Zinc (Zn) is an essential component of thousands of proteins in plants, although it is toxic in excess. In this review, the dominant fluxes of Zn in the soil-root-shoot continuum are described, including Zn inputs to soils, the plant availability of soluble Zn(2+) at the root surface, and plant uptake and accumulation of Zn. Knowledge of these fluxes can inform agronomic and genetic strategies to address the widespread problem of Zn-limited crop growth. Substantial within-species genetic variation in Zn composition is being used to alleviate human dietary Zn deficiencies through biofortification. Intriguingly, a meta-analysis of data from an extensive literature survey indicates that a small proportion of the genetic variation in shoot Zn concentration can be attributed to evolutionary processes whose effects manifest above the family level. Remarkable insights into the evolutionary potential of plants to respond to elevated soil Zn have recently been made through detailed anatomical, physiological, chemical, genetic and molecular characterizations of the brassicaceous Zn hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri.

Zinc in plants

Heavy metal hyperaccumulating plants: how and why do they do it? And what makes them so interesting?

http://www.irrec.ifas.ufl.edu/IRSWS/History%20Publications/2/JTEMBHe2005.pdf

Trace elements in agroecosystems and impacts on the environment

China faces great challenges in protecting its soil from contamination caused by rapid industrialization and urbanization over the last three decades. Recent nationwide surveys show that 16% of the soil samples, 19% for the agricultural soils, are contaminated based on China’s soil environmental quality limits, mainly with heavy metals and metalloids. Comparisons with other regions of the world show that the current status of soil contamination, based on the total contaminant concentrations, is not worse in China. However, the concentrations of some heavy metals in Chinese soils appear to be increasing at much greater rates. Exceedance of the contaminant limits in food crops is widespread in some areas, especially southern China, due to elevated inputs of contaminants, acidic nature of the soil and crop species or cultivars prone to heavy metal accumulation. Minimizing the transfer of contaminants from soil to the food chain is a top priority. A number of options are proposed, including identification of the sources of contaminants to agricultural systems, minimization of contaminant inputs, reduction of heavy metal phytoavailability in soil with liming or other immobilizing materials, selection and breeding of low accumulating crop cultivars, adoption of appropriate water and fertilizer management, bioremediation, and change of land use to grow nonfood crops. Implementation of these strategies requires not only technological advances, but also social-economic evaluation and effective enforcement of environmental protection law.

Soil Contamination in China: Current Status and Mitigation Strategies

Heavy metals are natural constituents of the earth's crust, but indiscriminate human activities have drastically altered their geochemical cycles and biochemical balance. This results in accumulation of metals in plant parts having secondary metabolites, which is responsible for a particular pharmacological activity. Prolonged exposure to heavy metals such as cadmium, copper, lead, nickel, and zinc can cause deleterious health effects in humans. Molecular understanding of plant metal accumulation has numerous biotechnological implications also, the long term effects of which might not be yet known.

Heavy metals and living systems: An overview.

Sedum alfredii Hance has been identified as a new zinc (Zn) hyperaccumulating plant species. In this study, the effects of cadmium (Cd) supply levels (control, 12.5, 25, 50, 100, 200, 400, 800 µmol Cd L −1 ) on the growth and cadmium accumulation and Zn supply on Cd accumulation in S. alfredii Hance were studied. The results showed that no reduction in shoot and root dry matter yields were noted when the plants were grown at Cd supply levels up to 200 µmol L −1 in nutrient solution. Slight stimulation on shoot growth was noted at relatively low Cd levels (25 to 100µmol L −1 ). Cadmium concentrations in leaves and stems increased with increasing Cd supply levels, and reached a maximum of approximately 9000 and 6500 mg kg −1 (DW) at 400 µmol Cd L −1 , respectively. Root Cd concentration increased sharply only at relatively high Cd levels. Cadmium distribution in different parts of the

/pdf/cadmium-tolerance-and-hyperaccumulation-in-a-new-zn-2k7g3jtse5.pdf

Cadmium tolerance and hyperaccumulation in a new Zn-hyperaccumulating plant species (Sedum alfredii Hance)

Field survey and greenhouse experiments were carried out to identify and characterize zinc (Zn) uptake and accumulation by a new Zn hyperaccumulating plant species (Sedum alfredii Hance) native to China. Zinc concentration in the shoots ofSedum alfredii Hance grown on an ancient mined area ranged from 4134 to 5000 mg/kg, with a mean of 4515 mg/kg. It suggests thatSedum alfredii could not only grow on heavily Pb/Zn contaminated soils, but also could accumulate extraordinarily high concentration of Zn. Under nutrient solution culture conditions,Sedum alfredii Hance grew healthy at Zn supplying levels from 0.006 to 240 mg · L−1. Zinc concentration in the shoots increased with external Zn levels increasing. The Zn concentration and accumulation in the shoots reached the highest at Zn supply level of 80 mg/L, with 19.67 g/kg and 19.83 mg/plant, respectively. All the results showed thatSedum alfredii Hance is a new Zn hyperaccumulating plant. This provides a new plant material to explore mechanism of plant to hyperaccumulate Zn, and a potent new plant species to phytoremediate Zn contaminated soils.

Sedum alfredii H: A new Zn hyperaccumulating plant first found in China

Copper pollution in soils is widespread, and its accumulation in crop products could pose a risk on human health. In this paper, bioavailability of added copper (Cu) and critical Cu concentrations in a vegetable garden soil was evaluated for Chinese cabbage (Brassica chinensis L.), pakchoi (Brassica chinensis L.), and celery (Apiumg graveolens L. var. dulce DC) based on human dietary toxicity. The availability of added Cu in the soil decreased with incubation time, and had minimal change after 10–12 weeks. After incubated for 12 weeks, about 60% of added Cu was not extractable by DTPA. The same crops were also grown in sand culture to determine their responses to solution Cu. Shoot growth was significantly inhibited at Cu concentrations above 10 mg kg−1 in the solution or above 150 mg kg−1 (DTPA-Cu) in the soil. The sensitivity of the crops to Cu toxicity differed among the three vegetable crops. Copper concentration in shoots and edible parts varied with Cu supply levels and type of the vegetables. Negat...

Assessing copper thresholds for phytotoxicity and potential dietary toxicity in selected vegetable crops.

Sedum alfredii Hance has been identified to be a zinc (Zn) hyperaccumulating plant species native to China. In this study, growth responses, uptake and accumulation of cadmium (Cd) and Zn by S. alfredii were examined at Cd/Zn combining supply levels. The results showed that optimal growth for both shoots and roots was found when the plant grew at the Cd/Zn level of 100/500 μmol L−1. The concentrations of Cd and Zn in leaves and Sstems of Sedum afredii H increased with increasing Cd and Zn supply levels. The distributions of the metals in different plant parts decreased in the order: stem > leaf  ≫  root for Zn and leaf  > stem ≫ root for Cd. The highest concentrations of Zn (23.2 mg g−1) in the stems and Cd (12.1 mg g−1) in the leaves were noticed when the plants were grown at the Zn/Cd levels of 1000/50 and 500/400 μmol L−1, respectively. The maximum Cd and Zn accumulations in the shoots were 5.1 and 11.2 mg plant−1 at the Cd/ Zn combining levels of 400/250 and 100/500 μmol L−1, respectively. Zi...

Uptake and Accumulation of Cadmium and Zinc by Sedum Alfredii Hance at Different Cd/Zn Supply Levels

Sedum alfredii Hance has been identified as a Zn-hyperaccumulating plant species native to China. The characteristics of Zn uptake and accumulation in the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii were investigated under nutrient solution and soil culture conditions. The growth of HE was normal up to 1000 μM Zn in nutrient solution, and 1600 mg Zn kg−1 soil in a Zn-amended soil. Growth of the NHE was inhibited at Zn levels ≥250 μM in nutrient solution. Zinc concentrations in the leaves and stems increased with increasing Zn supply levels, peaking at 500 and 250 μM Zn in nutrient solution for the HE and the NHE, respectively, and then gradually decreased or leveled off with further increase in solution Zn. Minimal increases in root Zn were noted at Zn levels up to 50 μM; root Zn sharply increased at higher Zn supply. The maximum Zn concentration in the shoots of the HE reached 20,000 and 29,000 mg kg−1 in the nutrient solution and soil experiments, respectively, approximately 20 times greater than those of the NHE. Root Zn concentrations were higher in the NHE than in the HE when plants were grown at Zn levels ≥50 μM. The time-course of Zn uptake and accumulation exhibited a hyperbolic saturation curve: a rapid linear increase during the first 6 days in the long-term and 60 min in the short-term studies; followed by a slower increase or leveling off with time. More than 80% of Zn accumulated in the shoots of the HE at half time (day 16) of the long-term uptake in 500 μM Zn, and also at half time (120 min) of the short-term uptake in 10 μM 65Zn2+. These results indicate that Zn uptake and accumulation in the shoots of S. alfredii exhibited a down-regulation by internal Zn accumulated in roots or leaves under both nutrient solution and soil conditions. An altered Zn transport system and increased metal sequestration capacity in the shoot tissues, especially in the stems, may be the factors that allow increased Zn accumulation in the hyperaccumulating ecotype of S. alfredii.

http://www.irrec.ifas.ufl.edu/IRSWS/History%20Publications/1/PSYang2006.pdf

Xin-xian Long

Papers

Cadmium tolerance and hyperaccumulation in a new Zn-hyperaccumulating plant species (Sedum alfredii Hance)

Sedum alfredii H: A new Zn hyperaccumulating plant first found in China

Assessing copper thresholds for phytotoxicity and potential dietary toxicity in selected vegetable crops.

Uptake and Accumulation of Cadmium and Zinc by Sedum Alfredii Hance at Different Cd/Zn Supply Levels

Dynamics of zinc uptake and accumulation in the hyperaccumulating and non-hyperaccumulating ecotypes of Sedum alfredii Hance