Biochemical basis of differential selenium tolerance in arugula (Eruca sativa Mill.) and lettuce (Lactuca sativa L.)

Authors: SANTIAGO, FRANKLIN - Cornell University; SILVA, MARIA - Federal University Of Lavras; CARDOSO, ARNON - Cornell University; DUAN, YONGBO - Cornell University; GUILHERME, LUIZ - Federal University Of Lavras; Liu, Jiping; Li, Li

Submitted to: Plant Physiology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2020
Publication Date: 11/6/2020
Citation: Santiago, F., Silva, M., Cardoso, A., Duan, Y., Guilherme, L., Liu, J., Li, L. 2020. Biochemical basis of differential selenium tolerance in arugula (Eruca sativa Mill.) and lettuce (Lactuca sativa L.). Plant Physiology and Biochemistry. 157:328-338. https://doi.org/10.1016/j.plaphy.2020.11.001.
DOI: https://doi.org/10.1016/j.plaphy.2020.11.001

Interpretive Summary: Selenium biofortification in food crops is an important strategy to increase selenium intake in humans. However, crops vary greatly with their ability to tolerate selenium and the basis underlying such a variation remains to be fully understood. In this study, we investigated and compared the effects of selenium and sulfur treatments on plant growth and biochemical responses between a Se accumulator (arugula) and a non-accumulator (lettuce). We discover that the greater ability to tolerate higher selenium levels in arugula than lettuce plants is due to an efficient antioxidant defense system, as demonstrated by greater ascorbate peroxidase activity and higher levels of glutathione and non-protein thiols. Moreover, we show that the selenium accumulator has higher tolerance to selenoamino acids in proteins than the non-accumulator, unlike the popular belief. These findings advance our understanding of selenium tolerant difference between Se accumulators and non-accumulators.

Technical Abstract: Selenium (Se) biofortification in crops provides a valuable strategy to enhance human Se intake. However, crops vary greatly with their capacity in tolerating and metabolizing/accumulating Se, and the basis underlying such variations remains to be fully understood. Here, we compared the effects of Se and its analog S treatments on plant growth and biochemical responses between a Se accumulator (arugula) and a non-accumulator (lettuce). Arugula exhibited an increased biomass production in comparison with untreated controls at a higher selenate concentration than lettuce (20 µM vs. 10 µM Na2SeO4), showing better tolerance to Se. Arugula accumulated 3-folds more Se and S than lettuce plants under the same treatments. However, the Se/S assimilation as assessed by ATP sulfurylase and O-acetylserine (thiol)lyase activities was comparable between arugula and lettuce plants. Approximately 4-fold higher levels of Se in proteins under the same doses of Se treatments were observed in arugula than in lettuce, indicating that Se accumulators have better tolerance to selenoamino acids in proteins. Noticeably, arugula showed 6-fold higher ascorbate peroxidase activity and produced over 5-fold more glutathione and non-protein thiols than lettuce plants, which suggest critical roles of antioxidants in Se tolerance. Taken together, our results show that the elevated Se tolerance of arugula compared to lettuce is most likely due to an efficient antioxidant defense system. This study provides further insights into our understanding of the difference in tolerating and metabolizing/accumulating Se between Se accumulators and non-accumulators.