Abstract
Selenium (Se) is an essential element for many organisms, but excess Se is toxic. To better understand plant Se toxicity and resistance mechanisms, we compared the physiological and molecular responses of two Arabidopsis (Arabidopsis thaliana) accessions, Columbia (Col)-0 and Wassilewskija (Ws)-2, to selenite treatment. Measurement of root length Se tolerance index demonstrated a clear difference between selenite-resistant Col-0 and selenite-sensitive Ws-2. Macroarray analysis showed more pronounced selenite-induced increases in mRNA levels of ethylene- or jasmonic acid (JA)-biosynthesis and -inducible genes in Col-0 than in Ws-2. Indeed, Col-0 exhibited higher levels of ethylene and JA. The selenite-sensitive phenotype of Ws-2 was attenuated by treatment with ethylene precursor or methyl jasmonate (MeJA). Conversely, the selenite resistance of Col-0 was reduced in mutants impaired in ethylene or JA biosynthesis or signaling. Genes encoding sulfur (S) transporters and S assimilation enzymes were up-regulated by selenite in Col-0 but not Ws-2. Accordingly, Col-0 contained higher levels of total S and Se and of nonprotein thiols than Ws-2. Glutathione redox status was reduced by selenite in Ws-2 but not in Col-0. Furthermore, the generation of reactive oxygen species by selenite was higher in Col-0 than in Ws-2. Together, these results indicate that JA and ethylene play important roles in Se resistance in Arabidopsis. Reactive oxygen species may also have a signaling role, and the resistance mechanism appears to involve enhanced S uptake and reduction.
Highlights
Selenium (Se) is an essential element for many organisms, but excess Se is toxic
These results confirm the report by Zhang et al (2006a) that an Arabidopsis Col accession was more resistant to selenite than Ws
The results presented here indicate that the higher selenite resistance of accession Col-0 compared to Ws-2 is dependent on its higher level of selenite-induced jasmonic acid (JA) and ethylene synthesis
Summary
Selenium (Se) is an essential element for many organisms, but excess Se is toxic. To better understand plant Se toxicity and resistance mechanisms, we compared the physiological and molecular responses of two Arabidopsis (Arabidopsis thaliana) accessions, Columbia (Col)-0 and Wassilewskija (Ws)-2, to selenite treatment. The generation of reactive oxygen species by selenite was higher in Col-0 than in Ws-2 Together, these results indicate that JA and ethylene play important roles in Se resistance in Arabidopsis. Due to the structural similarity between selenate (SeO422) and sulfate, plants take up selenate, the major soluble form of Se in soil, inadvertently via sulfate transporters, and metabolize it through the sulfate assimilation pathway. This leads to the reductive assimilation of selenate to the analogs of Cys and Met, SeCys and seleno-Met, respectively (Lauchli, 1993; Terry et al, 2000; Sors et al, 2005).
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