A novel role for methyl cysteinate, a cysteine derivative, in cesium accumulation in Arabidopsis thaliana

Abstract

Phytoaccumulation is a technique to extract metals from soil utilising ability of plants. Cesium is a valuable metal while radioactive isotopes of cesium can be hazardous. In order to establish a more efficient phytoaccumulation system, small molecules which promote plants to accumulate cesium were investigated. Through chemical library screening, 14 chemicals were isolated as ‘cesium accumulators’ in Arabidopsis thaliana. Of those, methyl cysteinate, a derivative of cysteine, was found to function within the plant to accumulate externally supplemented cesium. Moreover, metabolite profiling demonstrated that cesium treatment increased cysteine levels in Arabidopsis. The cesium accumulation effect was not observed for other cysteine derivatives or amino acids on the cysteine metabolic pathway tested. Our results suggest that methyl cysteinate, potentially metabolised from cysteine, binds with cesium on the surface of the roots or inside plant cells and improve phytoaccumulation.

Glutathione and Its Biosynthetic Intermediates Alleviate Cesium Stress in Arabidopsis

“…Next, internal levels of Cys, GSH and PCs were determined in the seedlings treated with cesium and sulphur supply. In consistency with GSH2 expression ( Figure 4B) and our previous results (Adams et al, 2017), cesium treatment increased both Cys and GSH but sulphur supply did not ( Figures 5A, B). PC2 and PC3 levels were below detection limits in all the conditions tested.…”

“…The genes denoted in italics are the ones whose expression was investigated in this study. The transcripts and the metabolites indicated in red and blue were shown in this study or the previous study (Adams et al, 2017) to be increased or decreased, respectively, in response to cesium. The metabolites in green boxes are the ones with an ability to alleviate cesium-induced aerial chlorosis.…”

“…Our previous metabolic profiling has revealed a marked increase of Cys in both roots and shoots, as well as Glu and Gly to a lesser extent in shoots, in cesiumtreated plants (Adams et al, 2017). Cys and its derivative, methyl cysteinate, were also demonstrated to be capable of chelating with cesium and functioning as cesium accumulators in plants (Adams et al, 2017). A dramatic increase of Cys in response to cesium was confirmed in the current study but interestingly, BSO treatment did not further increase Cys (Figure 5), suggesting that accumulated Cys was quickly turned into other metabolites which might also have an alleviation effect.…”

“…These findings strongly suggest that not only GSH but also GSH precursors, when concomitantly treated, have their own alleviatory function or feed into the pathways other than GSH synthesis which produce alleviatory effects against cesium stress. Our previous metabolic profiling has revealed a marked increase of Cys in both roots and shoots, as well as Glu and Gly to a lesser extent in shoots, in cesiumtreated plants (Adams et al, 2017). Cys and its derivative, methyl cysteinate, were also demonstrated to be capable of chelating with cesium and functioning as cesium accumulators in plants (Adams et al, 2017).…”

“…For phytoremediation of cesium, a wide variety of plant species have been investigated in the search for a "hyperaccumulator" and biological or chemical factors which improve uptake ability of plants have been tested (Burger and Lichtscheidl, 2018). Our previous screening effort isolated a chemical compound, methyl cysteinate, which promotes cesium accumulation in plants (Adams et al, 2017). However, plants accumulating high levels of cesium suffer stunted growth.…”