Soil and foliar selenium application: Impact on accumulation, speciation, and bioaccessibility of selenium in wheat (Triticum aestivum L.)

Authors: WANG, MIN - Northwest A&f University; ZHOU, FEI - Northwest A&f University; CHENG, NAN - Northwest A&f University; CHEN, PING - Northwest A&f University; MA, YUANZHE - Northwest A&f University; ZHAI, HUI - Xinjiang University; QI, MINGXING - Northwest A&f University; LIU, NANA - Nanjing University; LUI, YANG - Northwest A&f University; MENG, LI - Ankang University; Banuelos, Gary; LIANG, DONGLI - Northwest A&f University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2022
Publication Date: 9/14/2022
Citation: Wang, M., Zhou, F., Cheng, N., Chen, P., Ma, Y., Zhai, H., Qi, M., Liu, N., Lui, Y., Meng, L., Banuelos, G.S., Liang, D. 2022. Soil and foliar selenium application: Impact on accumulation, speciation, and bioaccessibility of selenium in wheat (Triticum aestivum L.). Frontiers in Plant Science. 13. Article 988627. https://doi.org/10.3389/fpls.2022.988627.
DOI: https://doi.org/10.3389/fpls.2022.988627

Interpretive Summary: It was estimated that at least one billion people have insufficient selenium (Se) intake in the world, which may cause various diseases in humans, including hypothyroidism, infections, tumors, rheumatoid arthritis, or heart failure. Considering that organisms can’t naturally synthesize Se, human Se intake is primarily dependent on the dietary diet, mainly derived from plant food chain. Strategies to improve Se content in food crops can be achieved through biofortification practices, which involves applying Se to either the soil and/or directly onto the plant. Selenium applied to the soil can be absorbed by the plant roots or if applied to the leaves that is a foliar application, Se can enter the leave’s cuticle or stomatal pathway. Depending on the plant species, Se can then be translocated to edible parts of the plant. In this greenhouse study, wheat as world-wide consumed crop, was selected for this Se biofortification trial done in a greenhouse. We hypothesized that different Se application techniques (soil vs. foliar) with different forms of Se applied at varied rates, will affect the growth and the accumulation of Se, which may increase the availability of Se for human intake from Se-enriched wheat. Our results showed that soil applied Se increased grain yield and that both application techniques of any form of Se, especially foliar-applied selenate, will increase Se content in all parts of wheat, including wheat grains. Losses of Se occurred when a whole grain was processed into white flours. However, the bioavailability of Se for human intake was greater with the processed white flour. In conclusion, foliar applied selenite at a low rate was the most effective application method for enriching wheat grains with Se, which can be processed into Se-enriched whole wheat or white flours. Consumption of food products made from selenium-enriched wheat flour may be a useful strategy for improving Se intake for populations low in selenium.

Technical Abstract: It is estimated that over 1 billion people have insufficient selenium (Se) intake in the world, which may lead to increases in human diseases, including hypothyroidism, infections, tumors, rheumatoid arthritis, or heart failure. Comprehensive studies are needed on identifying strategies to increase Se intake so that that the dietary intake is at least 50-55 ug Se/day. Since organisms can’t synthesize Se, they are dependent on obtaining sufficient Se from plant dietary sources. Worldwide, strategies to increase Se intake are currently using Se biofortification practices that involve the application of Se to the soil or to the plant for producing Se-enriched food crops and products. Thus, in this greenhouse biofortification study, the roles of exogenous Se (selenite vs. selenate), application methods (soil vs. foliar), rates (0.5, 2, 10, and 20 mg Se /kg), and wheat growth stages for foliar application (pre-flowering and pre-filling), were investigated on Se accumulation in both wheat and subsequent processed wheat flours. Results showed that irrespective of Se species or rate, foliar and soil Se applications significantly increased the Se content in different parts of wheat. Regardless of Se application methods, the Se content of the first node was always higher than the first internode. In the wheat grains, selenomethionine (SeMet) and selenocystine (SeCys2) were the main organic Se species identified at 87%-96% and 4%-13 %, respectively, in wheat grains. The percentage of SeMet increased by 6% from plants grown in soils applied with selenite and selenate at 0.5 mg kg-1, respectively, and decreased by an average of 12% compared with soils applied with selenite and selenate at 2 mg kg-1, respectively. Processing grains from all treatments into flour, resulted in losses of Se ranging from 12%-68% in wheat and white all-purpose flours. The bioaccessibility of Se (the amount of Se bioavailable for human absorption) from both types of flour ranged from 6%-38%. In summary, foliar application of Se as 0.5 mg L-1 selenite was most efficient for producing Se-enriched wheat grains that were processed into Se-enriched whole wheat and white flours. Future studies should focus on mechanisms of Se translocation from within the wheat plant to wheat grains as influenced by speciation changes occurring within the plant after foliar application of selenate or selenite.