s HSD test).

Figure 9. Light micrographs showing transverse sections of (A) control seedlings, (B) heat-treated seedlings, (C) ethephon-treated seedlings, and (D) heat-plus-ethephon-treated seedlings of T. vernicifluum on 26 March 2021. Ph: phloem; Ca: cambial zone; Rc: resin canal, NXy: current year’s xylem. Scale: 100 μm.

Figure 10. Graph showing (A) number and (B) diameter of the resin canals of T. vernicifluum on 26 March 2021 (n = 3). Columns and bars show mean values ± s.d. Means with the different letters are significantly different at p < 0.05 (one-way ANOVA, Tukey’s HSD test).

Table 1. The timing of the division of phloem cells, cambial reactivation, and xylem differentiation in control, heat-treated, ethephon-treated, and heat-plus-ethephon-treated seedlings of Toxicodendron vernicifluum from 29 January 2021 to 26 March 2021.

Date	Control Seedlings	Heat-Treated Seedlings	Ethephon-Treated Seedlings	Heat-Plus-Ethephon- Treated Seedlings
12 February (14d after treatments)		Phloem cell division
26 February (28d after treatments)	Phloem cell division	Initiation of differentiation into vessel elements	Phloem cell division	Cambial reactivation
12 March (42d after treatments)	Initiation of differentiation into vessel elements		Cambial reactivation	Initiation of differentiation into vessel elements
26 March (56d after treatments)			Initiation of differentiation into vessel elements

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Share and Cite

MDPI and ACS Style

Tiyasa, N.P.; Rahman, M.H.; Nakaba, S.; Funada, R. The Effects of Localized Heating and Ethephon Application on Cambial Reactivation, Vessel Differentiation, and Resin Canal Development in Lacquer Tree, Toxicodendron vernicifluum, from Winter to Spring. Forests 2024, 15, 1977. https://doi.org/10.3390/f15111977

AMA Style

Tiyasa NP, Rahman MH, Nakaba S, Funada R. The Effects of Localized Heating and Ethephon Application on Cambial Reactivation, Vessel Differentiation, and Resin Canal Development in Lacquer Tree, Toxicodendron vernicifluum, from Winter to Spring. Forests. 2024; 15(11):1977. https://doi.org/10.3390/f15111977

Chicago/Turabian Style

Tiyasa, Novena Puteri, Md Hasnat Rahman, Satoshi Nakaba, and Ryo Funada. 2024. "The Effects of Localized Heating and Ethephon Application on Cambial Reactivation, Vessel Differentiation, and Resin Canal Development in Lacquer Tree, Toxicodendron vernicifluum, from Winter to Spring" Forests 15, no. 11: 1977. https://doi.org/10.3390/f15111977

APA Style

Tiyasa, N. P., Rahman, M. H., Nakaba, S., & Funada, R. (2024). The Effects of Localized Heating and Ethephon Application on Cambial Reactivation, Vessel Differentiation, and Resin Canal Development in Lacquer Tree, Toxicodendron vernicifluum, from Winter to Spring. Forests, 15(11), 1977. https://doi.org/10.3390/f15111977

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Menu