Written by Emin Yasul
Metals with high densities or atomic weights are named heavy metals. Although heavy metals are contained in the soil naturally, geologic activities increase the concentration of the heavy metals to amounts that are harmful to plants. At higher levels, heavy metals have the skills to produce toxic effects in plants; therefore, plant cells control their usage and uptake.
Agricultural lands in many regions of the world are slightly to moderately contaminated by heavy metal toxicity for example Cu, Zn, Ni, Cr, and Pb. The reason could be the long-term use of phosphatic stuff, industrial waste, and bad watering in agricultural soils. The first reflex of plants is the production of reactive oxygen species (ROS) when exposed to high levels of heavy metals.
The toxic effects of metals on plants, influence them negatively, for example, decreasing uptake levels of nutrients and water, thus inhibiting plant growth.
Plants have defense tactics against heavy metals. The first defense tactic is activating antioxidants such as POD, SOD, APX, CAT, GR, ASA, and GSH. The second defense tactic is to activate their root exudates and cell walls. (1)
Chromium Toxicity in Plants
This kind of toxicity reduces seed sodding, decreasing plant growth level day by day, and badly influences photosynthetic behavior. (1)
Arsenic and Mercury Toxicity in Plants
Arsenic and mercury are in the “top 5 most dangerous” among pollutants. There are a lot of suggestions for solutions to arsenic and mercury toxicity but because of time issues, economic issues, and practical issues, none of them seems unrealistic. (1)
Silver and Lead Toxicity in Plants
Al and Pb have bad influences on the production of ATP, germination, root and plant growth, and chlorophyll production. Also, these heavy metals are damaging DNA and ROS. In recent years ultrasonic cures have been one of the most potent solutions against Al and Pb toxicity. (1)
Se (Selenium) is an element that has reducing effects against heavy metal toxicity in plants. Researchers have proven that Se has positive effects on plant growth in plants under metal stress. (1)
Copper Toxicity in Plants
Copper is an element that is a micronutrient for plants. Also copper has a big role in CO2 assimilation and production of ATP. In recent times, industrial activities have had a bad influence on copper levels in plants. Accordingly, copper levels are increasing in plants. This situation has bad effects on plant growth and plant metabolism. (2)
Cobalt Toxicity in Plants
High cobalt levels disturb the plant body system. The most popular reason for increasing cobalt levels in soil is: burning fossil fuels and spreading sewage sludge and manure. For example, high Co percentages affected the migration of P, S, Mn, Zn, and Cu from the roots to the tops in cauliflower day by day. (2)
Nickel Toxicity in Plants
Mining activities, burning of coal, burning oil, and sewage wastes are the top common reasons for increasing Ni levels in nature, soil, and crop plants. The percentage of Ni levels in polluted soils is more than 20 or 30 times higher than in normal soils. High Ni levels disturb cell membrane activities and nutritional balance. Also, a decrease in uptake levels of water is one of the signs of high Ni levels. (2)
Zinc Toxicity in Plants
Zinc contents in soil naturally and zinc is a compulsory element for plants. Because plants have to use zinc for metabolic activities and body growth. However unsuitable zinc levels trigger low photosynthetic speed, low body growth speed low respiratory, unbalanced mineral usage, and an increase in the production of reactive oxygen. Forest fires, volcanos, mining activities, sewage waste, and phosphate fertilizers due to high zinc levels in nature and soil. (5)
References:
1. Basharat Ali, & Rafacat A. Gill. (2022, October 21). Editorial: Heavy metal toxicity in plants: Recent insights on physiological and molecular aspects, volume II. Frontiers. https://www.frontiersin.org/articles/10.3389/fpls.2022.1016257/full
2. SK Yadav. (n.d.). Just a moment... Just a moment... https://www.sciencedirect.com/science/article/pii/S0254629909003159
3. Paola I. Angulo-Bejarano, Jonathan Puente-Rivera, & Rocio Cruz-Ortega. (2021, March 27). Metal and metalloid toxicity in plants: An overview on molecular aspects. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8066251/
4. Ilektra Sperdouli. (2022, November 23). Heavy metal toxicity effects on plants. MDPI. https://www.mdpi.com/2305-6304/10/12/715
5. Harmanjit Kaur, & Neera Garg. (2021, May 21). Zn toxicity in plants. PubMed. https://pubmed.ncbi.nlm.nih.gov/34043068/
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