Roles of apoplastic peroxidases, laccases, and lignification in the manganese tolerance of hyperaccumulator Phytolacca americana

Abstract

We investigated the response of Mn-hyperaccumulator Phytolacca americana L. to manganese excess as well as the relationships between lignin deposition in the plant's leaves, peroxidase and laccase activities in the leaf apoplast, and Mn toxicity. The exceptionally high tolerance of P. americana to Mn, both in solution and in tissue, was confirmed. No visible brown spot was observed in the leaves of plants treated with B10,000 lM Mn for 10 days. Mn treatment significantly increased lignin content and laccase activity in the apoplastic washing fluid (AWF) of P. americana leaves. In contrast, an increase in the Mn supply was paralleled by a significant decrease in the concentration of total phenolic compounds (TPCs) and in water-soluble guaiacol peroxidase (SPOD) activity in leaf AWF. This result suggested that an increase in lignin deposition decreased the concentration of apoplastic TPCs that are available to generate potentially toxic intermediates by acting as peroxidase substrates. Thus, data of the present study indicate that lignin formation by laccase activities reduces Mn toxicity and increases Mn tolerance of P. americana by depressing SPOD-mediated formation of toxic intermediates from TPCs.

De novo Assembly of the Pokeweed Genome Provides Insight Into Pokeweed Antiviral Protein (PAP) Gene Expression

“…A laccase was shown to mediate broad-spectrum pathogen resistance in cotton by integrating the phenylpropanoid pathway, JA biosynthesis, and balance of JA-SA defense responses (Hu et al, 2018). In pokeweed, an increase in laccase activity during Mn treatment is thought to contribute to heavy metal tolerance by reducing the level of toxic reactive oxygen species (Gao et al, 2012). Also present in this cluster were fasciclin-like arabinogalactan proteins (FLAs).…”

Effects of mechanical stressors caused by mean flow and turbulence on aquatic plants with different morphologies

“…Additionally, ROS production and the lignification of cell walls are closely associated in plants. With the availability of H 2 O 2 as an oxidant, PODs generate monolignol phenoxy radicals that couple spontaneously to form lignin polymers (Gao, Peng, Chen, Wang, & Shen, ; Passardi, Penel, & Dunand, ). In this study, the plants in the high turbulence treatments exhibited high levels of lignin production compared with plants in mean flow and stagnant water.…”

Lignins: Biosynthesis and Biological Functions in Plants

“…Another study showed that Al can induce the expression of the enzyme genes in the lignin biosynthesis pathway, the expression of 4CL , CAD , C3H and PAL genes were increased under Al stress [ 100 ]. Other heavy metals such as copper (Cu), cadmium (Cd), zinc (Zn) and manganese (Mn) stress can also increase lignin content in some plants [ 76 , 96 , 101 , 102 , 103 , 104 ]. Increasing of Cu concentration in the culture medium enhanced the activity of PAL, CAD, caffeic acid POD, the accumulation of phenolic compounds and lignin in the suspension cells of ginseng root [ 105 ].…”

“…The results indicated lignin biosynthesis was crucial for the hyperaccumulation of Zn/Cd in Thlaspi caerulescens and it might be related to ion absorption and transport. Our previous study found that the deposition of lignin reduced the toxic effects of Mn, which is an important mechanism of manganese tolerance in a Mn-hyperaccumulator Phytolacca americana [ 101 ]. Lignification of xylem in roots can reduce the transport of Cd to the shoots [ 110 ].…”