posted on 2023-12-14, 08:29authored byAndrea
E. Colina Blanco, Erik Pischke, Alejandra Higa Mori, Carolin F. Kerl, Stephan Clemens, Britta Planer-Friedrich
Inorganic and methylated thioarsenates have recently
been reported
to form in paddy soil pore waters and accumulate in rice grains. Among
them, dimethylmonothioarsenate (DMMTA) is particularly relevant because
of its high cytotoxicity and potential misidentification as nonregulated
dimethylarsenate (DMA). Studying DMMTA uptake and flag leaf, grain,
and husk accumulation in rice plants during grain filling, substantial
dethiolation to DMA was observed with only 8.0 ± 0.1, 9.1 ±
0.6, and 1.4 ± 0.2% DMMTA remaining, respectively. More surprisingly,
similar shares of DMMTA were observed in control experiments with
DMA, indicating in planta DMA thiolation. Exposure
of different rice seedling varieties to not only DMA but also to arsenite
and monomethylarsenate (MMA) revealed in planta thiolation
as a common process in rice. Up to 35 ± 7% DMA thiolation was
further observed in the shoots and roots of the model plant Arabidopsis thaliana. Parameters determining the
ratio and kinetics of thiolation versus dethiolation are unknown,
yet, but less DMA thiolation in glutathione-deficient mutants compared
to wild-type plants suggested glutathione concentration as one potential
parameter. Our results demonstrate that pore water is not the only
source for thioarsenates in rice grains and that especially the currently
nonregulated DMA needs to be monitored as a potential precursor of
DMMTA formation inside rice plants.