Dual Role of Metallic Trace Elements in Stress Biology—From Negative to Beneficial Impact on Plants

Abstract

Heavy metals are an interesting group of trace elements (TEs). Some of them are minutely required for normal plant growth and development, while others have unknown biological actions. They may cause injury when they are applied in an elevated concentration, regardless of the importance for the plant functioning. On the other hand, their application may help to alleviate various abiotic stresses. In this review, both the deleterious and beneficial effects of metallic trace elements from their uptake by roots and leaves, through toxicity, up to the regulation of physiological and molecular mechanisms that are associated with plant protection against stress conditions have been briefly discussed. We have highlighted the involvement of metallic ions in mitigating oxidative stress by the activation of various antioxidant enzymes and emphasized the phenomenon of low-dose stimulation that is caused by non-essential, potentially poisonous elements called hormesis, which is recently one of the most studied issues. Finally, we have described the evolutionary consequences of long-term exposure to metallic elements, resulting in the development of unique assemblages of vegetation, classified as metallophytes, which constitute excellent model systems for research on metal accumulation and tolerance. Taken together, the paper can provide a novel insight into the toxicity concept, since both dose- and genotype-dependent response to the presence of metallic trace elements has been comprehensively explained.

Yield, Essential Oil and Quality Performances of Artemisia dracunculus, Hyssopus officinalis and Lavandula angustifolia as Affected by Arbuscular Mycorrhizal Fungi under Organic Management

“…In this research, the increase of Zn content was recorded only in tarragon and lavender treated with AMF. A recent investigation of Muszýnska and Labudda [43] showed the ability of Zn to enhance plant tolerance to abiotic stress, which may be partially connected with the increase in stress tolerance of AMF-treated A. dracunculus compared to L. angustifolia and H. officinalis in the present investigation. Interestingly, the concentration of two other natural antioxidants, such as iodine and selenium, significantly increased in AMF-inoculated A. dracunculus plants, showing the highest tolerance to abiotic stress as shown by biochemical analysis ( Table 5).…”

Hormesis in Plants: The Role of Oxidative Stress, Auxins and Photosynthesis in Corn Treated with Cd or Pb

“…Ban et al [68] showed that a low dose of Pb stimulated growth, the photosynthetic rate, transpiration and stomatal conductance in corn. In the shoots of many plant species, the hormesis that is caused by Cd is associated with an increase in the photosynthesis activity, which improves plant development [4,41]. In our study, the hormetic stimulation of growth that was caused by Pb was correlated with increased photosynthetic and transpiration rates, while the hormetic stimulation of growth that was caused by Cd led to a significant decrease of all of the investigated plant gas exchange parameters (Figure 7).…”

“…We would like to stress that an increase in the IAA and flavonol content have been proposed as the key factors in hormesis here for the first time. In general, the literature on metals and hormesis is dominated by studies on the role of oxidative stress and phytohormones such as abscisic acid, ethylene or jasmonates, with little information on the role of IAA and flavonols [3,4,6,41,54]. The results presented here also suggest that an increase in the photosynthesis and transpiration rates are not necessary for stimulating hormetic growth.…”

“…However, fewer works have addressed the stimulatory effect of sub-toxic levels of HMs-the phenomenon of hormesis. However, hormesis has been gaining more and more interest in recent years [2][3][4]41]. The stimulatory effect of low concentrations of Cd on plant growth was reported for Lonicera japonica by Jia et al [8,42] and for Brassica juncea by Seth et al [43].…”

Novel Segmented Concentration Addition Method to Predict Mixture Hormesis of Chlortetracycline Hydrochloride and Oxytetracycline Hydrochloride to Aliivibrio fischeri

“…We studied the combined effect of 10 ionic liquids (ILs) on luciferase, and observed that their mixtures presented a higher inhibitory effect, when all ILs components were in their maximum stimulatory effect concentration [11]. Therefore, the beneficial effects [12] in hormesis should be evaluated in the context of mixtures.…”