Plant Responses to Heavy Metal Toxicity

Abstract

Plants, like all other organisms, have evolved different mechanisms to maintain physiological concentrations of essential metal ions and to minimize exposure to non-essential heavy metals. Some mechanisms are ubiquitous because they are also required for general metal homeostasis, and they minimize the damage caused by high concentrations of heavy metals in plants by detoxification, thereby conferring tolerance to heavy metal stress. Other mechanisms target individual metal ions (indeed some plants have more than one mechanism to prevent the accumulation of specific metals) and these processes may involve the exclusion of particular metals from the intracellular environment or the sequestration of toxic ions within compartments to isolate them from sensitive cellular components. As a first line of defense, many plants exposed to toxic concentrations of metal ions attempt to prevent or reduce uptake into root cells by restricting metal ions to the apoplast, binding them to the cell wall or to cellular exudates, or by inhibiting long distance transport. If this fails, metals already in the cell are addressed using a range of storage and detoxification strategies, including metal transport, chelation, trafficking, and sequestration into the vacuole. When these options are exhausted, plants activate oxidative stress defense mechanisms and the synthesis of stress-related proteins and signaling molecules, such as heat shock proteins, hormones, and reactive oxygen species.

Nutritional and biochemical changes induced by lead in sunflower (Helianthus annuus L.)

“…Chelating agents contribute to detoxification and increase plant tolerance to toxic levels of metal ions (GASIC; KORBAN, 2006), and it is already well established that amino acids can be mobilized in response to Pb toxicity to form complexes with this metal (MAESTRI et al, 2010;MANARA, 2012;POURRUT et al, 2011).…”

“…Considering that roots are directly exposed to the contaminant, it is likely that this increase is the result of the induction of stress proteins (LAMHAMDI et al, 2010). In this context, metallothioneins and phytochelatins represent the main classes of heavy metal-chelating peptides in plants (MANARA, 2012;POURRUT et al, 2011). Pb stress has also been shown to increase the protein content, including phytochelatins, in Ceratophyllum demersum L. (MISHRA et al, 2006).…”

Accumulation of nickel in transgenic tobacco

“…Therefore T(1)24C is potential to be used on soil contaminated with higher level of Ni for phytoremediation purposes. The accumulation of Ni in the roots of T(1)24C (TABLE (1)) was also among the highest Ni accumulation in the roots of nineteen wetland plant species assessed by [3]. The accumulation of Ni in T(1)24C was less than the Ni accumulation was shown by Alternanthera philoxeroides (293.2 ± 31.4) that was found in research done by [3].…”

“…Nitric Acid (HNO 3 ) 65% was added to the samples according to ratio 1 g sample to 20 mL HNO 3 . The mixtures were left overnight at room temperature and were then heated on a hot plate at 115 °C for 1-2 hours.…”

The Growth and Antioxidative Responses of Sonchus oleraceus (Linnaeus, 1753) Under Cu(II), Pb(II), Cd(II) and Cr(VI) Stress Condition

“…Cu were exposed for 30 days not affect the morphological appearance of S. oleraceus. This is possible because Cu including essential metals (micronutrients) needed by plants in the process of metabolism, in addition to the translocation of Cu from root to stem relatively low [21]. Pb causes the S. oleraceus leaves are green-yellowish, the same result is also shown Eichornia crassipes leaves exposed metal Pb [22].…”