Team:FAFU-CHINA/Plant

Module 1: Phyto-route

Phytoremediation is the use of plants and associated soil microbes to reduce the concentrations or toxic effects of heavy metals in the environments. It is a relatively recent technology and is perceived as cost-effective, efficient, novel, eco-friendly, and solar-driven technology with good public acceptance. In our project, we have selected hyperaccumulator- Sedum alfredii Hance to uptake heavy metals in the metalliferous soil and increased ability of plants expressing the bacterial enzyme ACC deaminase(BBa_K2384005) to accumulate heavy metals.

Overview

Hyperaccumulator was coined for plants that, differently from the excluder plants, actively take up exceedingly large amounts of one or more heavy metals from the soil. Moreover, the heavy metals are not retained in the roots but are translocated to the shoot and accumulated in aboveground organs, especially leaves and stem at concentrations 100–1000-fold higher than those found in non-hyperaccumulating species.

The major processes involved in hyperaccumulation of trace metals from the soil to the shoots by hyperaccumulators include: (a) bioactivation of metals in the rhizosphere through root–microbe interaction; (b) enhanced uptake by metal transporters in the plasma membranes; (c) detoxification of metals by distributing to the apoplasts like binding to cell walls and chelation of metals in the cytoplasm with various ligands, such as phytochelatins, metallothioneins, metal-binding proteins; (d) sequestration of metals into the vacuole by tonoplast-located transporters.

Fig. 1 Hyperaccumulator- Sedum alfredii Hance grown in the growth chamber with a 16/8 h (22/18 ℃) day/night regimes at 120 molm-2 s-1 irradiation during our phyto-experiment.(Picture by FAFU-CHINA team 2017).

Ethylene is a gaseous plant growth hormone produced endogenously by almost all plants. Apart from being a plant growth regulator, ethylene has also been established as a stress hormone. Under stress conditions like those generated by salinity, drought, waterlogging, heavy metals and pathogenicity, the endogenous production of ethylene is accelerated substantially which adversely affects the root growth and consequently the growth of the plant as a whole.

1-aminocyclopropane-1-carboxylate (ACC) deaminase(BBa_K2384005), which regulates ethylene production by metabolizing ACC (an immediate precursor of ethylene biosynthesis in higher plants) into α-ketobutyrate and ammonia，simultaneously enhances plant growth and biomass by P solubilization and uptake particularly under stress condition by heavy metals.

Fig. 2 Plants growth promoting parameters. Abbreviations: indole-3-acetic acid (IAA), methionine-S-adenosylmethionine (SAM), 1-aminocyclopropane-1-carboxylate (ACC).

Refernce

Yang, X., Feng, Y., He, Z., & Stoffella, P. J. (2005). Molecular mechanisms of heavy metal hyperaccumulation and phytoremediation, 18, 339–353. https://doi.org/10.1016/j.jtemb.2005.02.007

Ma, Y., Prasad, M. N. V, Rajkumar, M., & Freitas, H. (2011). Plant growth promoting rhizobacteria and endophytes accelerate phytoremediation of metalliferous soils Phytoremediation Bioremediation Rhizoremediation, 29, 248–258. https://doi.org/10.1016/j.biotechadv.2010.12.001

Saleem, M., Arshad, M., Hussain, S., & Saeed, A. (2007). Perspective of plant growth promoting rhizobacteria ( PGPR ) containing ACC deaminase in stress agriculture, 635–648. https://doi.org/10.1007/s10295-007-0240-6

Zhang, Y., Zhao, L., Wang, Y., Yang, B., & Chen, S. (2008). Chemosphere Enhancement of heavy metal accumulation by tissue specific co-expression of iaaM and ACC deaminase genes in plants, 72, 564–571. https://doi.org/10.1016/j.chemosphere.2008.03.043