**6. Conclusion**

Soudek et al. (2010) treated linen (*Linum usitatissimum* L.) seeds with different concentrations of lead, nickel, copper, zinc, cadmium, cobalt, arsenic, and chromium heavy metals and reported that heavy metal stress had negative effects on the number of germinating seeds and seedling root development. The negative effect of heavy metal stress on root length in plants may result from the division of cells in the root region or the prolongation of the cell cycle [31]. The root, stem, and leaf structures of the runner bean and artichoke seedlings grown in high Cu and Pb concentrations (160, 320, 640, 1280 ppm) examined in this study were degraded as a result of oxidative damage. Therefore, the epidermal cells forming the surface of these parts were damaged, which negatively affected root, stem, and leaf growth. However, it also caused adverse conditions such as dryness, shrinkage, and necrosis in the leaves although Cu and Pb heavy metals applied at low concentrations generally stimulated growth and increase the number of leaves in the plant [39, 47]. Furthermore, browning caused by heavy metal stress was observed in the roots of the runner bean and artichoke seedlings in which high concentrations of heavy metals were applied. This color change occurs with the increase in the amount of suberin in stem cells. Therefore, suberin stem cells will limit the uptake of water,

The defense mechanisms developed by plants against heavy metal stress may vary in the level of family, genus, species, subspecies, and variety [54–57]. The defense mechanisms that allow plants to be tolerant to heavy metals have not yet been fully understood. However, the mechanisms of tolerance include vacuolar phenomena [58], enzymatic and nonenzymatic antioxidant systems [59, 60], metal-binding ligands such as metallothionein [61], and alternative oxidase pathways [62].

Although copper is an essential element, it is more toxic when it is present in high doses compared to cadmium, a nonessential element. This is explained by the direct influence of copper on the formation of reactive oxygen species [superoxide radical (O2˙), hydrogen peroxide (H2O2), hydroxyl radical (OH)] because it is a

trace element. Since copper and iron transition metals are involved in

oxidoreduction reactions, they act as catalysts that accelerate the formation of reactive oxygen species [63–66]. As in previous studies, it was found that artichoke seedlings are negatively affected mostly by copper in molecular terms [39, 41, 67, 68]. The highest negative effect was observed in groups subjected to copper solutions in terms of root length, root dry weight, total soluble protein amount, and

Reactions to heavy metal stress in this study emerged as different anatomical results in both plants. However, it can be determined that the response of coppertreated samples was not always greater than that of the lead-treated samples even though they responded differently to different concentrations in terms of anatomical results. Previously the effect rate observed at the molecular level in Cu-treated samples has been found to be higher than the effect rate in Pb-treated samples in both plants [39–42]. However, it was not the case for the present anatomical study because the roots and stems of the plants were examined in terms of many param-

It was observed that seedlings belonging to runner bean species showed high tolerance against lead and copper stress. The genome of the plants was preserved at 94–95%, and no significant reduction in total soluble protein was observed especially at 1280 ppm concentration of lead and copper solutions. This situation has led to the conclusion that runner bean species has a strong defense mechanism against heavy metal contamination [40–42, 49]. In this anatomically based study, it would be wrong to say that one heavy metal is always superior to another in terms of its effects because plant parts were examined anatomically in terms of many parameters and similar results were not observed in all. The reaction of the plants as

eters, so heavy metals did not show the same effect [47] (**Figures 17**–**25**).

and plant growth inhibition occurs [61, 62].

*Plant Communities and Their Environment*

genomic mold stability [39–42] (**Figures 17**–**22**).

**18**

It is the fact that the application of some materials which are not used consciously or at the recommended dosage and which contain heavy metals in order for the crop to be attractive for the consumers actually yields negative results. Therefore, this study is important about examining the extent of heavy metal phytotoxic effects related determining them on plants phenological development in the point of morphologically and anatomically changes. The information given in this study is valuable as it presents the negative molecular effect of heavy metal pollution on the plant in terms of morphological and anatomical aspects. Furthermore, this study will guide the researchers on the effects of environmental pollution in relation with the phenological development of economic plants and hence on human health.

Heavy metal and nanoparticule-nanotube-induced plants must be evaluated in the point of biochemistry and examined via scanning electron microscope (SEM) and transmission electron microscope (TEM) regarding their root, stem, and leaf structure and apical tip, leaf-bud primordiums, and provascular tissue in detailed ways for interdisciplinary studies according to plants' phenological development progress.

## **Acknowledgements**

I would like to thank Manisa Celal Bayar University (Turkey) Scientific Research Projects Coordination Unit (BAP) for supporting most of this study as part of the projects numbered 2012-057 and 2014-120.

I am also thankful to Dr. Qi Lu, a member of the Department of Physics and Engineering, and Dr. Gulnihal Ozbay, a member of the Department of Agriculture and Natural Resources at Delaware State University (USA), for the support of some laboratory studies related to nanoparticles and nanotubes.

*Plant Communities and Their Environment*

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