Differences in the Adaptive Development of Suberin in the Tobacco Root Endothelial Layer under Different Potassium Levels

doi:10.11983/CBB24191

Abstract

Abstract: INTRODUCTION: Apoplastic barriers differentiated from the root endoderm play important roles in plant stress resistance and nutrient uptake, and the development of suberin lamellae has become a popular research topic in recent years.
RATIONALE: Hydroponic experiments with potassium concentrations ranging from 0.1 to 4.0 mmol∙L^-1 were conducted, using the cultivated tobacco variety Zhongyan 100 as the experimental material, to explore the effects of different potassium supplies on the endodermal suberization and its physiological and molecular mechanisms.
RESULTS: Low potassium (0.1 mmol∙L^-1) stress significantly enhanced the endodermal suberization: the absolute length of the fully suberized region ranged from 0-2 cm in the control to 4-6 cm, and the relative proportion increased from 0-15.0% to 33.2%-44.3%. These findings indicate that suberization is one of the key morphological adaptation mechanisms in tobacco under low potassium stress. Phenotypic analysis revealed that under low potassium stress, root elongation increased while plant biomass decreased, and the potassium ion content and accumulation in both the aboveground and root parts decreased. Additionally, the flow rate and potassium ion concentration in the xylem sap decreased, indicating reduced transport efficiency. Endogenous hormone analysis revealed that low potassium stress increased the abscisic acid (ABA) content in roots while suppressing ethylene and methyl jasmonate levels, forming a specific hormonal regulatory network. The transcriptome data further supported the molecular basis of suberization development, showing significant upregulation of genes related to suberin synthesis and transport (e.g., CYP86, GPAT, and ABCG) and their upstream positive regulatory factors (MYB36, MYB41, MYB92, and MYB93).
CONCLUSION: This study is the first to reveal that low potassium stress regulates the suberization developmental program of tobacco roots through ABA-mediated hormonal signaling reprogramming, providing a novel perspective for understanding the adaptation mechanisms of plants to potassium stress.

Fluorescence imaging of transverse sections of the endodermis development in tobacco roots under three potassium concentrations (bars=130 μm)

Key words: suberization, potassium, root endodermis, hormone

Yunxiang Xu, Liwen Zhang, Peng Wang, Yingchen Gu, Madan Lal Kolhi, Biao Zhang, Yingying Zhu, Haiwei Liu. Differences in the Adaptive Development of Suberin in the Tobacco Root Endothelial Layer under Different Potassium Levels[J]. Chinese Bulletin of Botany, 2025, 60(6): 914-930.

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URL: https://www.chinbullbotany.com/EN/10.11983/CBB24191

https://www.chinbullbotany.com/EN/Y2025/V60/I6/914

Figures/Tables 11

Table 1 Preparation methods for the reagents required for suberization fluorescence staining of tobacco root

Reagent	Configuration method
0.01% (w/v) FY 088	Dissolve 0.01 g of FY 088 powder in 100 mL of distilled water, mix well, and heat to 70°C before using
0.05% (w/v) toluidine Blue O	Dissolve 0.05 g of toluidine blue O powder in 100 mL of distilled water, mix well and store away from light
4% (w/v) agar	Dissolve 4 g of agar powder in 100 mL of distilled water, mix well and heat in a microwave oven over medium heat for 3 min
50% (v/v) glycerol-ethanol	Mix absolute ethanol 1:1 with glycerol well

Table 2 Differences in tobacco biomass and the root/shoot ratio under different concentrations of potassium

Treatments (mmol∙L^-1 K⁺)	Shoot fresh weight (g)	Root fresh weight (g)	Shoot dry weight (g)	Root dry weight (g)	Root-shoot ratio
0.1	7.32±0.96 c	0.70±0.08 b	0.30±0.04 b	0.06±0 b	0.19±0.02 a
0.5	10.51±2.25 bc	0.84±0.08 ab	0.47±0.09 a	0.06±0 b	0.14±0.03 bc
1.0	12.33±2.43 b	0.93±0.07 ab	0.53±0.10 a	0.06±0.01 ab	0.12±0.03 c
2.0	13.24±2.51 ab	1.09±0.41 ab	0.54±0.13 a	0.08±0.02 a	0.16±0.01 b
4.0	16.03±2.76 a	1.03±0.26 a	0.60±0.10 a	0.08±0.02 a	0.14±0.01 bc

Figure 1 Growth and root morphological development of tobacco plants under different potassium concentrations (A) Root and leaf conditions of tobacco seedlings after 15 days of treatment (bars=10 cm); (B) Length of the longest root; (C) Total root length; (D) Root surface area; (E) Root volume; (F) Number of root tips. Different lowercase letters indicate significant differences among different treatments (P<0.05).

Figure 2 Potassium concentration in tobacco plants and xylem sap under different potassium concentration treatments (A) Potassium ion concentrations of the aboveground and underground parts; (B) Xylem sap collection volume; (C) Potassium accumulation in the aboveground and underground parts; (D) Potassium ion concentration in the xylem sap. Different lowercase letters indicate significant differences among different treatments (P<0.05).

Figure 3 Differences in the levels of endogenous hormones in tobacco roots under different potassium concentrations (A) Root endogenous abscisic acid (ABA) concentration; (B) Root endogenous ethylene (ETH) concentration; (C) Root endogenous methyl jasmonate (MeJA) concentration. Different lowercase letters indicate significant differences among different treatments (P<0.05).

Figure 4 Imaging and schematic diagram of the three types of suberin development stages Bars=130 μm

Figure 5 Developmental status of three suberized regions in the endodermis of tobacco roots under different potassium concentration treatments (A) Absolute lengths; (B) Relative lengths. Different lowercase letters indicate significant differences among different treatments (P<0.05).

Figure 6 Fluorescence images of transverse sections of endodermis development in tobacco roots at three potassium concentrations (A) Schematic diagram of the suberization development in the endodermis of tobacco roots at three potassium concentrations; (B) FY 088 fluorescence imaging of different root segment cross-sections of tobacco at three potassium concentrations (bars=130 μm); (C) Absolute length and relative length of suberization development in the endodermis of tobacco roots at three potassium concentrations

Figure 7 Differential expression of genes response to 0.1 mmol∙L-1 K+ treatment FC: Fold change

Figure 8 KEGG and GO enrichment analyses of differentially expressed genes (DEGs) under 0.1 mmol∙L-1 K+ treatment MF: Molecular function; CC: Cellular component; BP: Biological process

Figure 9 Expression levels of endodermal suberization-related genes, MYB transcription factors, and potassium transporter-related genes among the differentially expressed genes under 0.1 mmol∙L-1 K+ treatment

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