Most sites contaminated with heavy metals, often have a diverse flora tolerant apparently well high levels of metals. The phytorehabilitation is based on the use of plants for the remediation of contaminated sites. It is defined as the use of plants to remove or render less mobile and less toxic environmental contaminants. These techniques are not very aggressive to the environment and relatively inexpensive. They can be applied to organic or inorganic pollutants.

Among these techniques, the phytoextraction relates to mainly the metals absorption of the ground with the plants. The ideal plant for the phytoextraction must be able to accumulate and tolerate strong contents of metals: they are plants known as accumulator or hyper accumulator. The phytoextraction term relates to mainly the absorption of the ground metals with the plants. The plants can accumulate metals, such as: Fe, Mn, Zn, Cu, Mg, Mo, necessary to their good development, but are also able to accumulate metals, such as: Cd, Cr, Pb, Co, Ag, Hg. The tolerance and this bioaccumulation are made possible by an adaptation of the plant, with the introduction of new cellular level of physiological capacities [1] [2] . The best plant for the phytoextraction must be able to accumulate and tolerate strong contents of metals in its parts ready for harvesting, while having a rapid grow- th and a strong biomass [3] . Certain plants are naturally able to accumulate strong contents of metals, they are accumulating plants, the accumulated contents are higher than those present in the ground. Some are known as hyper accumulator, if they are able to accumulate more than 10,000 mg∙kg⁻¹ of Mn or Zn, more than 1000 mg∙kg⁻¹ of Cu, Co, Ni, Pb, Cr, or more than 50 mg∙kg⁻¹ of Cd in their leaves. Unfortunately, although there exists more than 400 listed plant species metal hyper accumulator heavy, they are generally with slow growth and a weak production of biomass; moreover, most of them are found exclusively in tropical regions, and more than 80% are hyper accumulator as the nickel [4] [5] . This strategy of phytoextraction depends on the plant used, that is to say, its ability to extraction, accumulation, translocation (transfer of the pollutant of the roots towards the leaves) as well as to resist strong contents of metals. Most known growth on soil contains strong contents of metals. The present study aims to investigate the effects of the presence of heavy metals (cadmium and zinc) on the growth of barley cultivated in a ground contaminated artificially by these two metals at various concentrations, the growth parameters which we followed are the biomass of the plant and the length of roots and leaves. We also studied the capacities of phytoextraction by barley (Hordium vulgare) that is to say it’s the capacity of extraction, accumulation and translocution, we determined the bioaccumulation factor and the translocution factor.

The effect of heavy metals on plant growth, especially root growth has been reported by several authors [7] -[10] .

Some studies were based on the determination of the biomass of the roots and leaves of biomass to evaluate the toxicity of the metal in plants. Some authors have reported that root growth is more sensitive than the leaves and thus are based on root length to study the toxicity addition to the effects on the production of root biomass and length, the roots may also respond to metal stress by changes in the pattern of root growth and morphology in the present study we investigated the impact of metals on the length of roots and leaves and the production of

root and aboveground biomass.

The lengths of the roots and leaves are shown in Figure 1 and Figure 2 for cadmium, and Figure 5 and Figure 6 in the zinc, metals reduce the lengths of the roots and leaves, but the most significant reduction in the presence of cadmium and respect the roots as reported by the literature, this reduction increases with the content of cadmium in the soil to reach 23.5% while it is around 9% for zinc. Similar reduction in root size was reported by [11] . A reduction in the size of the sheets was observed for the two metals of approximately 10% zinc and 13% cadmium. Signs of stress of the metal after 30 days of culture appear with more cadmium than zinc. This can be explained by the fact that cadmium is the most toxic heavy metal in the environment and that is to severe

toxicity to organisms [12] [13] , against zinc is an essential trace element for plants, but can be highly toxic when present at a excessive concentration [14] . In our case we went up to 4000 mg/kg soil can be that extending the growing season for signs of stress are observed better.

The biomass of the roots and leaves and total biomass are shown in Figure 3 and Figure 4 for the cadmium, cadmium reduced total plant biomass as heavy metals generally reduce the solids content [15] . The reduction in biomass of leaves and roots, depending on the concentration of cadmium is not significant. The most significant reduction was observed for the barley grown in the contaminated at 500 mg/kg soil, but the reduction of leaf biomass was greater than the root contrary to what was expected. Concerning zinc, biomass and root and leaf total biomass are shown in Figure 7 and Figure 8, there is an increase of the total biomass of the plant by increasing the concentration of zinc in the soil, except for the concentration of 4000 mg/kg or there is a reduction. This time the effects of zinc are not apparent on the growth of barley after 30 days of culture, one might even believe that there is a better growth in the presence of zinc as biomass increases the metal is therefore tolerated by plants at this stage of culture.

Previous studies have shown that plants can suffer toxic effects if the soil reaches a high content of metals or 8 mg/kg for cadmium. The results of this study show that barley has no apparent signs of stress after thirty days of culture, it resisted even at a level of 200 mg/kg of soil. The parameter that has detected a stress due to the presence of cadmium is mainly the reduction of root size. We also note that barley is more tolerant to zinc, we observed no evidence of apparent even at 4000 mg/kg soil stress, and there was even increase the total biomass in the presence of strong zinc concentrations.

The accumulation of metals in the roots is larger than that of the leaves (Table 4 and Table 5). This is in agreement with the results of [16] -[18] which found that in general, the concentration of heavy metals accumulated in plant roots is higher than leaves, with one exception: the EDTA-assisted phytoextraction.

The bioconcentration factor (BF) has been widely used to estimate the potential of plants for phytoremediation [19] [20] . BF is an excellent indicator of the ability of metal accumulation by plants because it takes into account the metal content in the soil. A good accumulator plant should have a BF > 1000. In our case, the maximum BCF roots we obtained are 166.72% to a content of 25 mg/kg for cadmium and 169% to a content of 500 mg/kg of zinc. The results also showed that, FC strongly decreases with the increase of the total metal content in soil (Table 4). This suggests that the capacity for phytoextraction decreases with increasing the concentration of Zn and Cd in the soil. This trend is more acute for Zn due to its higher concentration in the soil as compared to Cd.

These results are in agreement with those reported by other authors [19] , which attribute this tendency to a self-adjusting mechanism of the plant, which limits the transport of heavy metals from the roots, the difficulties for metal uptake by plants suffered grown in contaminated soils. Audet and Charest [21] reported that the response to the decrease in BF values is probably related to increased metabolic cost associated with plant tolerance level of heavy metals, but they stressed that other factors influence the soil their interaction with plants, namely the toxicity of heavy metal poisoning causing plants, change in soil pH, and mineral imbalances must be taken into account. TF can be used to estimate the ability of plants to translocate heavy metals from roots to shoots or their above-ground tissues that are easy to harvest [20] [22] . Metals concentrations in the leaves of barley were much lower than in the roots. Therefore, the translocation factor is too low so the metal remains in the roots it is not transferred to the harvestable parts that are most interesting for phytoextraction, which is typical for non-hyperaccumulor plants [23] .

We cannot thus qualify our species of accumulator plant if it is cultivated in grounds contaminated by cadmium and zinc but its tolerance with these metals causes us to want to increase this accumulation for example using EDTA as chelating soil, knowing that addition of EDTA solution has a favorable effect on the absorption of metals, due to its properties acidification and chelation, it could be an effective amendment to improve the phytoextraction. However, this chelator is known to be persistent in soil due to its low biodegradability, which may pose a risk to the environment from leaching into groundwater. Therefore, studies should be conducted in order to find other natural and synthetic biodegradable chelating agents such as EDTA alternatives agents. And some studies have reported some bacteria able to increase the solubility and mobility of heavy metals [24] -[26] .

It can be concluded from this study that a soil with a diverse flora can be contaminated with heavy metals and the species that grow on the ground floor, just being tolerant species to high concentrations of metals, where the interest should be brought to the soil pollution especially as it often is apparent point in our case. It will obviously not make a difference between the control pot and those contaminated with high concentrations of metals. These plants have a good yet growth contaminated with high levels of zinc and cadmium. We must ensure that contaminated sites are not cultured after decontamination to protect human health.