Chin J Plan Ecolo ›› 2017, Vol. 41 ›› Issue (6): 683-692.doi: 10.17521/cjpe.2016.0136

• Research Articles • Previous Articles     Next Articles

Metabolic responses of wheat roots to alkaline stress

Rui GUO1,2,*(), Ji ZHOU3, Fan YANG4, Feng LI1   

  1. 1Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China

    2Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Beijing 100081, China

    3Land Consolidation and Rehabilitation Centre, the Ministry of Land and Resources, Beijing 100034, China
    and
    4Jilin Academy of Forestry Science, Changchun 130033, China
  • Received:2017-04-05 Accepted:2016-04-14 Online:2017-07-19 Published:2017-06-10
  • Contact: Rui GUO E-mail:guorui01@caas.cn
  • About author:

    KANG Jing-yao(1991-), E-mail: kangjingyao_nj@163.com

Abstract:

Aims The aim of this study was to investigate the effects of alkaline stress on primary, secondary metabolites and metabolic pathways in the roots of wheat (Triticum aestivum). The results were used to evaluate the physiological adaptive mechanisms by which wheat tolerated alkali stress.Methods A pot experiment was carried out in the greenhouse. For each plastic pot, five wheat seeds were planted. After germination, seedlings were allowed to grow under controlled water and nutrient conditions for two months, then seedlings were exposed to alkaline stress (NaHCO3-Na2CO3) for 12 days. The relative growth rate (RGR), absolute water content (AWC), metal elements, free cations and metabolites were measured.Important findings The alkaline stress caused the reduction of RGR and AWC. Alkaline stress caused a rapid increase of Na content with the concurrent decrease in K and Cl content, resulting in inhibited metal element accumulation and an ionic imbalance. In the present study, alkaline stress strongly enhanced Ca accumulation in wheat roots, suggesting that an increased Ca concentration can immediately trigger the salt overly sensitive (SOS)-Na exclusion system and reduce Na-associated injuries. Also, 70 metabolites, including organic acids, amino acids, sugars/polyols and others, behaved differently in the alkaline stress treatments according to a GC-MS analysis. The metabolic profiles of wheat were closely associated with alkaline-stress conditions. Alkaline stress caused the accumulation of organic acids, accompanied by the depletion of sugars/polyols and amino acids. Organic acids could play a central role in the regulation of intracellular pH by accumulating vacuoles to neutralize excess cations. Glycolysis and amino acid synthesis in roots were inhibited under salt stress while prolonged alkaline stress led to a progressive tricarboxylic acid (TCA) cycle. The severe negative effects of alkaline stress on sugar synthesis and storage may reflect the toxic levels of Na+ accumulating in plant cells in a high-pH environment, implying that the reactive oxygen species detoxification capacity was diminished by the high pH. A lack of NO3- in wheat roots can decrease synthase enzyme activities, limiting the synthesis of amino acids. Under salt stress, the TCA cycle and organic acid accumulation increased, but glycolysis and amino acid synthesis were inhibited in roots. Thus, energy levels and high concentrations of organic acids may be the key adaptive mechanisms by which wheat seedlings maintain their intracellular ion balance under alkaline stress.

Key words: wheat (Triticum aestivum), alkaline stress, roots, growth characters, metabolic profiles

Table 1

The electrical conductivity (EC), pH value and osmotic potential of salinity stress treatment solutions"

处理
Treatment
碱浓度
Alkaline
concentration
(mmol·L-1)
电导率
EC (dS·m-1)
渗透势
Osmotic potential
(MPa)
pH值
pH value
对照 Control 0 2.16 -0.05 6.95
碱胁迫
Alkaline stress
50 4.98 -0.28 9.69
100 9.21 -0.51 9.92

Fig. 1

Effects of alkaline concentration on root relative growth rate (RGR) and absolute water content (AWC) (mean ± SE, n = 5). Different lowercase letters indicate significant differences among the various treatments (p < 0.05)."

Table 2

Effects of alkaline stress on the contents of metal elements in the roots of wheat seedlings (mean ± SE, n = 5)"

处理
Treatment
碱胁迫浓度
Alkaline concentration
(mmol)
矿质元素 Metal elements (mmol·g-1 dry mass)
Na K Ca Mg Cu Fe Zn Mn
对照 Control 0 4.25 ± 1.01b 69.90 ± 3.03a 17.11 ± 1.01b 7.80 ± 0.29a 1.25 ± 0.04a 1.56 ± 0.08a 0.07 ± 0.01a 0.06 ± 0.00a
碱胁迫
Alkaline stress
50 15.89 ± 2.06 ab 45.20 ± 1.54b 20.53 ± 1.00b 6.01 ± 0.16b 1.02 ± 0.02a 1.26 ± 0.03a 0.05 ± 0.00b 0.05 ± 0.00a
100 19.09 ± 2.11a 16.83 ± 1.02c 32.85 ± 1.30a 4.96 ± 0.47c 0.55 ± 0.03b 0.84 ± 0.05b 0.03 ± 0.00c 0.06 ± 0.00a

Table 3

Effects of alkaline stress on the contents of Cl-, NO3-, H2PO4-, SO42- in the roots of wheat seedlings (mean ± SE, n = 5)."

处理
Treatment
碱胁迫浓度
Alkaline concentration (mmol)
阴离子 Anions (mmol·g-1 dry mass)
Cl- NO3- H2PO4- SO42-
对照 Control 0 0.12 ± 0.01a 0.41 ± 0.02a 0.05 ± 0.00a 0.03 ± 0.00a
碱胁迫 Alkaline stress 50 0.09 ± 0.00b 0.34 ± 0.01b 0.03 ± 0.01b 0.02 ± 0.00a
100 0.04 ± 0.01c 0.07 ± 0.00c 0.02 ± 0.00b 0.03 ± 0.00a

Fig. 2

SIMCA analyzed score plots showing the metabolomic trajectory of roots of wheat seedlings under different salinity concentration treatments. Principal component analysis (PCA) score plots (A). Orthogonal partial least squares discriminant analysis (OPLS-DA) scores: CK vs. AS-50 mmol·L-1 (B) and CK vs. AS-100 mmol·L-1 (C)."

Table 4

Relative concentration and changes of major metabolites in roots of wheat seedlings after alkaline stress treatment"

代谢路径和代谢物名称
Metabolic pathways and metabolites
相对含量 Relative concentration 倍性变量Fold changes
CK AS-50 mmol AS-100 mmol log2(50/CK) log2(100/CK)
三羧酸循环
Tricarboxylic acid cycle
柠檬酸 Citric acid 75.73 150.14 231.23 0.99* 1.61**
乌头酸 Aconitic acid 1.34 1.70 5.13 0.34 1.93**
α-酮戊二酸 α-ketoglutaric acid 0.18 0.33 0.85 0.89 2.23**
琥珀酸 Succinic acid 19.05 61.45 120.69 1.69** 2.66**
延胡索酸 Fumaric acid 1.34 1.56 9.63 0.23 2.85**
苹果酸 Malic acid 10.47 23.10 30.35 1.14* 1.54**
糖酵解过程
Glycolysis
葡萄糖 Glucose 26.37 13.67 7.91 -0.95* -1.74**
葡萄糖-6-磷酸 Fructose-6-phosphate 0.57 0.25 0.08 -1.16* -2.75**
果糖-6-磷酸 Glucose-6-phosphate 0.22 0.13 0.04 -0.80 -2.58**
3-磷酸甘油酸 3-phosphoglyceric acid 0.50 0.34 0.11 -0.57 -2.19**
丙酮酸 Pyruvate 0.54 0.50 0.31 -0.10 -0.81
磷酸烯醇式丙酮酸 Enolphosphopyruvate 0.73 0.61 0.22 -0.26 -1.74**
莽草酸途径
Shikimic path way
莽草酸 Shikimic acid 1.84 1.22 3.84 -0.60 1.06*
奎尼酸 Quinic acid 4.17 6.17 23.11 0.58 2.47**
苯丙氨酸 Phenylalanine 0.65 0.17 0.11 -1.91* -2.60**
色氨酸 Tryptophan 0.05 0.03 0.02 -0.71 -1.45*
酪氨酸 Tyrosine 1.59 0.03 0.02 -4.18** -6.57**
肉桂酸 Cinnamic acid 0.25 0.15 0.12 -0.77 -1.12*
细胞膜脂代谢
Metabolism of
plasma membrane
肌醇 Myo-inositol 19.17 9.63 3.07 -0.99* -2.64**
甘氨酸 Glycine 0.74 0.34 0.12 -1.56** -2.69**
丝氨酸 Serine 17.83 9.56 1.64 -0.90* -3.44**
乙醇胺 Ethanolamine 20.23 11.31 3.26 -0.84* -2.63**
氨基酸
Amino acid
γ-氨基丁酸 γ-aminobutyric acid 137.19 41.77 23.92 -1.72** -2.52**
丙氨酸 Alanine 106.58 56.88 10.64 -0.91* -3.32**
谷氨酸 Glutamate 24.93 13.73 8.40 -0.86* -1.57**
天冬酰胺 Asparagine 12.65 4.38 0.91 -1.53** -3.79**
天冬氨酸 Aspartic acid 7.60 4.06 3.34 -0.90* -1.19*
脯氨酸 Proline 10.04 15.47 11.57 0.62 0.20
赖氨酸 Lysine 17.32 0.33 0.11 -5.72** -7.26**
糖类及多元醇
Sugars and polyols
果糖 Fructose 814.31 574.62 173.68 -0.78* -2.23**
蔗糖 Sucrose 136.11 92.04 65.17 -0.56 -1.06*
塔罗糖 Talose 114.17 75.07 23.13 -0.60 -2.30**
蔗果三糖 Kestose 57.63 42.47 19.69 -0.44 -1.55**
核糖 Ribose 8.24 4.25 1.38 -0.96* -2.58**

Fig. 3

Proposed metabolic network changes for wheat roots upon alkaline stress obtained from OPLS-DA analysis. The metabolite with white boxes denotes no significant change while red boxes denotes significant increases and green ones denotes significant decreases (p < 0.05)."

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