Chemical Composition of Root and Stem Saps in Relation to Cadmium Resistance and Accumulation in Brassica parachinensis

doi:10.1016/S1002-0160(07)60042-3

Pedosphere

Volume 17, Issue 3, June 2007, Pages 352-359

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Abstract

Sap mixtures of the xylem, phloem, and vacuoles from low and high Cd accumulator varieties of Brassica parachinensis L. H. Bailey were analyzed under Cd stress to understand the biochemical mechanisms of Cd accumulation in plants. Low Cd accumulator (‘Teqing-60’) and high Cd accumulator (‘Chixin-2’) plants were grown in Cd-treated soil in pots in a greenhouse. Percentage of cell wall-bound Cd was estimated. pH level and the concentrations of amino acids, organic acids, anions, and cations in both stem and root saps were determined for the calculation of Cd speciations using the computer program GEOCHEM. The results showed that ‘Teqing-60’ had a significantly higher (P ≤ 0.05) percentage of Cd bound to cell walls in roots and a significantly higher (P ≤ 0.05) pH in the root sap. ‘Teqing-60’ also contained a higher concentration of total amino acids in both roots and stems compared with the high Cd accumulator variety ‘Chixin-2’. However, between the two accumulators, for stems and for roots, there were no significant differences in non-amino organic acids. GEOCHEM calculations showed that Cd in the root sap of ‘Teqing-60’ mainly combined with amino acids, especially alanine. Compared with ‘Chixin-2’, in the root sap of ‘Teqing-60’, much lower levels of Cd as free ions or bound to simple ligands were found, indicating that less ‘Teqing-60’ is transferred to stems and leaves. Cadmium activity in the shoot sap of ‘Teqing-60’ was much lower than that in ‘Chixin-2’; therefore, ‘Teqing-60’ exhibited higher Cd resistance. However, direct determination of the Cd complexes from xylem and phloem sap is needed to verify these results.

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Cited by (5)

Root cell walls and phytochelatins in low-cadmium cultivar of Brassica parachinensis
2020, Pedosphere
‘Lvbao-701’ is a cultivar of Chinese flowering cabbage (Brassica parachinensis) that exhibits low cadmium (Cd) accumulation and high Cd tolerance. In this study, this cultivar was compared with a high-Cd accumulating cultivar, ‘Chixin-4’, to characterize the mechanisms influencing Cd accumulation in B. parachinensis. Root cell walls were isolated by dissolving the cytoplasm with an organic solvent, and root Cd and phytochelatin (PC) contents were analyzed. In addition, a PC synthase gene fragment was cloned and expressed under Cd stress conditions. The proportions of Cd bound to root cell walls were higher in the ‘Lvbao-701’ plants (68.32%–76.80%) than in the ‘Chixin-4’ plants (35.36%–54.18%) after exposure to Cd stress. The proportions of Cd bound to root cell walls measured using cell walls isolated with a non-destructive method were higher than those obtained using a conventional method that required grinding and centrifugation. Exposure to Cd stress induced the PC production and resulted in higher PC contents in the ‘Lvbao-701’ plants than in the ‘Chixin-4’ plants. Cloning and expression analysis of a B. parachinensis PC synthase cDNA fragment indicated that PC synthase gene expression was induced by Cd and occurred mainly in the roots of both ‘Lvbao-701’ and ‘Chixin-4’ plants. However, the PC synthase gene expression level was higher in the ‘Lvbao-701’ roots than in the ‘Chixin-4’ roots. Therefore, a higher abundance of Cd in the root cell walls of ‘Lvbao-701’ and up-regulated PC production in the roots are probably the main reasons why ‘Lvbao-701’ exhibits lower Cd translocation to the shoots and higher tolerance to Cd than ‘Chixin-4’.
Cadmium remobilization from shoot to grain is related to pH of vascular bundle in rice
2018, Ecotoxicology and Environmental Safety
Citation Excerpt :
Under water stress condition, pH of xylem sap affected on transpirations by regulating stomatal movement (Gollan et al., 1992; Mak et al., 2014; Sharp and Davies, 2009; Wilkinson and Davies, 1997). pH also affects the concentration of organic acids (Gallego et al., 2012; Wu et al., 2007), which would be influence on chemical forms of Cd in the xylem sap. It was verified that pH shifts could cause in protein conformational changes, thus having pronounced effects on membrane transporters (Felle et al., 2001; Watanabe and Osaki, 2001).
The remobilization of cadmium (Cd) from shoots to grain is the key process to determine the Cd accumulation in grain. The apoplastic pH of plants is an important factor and signal in influencing on plant responding to environmental variation and inorganic elements uptake. It is proposed that pH of rice plants responds and influences on Cd remobilization from shoots to grain when rice is exposed to Cd stress. The results of hydroponic experiment showed that: pH of the rice leaf vascular bundles among 3 cultivars was almost increased, pH value of 1 cultivar was slightly increasing when rice plants were treated with Cd. The decrease degree of H⁺ concentration in leaf vascular bundles was different among cultivars. The cultivar with higher decreasing in H⁺ concentration, showed higher Cd transfer efficiency from shoots to grain. The H⁺ concentration of leaf vascular bundles under normal condition was negatively correlated to cadmium accumulation in leaf. Moreover, pH change was related to Cd accumulation in shots and remobilization from shoots to grain. Uncovering the role of pH response is a key component for the understanding Cd uptake and remobilization mechanism for rice production.
Advances in remediation of acid agricultural soils contaminated by heavy metals in South China
2018, Twenty Years of Research and Development on Soil Pollution and Remediation in China
Tobacco cadmium health risk assessment and reduction techniques: A review
2015, Chinese Journal of Applied Ecology
Contribution of cell walls, nonprotein thiols, and organic acids to cadmium resistance in two cabbage varieties
2013, Archives of Environmental Contamination and Toxicology

¹: Project supported by the National Natural Science Foundation of China (No. 40571141) and the Natural Science Foundation of Guangdong Province (No. 021007) and the Key Teachers Foundation of the Ministry of Education of China (No. 2000-143-39).

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Pedosphere

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References (19)

Cadmium distribution and chemical fate in soybean plant

Plant Physiol

Differential Cadmium accumulation and phytotoxicity in sixteen tobacco cultivars

Journal of the Air and Waste Management Association

Uptake and distribution of cadmium in maize inbred lines: Effect of pH and level of Cd supply

Plant and Soil

Cd availability to three plant species varying in Cd accumulation pattern

J. Environ. Qual

Uptake, distribution and binding of cadmium and nickel in different species

J. Plant Nutri

Characterization of cadmium binding, uptake, and translocation in intact seedlings of bread and durum wheat cultivars

Plant Physiol

Uptake, distribution and accumulation of copper in two ecotypes of Elsholtzia

Pedosphere

Metal speciation in xylem and phloem exudates

Plant and Soil

Cited by (5)

Root cell walls and phytochelatins in low-cadmium cultivar of Brassica parachinensis

Cadmium remobilization from shoot to grain is related to pH of vascular bundle in rice

Advances in remediation of acid agricultural soils contaminated by heavy metals in South China

Tobacco cadmium health risk assessment and reduction techniques: A review

Contribution of cell walls, nonprotein thiols, and organic acids to cadmium resistance in two cabbage varieties

Chemical Composition of Root and Stem Saps in Relation to Cadmium Resistance and Accumulation in Brassica parachinensis1

Abstract

Cadmium distribution and chemical fate in soybean plant

Plant Physiol

Differential Cadmium accumulation and phytotoxicity in sixteen tobacco cultivars

Journal of the Air and Waste Management Association

Uptake and distribution of cadmium in maize inbred lines: Effect of pH and level of Cd supply

Plant and Soil

Cd availability to three plant species varying in Cd accumulation pattern

J. Environ. Qual

Uptake, distribution and binding of cadmium and nickel in different species

J. Plant Nutri

Characterization of cadmium binding, uptake, and translocation in intact seedlings of bread and durum wheat cultivars

Plant Physiol

Uptake, distribution and accumulation of copper in two ecotypes of Elsholtzia

Pedosphere

Metal speciation in xylem and phloem exudates

Plant and Soil

Chemical Composition of Root and Stem Saps in Relation to Cadmium Resistance and Accumulation in Brassica parachinensis¹