Junliang Xin

Variation in Cadmium Accumulation among 30 Cultivars and Cadmium Subcellular Distribution in 2 Selected Cultivars of Water Spinach (Ipomoea aquatica Forsk.)

To reduce the influx of cadmium (Cd), a toxic heavy metal, into the human food chain through vegetable intake, a pot experiment for the selection of a pollution-safe cultivar (PSC) of water spinach (Ipomoea aquatica Forsk.) was carried out. The experiment with 30 tested cultivars revealed that the maximum differences in Cd concentration between the cultivars containing the highest and the lowest Cd were 3.0-3.9-fold under low-Cd treatment (soil Cd = 0.593 mg kg(-1)), 2.7-3.5-fold under middle-Cd treatment (soil Cd = 1.091 mg kg(-1)), and 2.6-2.7-fold under high-Cd treatment (soil Cd = 1.824 mg kg(-1)), large enough to define the Cd-PSCs. Concentrations of Cd in edible parts of six cultivars, cv. Daxingbaigu, Huifengqing, Qiangkunbaigu, Qiangkunqinggu, Shenniuliuye, and Xingtianqinggu, were lower than 0.2 mg kg(-1), the maximum level (ML) of Cd allowed by the Codex Alimentarius Commission (CAC) standard, even under middle-Cd treatment. Accordingly, these cultivars were treated as typical Cd-PSCs. Four cultivars, cv. Jieyangbaigeng, Xianggangdaye, Sannongbaigeng, and Taiwan 308, contained Cd in edible parts exceeding the ML even under low-Cd treatment, and they were defined as typical non-Cd-PSCs. The correlations of the Cd concentrations among the tested cultivars between the three treatments were significant at the p < 0.05 level. A conspicuous difference in Cd subcellular distribution in hydroponic plant tissues between cv. Qiangkunqinggu (a typical Cd-PSC) and cv. Taiwan 308 (a typical non-Cd-PSC) were observed. Cd absorbed by cv. Qiangkunqinggu seemed to be well-compartmentalized in root and in cell wall fragment, which may be one of the mechanisms leading to its low Cd accumulating property. The results indicated that water spinach, a leafy vegetable, could be easily polluted by soils contaminated with Cd, as 80% of the tested cultivars had exceeded the ML of Cd according to the CAC standard even under the middle-Cd treatment. Much of the evidence obtained from the present study proved that the high Cd-accumulating ability of water spinach is a stable biological property at cultivar level and, thus, is genotype dependent. Therefore, application of the PSC strategy to produce water spinach that is safer to consume is feasible and necessary.

Responses of different water spinach cultivars and their hybrid to Cd, Pb and Cd–Pb exposures

A pot experiment was conducted to investigate the stability of Cd and/or Pb accumulation in shoot of Cd and Pb pollution-safe cultivars (PSCs), the hereditary pattern of shoot Cd accumulation, and the transfer potentials of Cd and Pb in water spinach (Ipomoea aquatica Forsk.). A typical Cd-PSC, a typical non-Cd-PSC (Cd accumulative cultivar), a hybrid from the former two cultivars, and two typical Cd+Pb-PSCs were grown in seven soils with different concentrations of Cd and Pb. The results showed that concentrations of Cd and Pb in shoot of the PSCs were always lower than the non-PSC and the highest Cd and Pb transfer factors were also always observed in the non-PSC, indicating the stability of the PSCs in Cd and Pb accumulation. Shoot Cd concentration seemed to be controlled by high Cd dominant gene(s) and thus crossbreeding might not minimize Cd accumulation in water spinach. Interaction between Cd and Pb in soils affected the accumulations of the metals in shoot of water spinach. Under middle Cd and Pb treatments, the presence of higher Pb promoted the accumulation of Cd. However, under high Pb treatment, accumulations of Cd and Pb were both restricted.

Comparison of cadmium subcellular distribution in different organs of two water spinach (Ipomoea aquatica Forsk.) cultivars

AimsMechanisms of low cadmium (Cd) accumulations in cultivars of water spinach are poorly investigated. We aimed to improve understanding of the subcellular biochemical properties of the mechanisms involved.MethodsA pot experiment was conducted to investigate the subcellular distributions of Cd in lateral and main roots, stems, and young and old leaves of a high-Cd (T308) and a low-Cd cultivar (QLQ).ResultsThe ratio of main root:lateral roots Cd concentration in QLQ was lower (0.34–0.35) than that in T308 (0.39–0.55). The ratio of stem:main root Cd concentration in QLQ was much lower (0.60–0.73) than that in T308 (1.19–1.58). QLQ has higher capacity to sequester Cd in cell wall fractions of main and lateral roots than T308.ConclusionsThe difference in shoot Cd concentration between QLQ and T308 is attributable to the difference in Cd translocation from lateral to main roots and from roots to the stem. Fixation of large amounts of Cd in old leaves is beneficial to protect young leaves from Cd toxicity. Cadmium immobilization by the cell wall is important in Cd detoxification, especially in main and lateral roots of QLQ and the shoot of T308.

Role of roots in cadmium accumulation of two water spinach cultivars: reciprocal grafting and histochemical experiments

Background and AimsCultivars of water spinach (Ipomoea aquatica Forsk.) differ widely in their shoot cadmium (Cd) concentration. Previously, we suggested that low-Cd cultivars are better able to retain Cd in their roots and thus prevent root-to-shoot Cd translocation. In this study, we explored the roles of roots and shoots in Cd accumulation in a high-Cd (T308) and low-Cd cultivar (QLQ).MethodsWe used reciprocal grafting to determine the importance of roots and shoots in Cd accumulation, and a dithizone histochemical method to investigate Cd distribution in the roots.ResultsThe T308 scion with QLQ rootstock accumulated less Cd than the shoot of non-grafted T308. The QLQ scion with T308 rootstock showed a significantly higher Cd concentration than that in the shoot of non-grafted QLQ. Cadmium induced thicker phellem formation in the main roots of QLQ than in those of T308 and only QLQ showed thickening of the outer cortex cell walls in lateral roots.ConclusionsShoot Cd accumulation was primarily determined by root-to-shoot Cd translocation, not root Cd uptake. The thicker phellem and outer cortex cell walls in QLQ than in T308 may be one reason why QLQ roots were able to retain more Cd, and thus reducing Cd translocation to shoots.

Suppression subtractive hybridization (SSH)-based method for estimating Cd-induced differences in gene expression at cultivar level and identification of genes induced by Cd in two water spinach cultivars.

The abilities to accumulate cadmium (Cd) are different among cultivars (cv.) in many species. The characteristic of Cd concentration among cultivars is heritable and is probably controlled by genes, but rather limited information about the relevant genes in vegetable crops has been published. In the present study, a suppression subtractive hybridization (SSH) approach was used to identify genes induced by Cd in two water spinach (an important vegetable in southern China) cultivars that differ in Cd accumulation in their edible parts. The two cultivars were cv. Qiangkunqinggu (QK), a low Cd accumulative cultivar and cv. Taiwan 308 (TW), a high Cd accumulative cultivar. In the construction of QK and TW libraries, the plants without Cd treatment were taken as drivers and the plants exposed to 6 mg L(-1) Cd for 24 h as testers. Four hundred clones were sequenced, and 164 nonrepeated sequences (112 from the QK library and 52 from the TW library) were assigned to being functional genes or proteins. A tremendous difference in Cd-induced gene expressions between the two libraries was observed. In the QK library, genes implicated in disease/defense comprised one of the largest sets (20.6%), whereas the proportion was only 8.8% in the TW library. An MT3 gene (Q5), a wound inductive gene (Q22), an antioxidation relevant gene (Q34), a lectin gene (Q45), an f-box family protein gene (Q319), a 20S proteasome subunit gene (T17), a multidrug resistance associated protein gene (T156), and a cationic amino acid transporter gene (T218) were selected to compare semiquantitatively their expression between cv. QK and cv. TW using the RT-PCR method, and obvious differences were detected. The relationships between the identified differences in the expressions of the genes and the Cd accumulation of the two cultivars were discussed, and it was concluded that the SSH approach is useful for finding the difference in expression of Cd-induced gene even at the cultivar level and is applicable in the investigation of the mechanisms of low Cd accumulation.

Genotype variations in accumulation of cadmium and lead in celery (Apium graveolens L.) and screening for low Cd and Pb accumulative cultivars

To help reduce risks of heavy metal pollution, two pot experiments were conducted to investigate the variations, transfer potential, and stability of Cadmium (Cd) and Lead (Pb) accumulations in celery (Apium graveolens L.) and to screen for low Cd and Pb accumulative cultivars. The maximum differences in shoot Cd concentration were 4.7-fold under low-Cd exposure and 3.3-fold under high-Cd exposure. These genotype variations in Cd accumulation are sufficiently large to help reduce Cd contamination risk in soil by using the Low-Cd-Accumulative genotypes. Cd accumulation of the Low-Cd-Accumulative genotypes is significantly positive correlated with Pb accumulation. Evidence obtained proves that Cd and Pb accumulations in celery are stable and genotype-dependent at the cultivar level. The presence of high-Pb contamination in soil promoted Cd accumulation in shoots of celery. Celery is considered a species with high risks in Cd pollution and low risks in Pb pollution. Among the tested cultivars, cv. Shuanggangkangbing (SGKB) had the lowest shoot Cd and Pb accumulating abilities, and thus is the most important material for breeding of pollution-safe cultivars (PSCs) to minimize Cd and Pb accumulations in celery.

Effects of Interaction between Cadmium (Cd) and Selenium (Se) on Grain Yield and Cd and Se Accumulation in a Hybrid Rice (Oryza sativa) System

A pot experiment was conducted to investigate the interactive effects of cadmium (Cd) and selenium (Se) on their accumulation in three rice cultivars, which remains unclear. The results showed that Se reduced Cd-induced growth inhibition, and increased and decreased Se and Cd concentrations in brown rice, respectively. Cadmium concentrations in all tissues of the hybrid were similar to those in its male parent yet significantly lower than those in its female parent. Selenium reduced Cd accumulation in rice when Cd concentration exceeded 2.0 mg kg-1; however Se accumulation depended on the levels of Cd exposure. Finally, Cd had minimal effect on Se translocation within the three cultivars. We concluded that Cd concentration in brown rice is a heritable trait, making crossbreeding a feasible method for cultivating high-yield, low-Cd rice cultivars. Selenium effectively decreased the toxicity and accumulation of Cd, and Cd affected Se uptake but not translocation.