Abstract
In a previous study, we reported that the common reed accumulates water-soluble Cd complexed with an α-glucan-like molecule, and that the synthesis of this molecule is induced in the stem of the common reed under Cd stress. We studied the metabolic background to ensure α-glucan accumulation under the Cd stress conditions that generally inhibit photosynthesis. We found that the common reed maintained an adequate CO2 assimilation rate, tended to allocate more assimilated 11C to the stem, and accumulated starch granules in its stem under Cd stress conditions. AGPase activity, which is the rate-limiting enzyme for starch synthesis, increased in the stem of common reed grown in the presence of Cd. Starch accumulation in the stem of common reed was not obvious under other excess metal conditions. Common reed may preferentially allocate assimilated carbon as the carbon source for the formation of Cd and α-glucan complexes in its stem followed by prevention of Cd transfer to leaves acting as the photosynthetic organ. These responses may allow the common reed to grow even under severe Cd stress conditions.
Highlights
Common reed (Phragmites australis [(Cav.) Trin. ex Steudel]) is resistant to various abiotic stresses and has a large biomass (Mal and Narine, 2004)
We demonstrate carbon assimilation and retranslocation; the increase of AGPase activity, which is the ratelimiting enzyme for starch synthesis; and the accumulation of starch granules in the stem of common reed grown with Cd
We showed that common reed under Cd stress tends to allocate newly assimilated carbon to the stem when compared to that in control plants (Figure 2)
Summary
Common reed (Phragmites australis [(Cav.) Trin. ex Steudel]) is resistant to various abiotic stresses and has a large biomass (Mal and Narine, 2004). Responses of common reed to NaCl-salinity (Matoh et al, 1988; Kanai et al, 2007; Liu et al, 2012), drought (Pagter et al, 2005; Liu et al, 2012), and heavy metals (Wang and Peverly, 1996; Ye et al, 1997; Bonanno, 2011) have been investigated. Common reed is not a heavy-metal hyper-accumulator, and the Cd content in its shoot is often less than that in other wetland plants (Stoltz and Greger, 2002; Ali et al, 2004). Common reed has been proposed as a candidate plant for rhizofiltration, because of its large biomass and ability to accumulate Cd in its roots, decreasing the Cd concentration in water (Ali et al, 2004). The activities of antioxidant enzymes and amount of glutathione were found to be increased by Cd (Fediuc and Erdei, 2002; Pietrini et al, 2003), similar to that found in other plants (Gill and Tuteja, 2011)
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