Effect of cadmium on the chemical composition of xylem exudate from oilseed rape plants (Brassica napus L.)

Figures & data

Table 1 Effects of the chemical composition of the xylem exudate from oilseed rape plants on Cd treatment

Substance	Concentration
	Treatment
	Control	Cd treated (48 h)
		10 µmol L^−1	30 µmol L^−1
Sugars
Glucose	0.304 ± 0.048 mmol L^−1	0.071 ± 0.052 mmol L^−1	0.098 ± 0.041 mmol L^−1
Fructose	0.087 ± 0.027 mmol L^−1	0.085 ± 0.034 mmol L^−1	0.026 ± 0.031 mmol L^−1
Sucrose	trace	trace	trace
Organic acids
Malic acid	0.74 ± 0.30 mmol L^−1	0.85 ± 0.41 mmol L^−1	0.76 ± 0.36 mmol L^−1
Citric acid	0.50 ± 0.22 mmol L^−1	0.64 ± 0.11 mmol L^−1	0.54 ± 0.15 mmol L^−1
Anions
Nitrate	15.58 ± 1.29 mmol L^−1	21.39 ± 2.05 mmol L^−1	18.89 ± 1.19 mmol L^−1
Sulfate	6.78 ± 0.31 mmol L^−1	7.24 ± 1.14 mmol L^−1	7.86 ± 0.27 mmol L^−1
Phosphate	4.02 ± 0.64 mmol L^−1	4.55 ± 0.62 mmol L^−1	1.84 ± 0.42 mmol L^−1
Inorganic cations
Calcium	7.56 ± 0.20 mmol L^−1	6.78 ± 0.49 mmol L^−1	6.99 ± 0.62 mmol L^−1
Potassium	6.37 ± 0.36 mmol L^−1	6.15 ± 0.44 mmol L^−1	9.96 ± 1.68 mmol L^−1
Magnesium	3.49 ± 0.11 mmol L^−1	3.80 ± 0.28 mmol L^−1	3.64 ± 0.23 mmol L^−1
Sodium	0.78 ± 0.06 mmol L^−1	1.02 ± 0.16 mmol L^−1	0.60 ± 0.05 mmol L^−1
Manganese	23.3 ± 3.2 µmol L^−1	26.5 ± 1.7 µmol L^−1	25.9 ± 1.8 µmol L^−1
Iron	10.4 ± 3.5 µmol L^−1	11.2 ± 2.5 µmol L^−1	14.9 ± 3.9 µmol L^−1
Zinc	2.45 ± 0.46 µmol L^−1	1.22 ± 0.40 µmol L^−1	2.85 ± 1.56 µmol L^−1
Copper	0.55 ± 0.11 µmol L^−1	2.62 ± 0.95 µmol L^−1	4.04 ± 0.33 µmol L^−1
Xylem exudates were collected from 6-week-old plants. All values are mean ± standard deviation (n = 3).

Figure 1  Effect of Cd treatment on the protein concentration of the xylem exudates collected from oilseed rape plants. Plants were treated with 10 µmol L−1 and 30 µmol L−1 Cd-containing hydroponic solution for 48 h and the xylem exudates were collected after this time. Data are the mean ± standard deviation of three independent samples.

Table 2 Amino acid concentrations in the xylem exudate from oilseed rape plants treated with 0 (control), 10 or 30 µmol L−1 Cd for 48 h

	Amino acids concentration (mmol L^−1)
	Treatment
	Control	Cd treated (48 h)
		10 µmol L^−1	30 µmol L^−1
Ala	0.065 ± 0.016	0.221 ± 0.088	0.050 ± 0.027
Arg	0.082 ± 0.029	0.098 ± 0.033	0.079 ± 0.029
Asp	2.038 ± 0.651	0.280 ± 0.258	0.628 ± 0.692
AspNH2	0.178 ± 0.065	0.150 ± 0.022	0.154 ± 0.043
Cys	N.D.	0.027 ± 0.047	0.062 ± 0.054
Glu	0.092 ± 0.039	0.210 ± 0.125	0.110 ± 0.027
GluNH2	4.924 ± 1.021	4.202 ± 0.215	3.262 ± 0.676
Gly	0.037 ± 0.007	0.055 ± 0.039	0.018 ± 0.004
His	0.076 ± 0.013	0.066 ± 0.009	0.069 ± 0.019
Ile	0.113 ± 0.031	0.151 ± 0.014	0.141 ± 0.021
Leu	0.064 ± 0.029	0.065 ± 0.003	0.086 ± 0.015
Lys	0.170 ± 0.071	0.134 ± 0.015	0.168 ± 0.039
Met	0.029 ± 0.021	0.044 ± 0.008	0.045 ± 0.005
Phe	0.011 ± 0.013	0.038 ± 0.006	0.036 ± 0.005
Pro	N.D.	0.018 ± 0.015	0.019 ± 0.032
Ser	0.107 ± 0.004	0.189 ± 0.049	0.068 ± 0.035
Thr	0.181 ± 0.073	0.201 ± 0.028	0.170 ± 0.026
Trp	N.D.	N.D.	N.D.
Tyr	0.032 ± 0.013	0.062 ± 0.005	0.054 ± 0.005
Val	0.135 ± 0.052	0.141 ± 0.003	0.152 ± 0.023
Total	8.334 ± 0.020	6.353 ± 0.542	5.369 ± 0.833
All values are mean ± standard deviation (n = 3). N.D., under detection limit.

Figure 2  Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of proteins in the xylem exudates and proteins extracted from the roots, stems and leaves of oilseed rape plants. Three micrograms of protein was subjected to SDS-PAGE analysis and detected using silver staining in each lane.

Figure 3  Cadmium concentration in the xylem exudate collected from oilseed rape plants. Plants were treated with 10 µmol L−1 (○) and 30 µmol L−1 (•) Cd for 24, 48 and 72 h. Data are the mean ± standard deviation of three independent samples.

Table 3 Content of amino acids as a percentage of the total amino acids in the xylem exudate of oilseed rape plants

	Percentage of amino acids (%)
	Treatment
	Control	Cd treated (48 h)
		10 µmol L^−1	30 µmol L^−1
Ala	0.78 ± 0.19	3.51 ± 1.53	0.93 ± 0.45
Arg	0.98 ± 0.34	1.55 ± 0.54	1.46 ± 0.38
Asp	24.46 ± 7.80	4.22 ± 3.56	11.14 ± 11.52
AspNH2	2.14 ± 0.78	2.37 ± 0.35	2.90 ± 0.77
Cys	0.00 ± 0.00	0.46 ± 0.79	1.23 ± 1.11
Glu	1.10 ± 0.47	3.21 ± 1.65	2.07 ± 0.46
GluNH2	59.09 ± 12.27	66.31 ± 3.82	61.14 ± 10.79
Gly	0.44 ± 0.08	0.89 ± 0.69	0.35 ± 0.10
His	0.91 ± 0.16	1.05 ± 0.16	1.30 ± 0.37
Ile	1.35 ± 0.37	2.38 ± 0.19	2.65 ± 0.34
Leu	0.77 ± 0.35	1.03 ± 0.06	1.61 ± 0.27
Lys	2.04 ± 0.85	2.13 ± 0.38	3.10 ± 0.28
Met	0.35 ± 0.26	0.70 ± 0.13	0.84 ± 0.06
Phe	0.13 ± 0.16	0.59 ± 0.04	0.69 ± 0.18
Pro	0.00 ± 0.00	0.27 ± 0.24	0.32 ± 0.55
Ser	1.28 ± 0.05	2.95 ± 0.55	1.26 ± 0.58
Thr	2.17 ± 0.87	3.16 ± 0.28	3.16 ± 0.06
Trp	0.00 ± 0.00	0.00 ± 0.00	0.00 ± 0.00
Tyr	0.39 ± 0.15	0.98 ± 0.10	1.01 ± 0.07
Val	1.62 ± 0.63	2.23 ± 0.15	2.85 ± 0.36
Total	100.00 ± 0.00	100.00 ± 0.00	100.00 ± 0.00
All values are mean ± standard deviation (n = 3).

Figure 4  Analysis of xylem exudate proteins using sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Xylem exudate samples were collected from control plants and 6-week-old plants were transferred to a hydroponic solution containing 10 µmol L−1 and 30 µmol L−1 Cd (CdCl2) and treated for 48 h. Three micrograms of protein was subjected to SDS-PAGE analysis and detected using silver staining in each lane.