Metal (Pb, Zn and Cu) uptake and tolerance by mangroves in relation to root anatomy and lignification/suberization

Abstract

Metal pollution has been widely reported in mangrove wetlands; however, the mechanisms involved in metal detoxification by mangroves are still poorly understood. This study aimed to investigate the possible function of root anatomy and lignification/suberization on metal uptake and tolerance in seedlings of six species of mangroves. The results revealed that the three rhizophoraceous species (Bruguiera gymnorrhiza (L.) Poir, Kandelia obovata Sheue, Liu & Yong and Rhizophora stylosa Griff) consistently exhibited higher metal tolerances than the three pioneer species (Aegiceras corniculatum (Linn.) Blanco, Acanthus ilicifolius L. and Avicennia marina (Forsk.) Viern.). Moreover, metal-tolerant species often exhibited a thick exodermis with high lignification and suberization. The tolerance indices of the mangroves were found to be positively correlated with the amounts of lignin and suberin deposition within the exodermal cell walls. The observed metal uptake by the excised roots further illustrated that a lignified/suberized exodermis directly delayed the entry of metals into the roots, and thereby contributed to a higher tolerance to heavy metals. In summary, the present study proposes a barrier property of the lignified/suberized exodermis in dealing with the stresses of heavy metals, such that the mangroves which possessed more extensive lignification/suberization within the exodermis appeared to exhibit higher metal tolerance.

The Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Alleviates Salinity Stress in Cassava

“…In contrast, 28.3% of SAHA-upregulated genes are high salinity stress-responsive (Figure S2A), and only 27 SAHA-upregulated genes were upregulated by high-salinity stress (2 and/or 24 h NaCl treatment; Table 6). In mangrove plants, lignin accumulation functions in blocking metal-ion influx with higher suberization, suggesting that lignification can prohibit ions from flowing inside (Cheng et al, 2014). We analyzed the following three genes that are believed to play critical roles in regulating lignin accumulation: L-phenylalanine ammonia lyase ( PAL ), cinnamyl alcohol dehydrogenase ( CAD ), and caffeic acid 3-Omethyltransferase ( COMT ) genes (Whetten and Sederoff, 1995; Ma and Xu, 2008; Nguyen et al, 2016).…”

Physiological and molecular mechanisms of heavy metal accumulation in nonmycorrhizal versus mycorrhizal plants

“…HM ions can bind to the functional groups of cell wall components, such as cellulose, hemicellulose, lignin, and pectin (Chen, Liu, Wang, Zhang, & Owens, ; Parrotta, Guerriero, Sergeant, Cai, & Hausman, ). Some plants can enhance their lignin biosynthesis in response to HM exposure, thereby suggesting that lignin in plant cell walls plays a role in sequestering HMs (Cheng et al, ; Elobeid, Gobel, Feussner, & Polle, ). By HM sequestration in root cell walls, the entry of HMs into the protoplasts can be reduced, thereby alleviating the toxicity of HMs in plant cells.…”

Mangrove root: adaptations and ecological importance

“…Keshavarz et al (2012) revealed that the Cd and V were negligible in sediments surrounding roots zones of A. marina and R. mucronata, whereas Pd concentrations were higher compared to leaves and roots. Cheng et al (2014) revealed that the three rhizophoraceous species (B. gymnorrhiza (L.) Poir, K. obovata Sheue, Liu and Yong, and R. stylosa (Griff) consistently exhibited higher metal (Pb, Zn and Cu) tolerances than the three pioneer species [Aegiceras corniculatum (Linn.) Blanco, Acanthus ilicifolius L. and A. marina (Forsk)].…”