Main Article Content
Heavy metal contamination is one of the serious environmental problems. Among heavy metals, lead (Pb) is a non-essential metal with highly toxic to plants and animals. Due to the high atomic weight, Pb is largely accumulated in plant roots more than shoots. Pb absorbed along with water and other nutrient possibly pass through cell wall and cell membrane. A number of plants have been accumulated Pb in their cell wall and intercellular space. This review paper focuses on the role of plant cell wall as the first line protection of the plant cells against Pb toxicity. Upon Pb exposure, production of Reactive Oxygen Species (ROS) such as nitric oxide (NO) and hydrogen peroxide (H2O2) have been increased. These small molecules are normally used as signaling molecules in antioxidation system activating radical scavengers e.g. peroxidase and catalase. Sharply increased ROS may also acts as a signal for remodifying cell wall structure. Pectins and other polysaccharides in plant cells can bind and sequester Pb within the cell walls. The thick cell walls act as a barrier that limit Pb from entering into the protoplasm as well as serving as a compartment for storing the metal.
 S. K. Marx, S. Rashid, and N. Stromsoe, “Globalscale patterns in anthropogenic Pb contamination reconstructed from natural archives,” Environmental Pollution, vol. 213, pp. 283–298, 2016.
 H. B. Bradl, “Adsorption of heavy metal ions on soils and soils constituents,” Journal of Colloid and Interface Science, vol. 277, pp. 1–18, 2004.
 J. Somasundaram, R. Krishnasamy, S. Mahimairaja, and P. Savithri, “Dynamics of lead (Pb) in different soil conditions,” Journal of Environmental Science & Engineering, vol. 48, no. 2, pp. 123–128, 2006.
 J. Nduka and O. Orisakwe, “Assessment of environmental distribution of lead in some municipalities of South-Eastern Nigeria,” International Journal of Environmental Research and Public Health, vol. 7, no. 6, pp. 2501–2513, 2010.
 C. A. de Abreu, M. F. de Abreu, and J. C. de Andrade, “Distribution of lead in the soil profile evaluated by DTPA and Mehlich-3 solutions,” Bragantia, vol. 57, pp. 185–192, 1998.
 ATSDR. (2017). Case studies in environmental medicine: Lead toxicity. U.S. Department of Health and Human Services [Online]. Available: https://www.atsdr.cdc.gov/csem/lead/docs/lead.pdf
 P. Sharma and R. S. Dubey, “Lead toxcity in plants,” Brazilian Journal of Plant Physiology, vol. 17, no. 1, pp. 35–52, 2005.
 I. Seregin and V. Ivaniov, “Physiological aspects of cadmium and lead toxicty effects on higher plants,” Russian Journal of Plant Physiology, vol. 48, pp. 606–630, 2001.
 M. Fahr, L. Laplaze, N. Bendaou, V. Hocher, M. E. Mzibri, D. Bogusz, and A. Smoni, “Effect of lead on root growth,” Frontiers in Plant Science, vol. 4, pp. 1–7, 2013.
 N. Rascio and F. Navari-Izzo, “Heavy metal hyperaccumulating plants: How and why do they do it? And what makes them so interesting?,” Plant Science, vol. 180, pp. 169–181, 2011.
 L. Q. Alves, R. M. de Jesus, A. A de Almeida, V. L. Souza, and P. A. Mangabeira, “Effects of lead on anatomy, ultrastructure and concentration of nutrients in plants Oxycaryum cubense (Poep. & Kunth) Palla: A species with phytoremediator potential in contaminated watersheds,” Environmental Science and Pollution Research, vol. 21, no. 10, pp. 6558–6570, 2014.
 L. Zheng, T. Peer, V. Seybold, and U. Lütz-Meindl, “Pb-induced ultrastructural alterations and subcellular localization of Pb in two species of Lespedeza by TEM-coupled electron energy loss spectroscopy,” Environmental and Experimental Botany, vol. 77, pp. 196–206, 2012.
 N. Aggangan, N.Cadiz, A. Llamado, and A. Raymundo, “Jatropha curcas for bioenergy and bioremediation in mine tailing area in Mogpog, Marinduque, Philippines,” Energy Procedia, vol. 110, pp. 471–478, 2017.
 S. S. Dhiman, C. Selvaraj, J. Li, R. Singh, X. Zhao, D. Kim, J. Y. Kim, Y. C. Kang, and J. K. Lee, “Phytoremediation of metal-contaminated soils by the hyperaccumulator canola (Brassica napus L.) and the use of its biomass for ethanol production,” Fuel, vol. 183, pp. 107–114, 2016.
 K. Chandra Sekhar, C. T. Kamala, N. S. Chary, V. Balaram, and G. Garcia, “Potential of Hemidesmus indicus for phytoextraction of lead from industrially contaminated soils,” Chemosphere, vol. 58, no. 4, pp. 507–514, 2005.
 J. Yang, G. Zheng, J. Yang, X. Wan, B. Song, W. Cai, and J. Guo, “Phytoaccumulation of heavy metals (Pb, Zn, and Cd) by 10 wetland plant species under different hydrological regimes,” Ecological Engineering, vol. 107, pp. 56–64, 2017.
 D. J. Cosgrove and M. C. Jarvis, “Comparative structure and biomechanics of plant primary and secondary cell walls,” Frontiers in Plant Science, vol. 3, no. 204, pp. 1–6, 2012.
 D. J. Cosgrove, “Growth of the plant cell wall,” Nature Reviews Molecular Cell Biology, vol. 6, no. 11, pp. 850–861, 2005.
 L. M. Casano, M. R. Braga, R. Álvarez, M. Eva, and E. Barreno, “Differences in the cell walls and extracellular polymers of the two Trebouxia microalgae coexisting in the lichen Ramalina farinacea are consistent with their distinct capacity to immobilize extracellular Pb,” Plant Science, vol. 236, pp. 195–204, 2015.
 H. Inoue, D. Fukuoka, Y. Tatai, H. Kamachi, M. Hayatsu, M. Ono, and S. Suzuki, “Properties of lead deposits in cell walls of radish (Raphanus sativus) roots,” Journal of Plant Research, vol. 126, pp. 51–61, 2013.
 I. Rabeda, H. Bilski, E. J. Mellerowicz, A. Napieralska, S. Suski, A. Wozny, and M. Krzeslowska, “Colocalization of low-methylesterified pectins and Pb deposits in the apoplast of aspen roots exposed to lead,” Environmental Pollution, vol. 205, pp. 315–326, 2015.
 M. Krzesłowska, I. Rabeda, A. Basinska, M. Lewandowski, E. J. Mellerowicz, A. Napieralska, S. Samardakiewicz, and A. Wozny, “Pectinous cell wall thickenings formation - A common defense strategy of plants to cope with Pb,” Environmental Pollution, vol. 214, pp. 354–361, 2016.
 M. Krzesłowska, “The cell wall in plant cell response to trace metals: Polysaccharide remodeling and its role in defense strategy,” Acta Physiol Plant, vol. 33, pp. 35–51, 2011.
 M. Wierzbicka, “Lead in the apoplast of Allium cepa L. root tips — ultrastructural studies,” Plant Science, vol. 133, pp. 105–119, 1998.
 M. Krzesłowska, M. Lenartowska, S. Samardakiewicz, H. Bilski, and A. Woźny, “Lead deposited in the cell wall of Funaria hygrometrica protonemata is not stable-a remobilization can occur,” Environmental Pollution, vol. 158, no. 1, pp. 325–338, 2010.
 L. Parrotta, G. Guerriero, K. Sergeant, G. Cai, and J. F. Hausman, “Target or barrier? the cell wall of early- and later-diverging plants vs cadmium toxicity: Differences in the response mechanisms,” Frontiers in Plant Science, vol. 6, pp. 1–16, 2015.
 N. Rascio and F. Navari-Izzo, “Heavy metal hyperaccumulating plants: How and why do they do it? and what makes them so interesting?” Plant Science, vol. 180, pp. 169–181, 2011.
 Z. B. Luo, J. He, A. Polle, and H. Rennenberg, “Heavy metal accumulation and signal transduction in herbaceous and woody plants: Paving the way for enhancing phytoremediation efficiency,” Biotechnology Advances, vol. 34, pp. 1131–1148, 2016.
 S. Verma and R. S. Dubey, “Lead toxicity induces lipid peroxidation and alters the activities of antioxidant enzymes in growing rice plants,” Plant Science, vol. 164, pp. 645–655, 2003.
 S. Zafari, M. Sharifi, L. A. J. Mur, and N. A. Chashmi, “Favouring NO over H2O2 production will increase Pb tolerance in Prosopis farcta via altered primary metabolism,” Ecotoxicology and Environmental Safety, vol. 142, pp. 293–302, 2017.
 S. S. Sharma and K. J. Dietz, “The relationship between metal toxicity and cellular redox imbalance,” Trends Plant Science, vol. 14, no. 1, pp. 43–50, 2009.
 A. Piotrowska-Niczyporuk, A. Bajguz, E. Zambrzycka, and B. Godlewska-z̈yłkiewicz, “Phytohormones as regulators of heavy metal biosorption and toxicity in green alga Chlorella vulgaris (Chlorophyceae),” Plant Physiology and Biochemistry, vol. 52, pp. 52–65, 2012.
 S. K. Kaur Kohli, N. Handa, S. Bali, S. Arora, A. Sharma, R. Kaur, and R. Bhardwaj, “Modulation of antioxidative defense expression and osmolyte content by co-application of 24-epibrassinolide and salicylic acid in Pb exposed Indian mustard plants,” Ecotoxicology and Environmental Safety, vol. 147, pp. 382–393, 2018.
 R. Tenhaken, “Cell wall remodeling under abiotic stress,” Frontiers in Plant Science, vol. 5, pp. 1–9, Jan. 2015.