Selenium Accumulation, Distribution, and Speciation in Spineless Prickly Pear Cactus: A Drought- and Salt-Tolerant, Selenium-Enriched Nutraceutical Fruit Crop for Biofortified Foods

Abstract

The organ-specific accumulation, spatial distribution, and chemical speciation of selenium (Se) were previously unknown for any species of cactus. We investigated Se in Opuntia ficus-indica using inductively coupled plasma mass spectrometry, microfocused x-ray fluorescence elemental and chemical mapping (mXRF), Se K-edge x-ray absorption near-edge structure (XANES) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). mXRF showed Se concentrated inside small conic, vestigial leaves (cladode tips), the cladode vasculature, and the seed embryos. Se K-edge XANES demonstrated that approximately 96% of total Se in cladode, fruit juice, fruit pulp, and seed is carbon-Se-carbon (C-Se-C). Micro and bulk XANES analysis showed that cladode tips contained both selenate and C-Se-C forms. Inductively coupled plasma mass spectrometry quantification of Se in high-performance liquid chromatography fractions followed by LC-MS structural identification showed selenocystathionine-to-selenomethionine (SeMet) ratios of 75:25, 71:29, and 32:68, respectively in cladode, fruit, and seed. Enzymatic digestions and subsequent analysis confirmed that Se was mainly present in a "free" nonproteinaceous form inside cladode and fruit, while in the seed, Se was incorporated into proteins associated with lipids. mXRF chemical mapping illuminated the specific location of Se reduction and assimilation from selenate accumulated in the cladode tips into the two LC-MS-identified C-Se-C forms before they were transported into the cladode mesophyll. We conclude that Opuntia is a secondary Se-accumulating plant whose fruit and cladode contain mostly free selenocystathionine and SeMet, while seeds contain mainly SeMet in protein. When eaten, the organic Se forms in Opuntia fruit, cladode, and seed may improve health, increase Se mineral nutrition, and help prevent multiple human cancers.

Biofortified, selenium enriched, fruit and cladode from three Opuntia Cactus pear cultivars grown on agricultural drainage sediment for use in nutraceutical foods

“…3D and 4D), and is fully supported by the XANES results. Increases and decreases in the free SeMet peak areas after protease XIV digestion, together with SDS-PAGE analysis and re-injection of the later running selenatecontaining fractions, provide additional support (in part) with our previous LCMS structural identifications (Bañuelos et al, 2011) and have contributed to a high confidence in the Se speciation reported herein for both fruit and cladode. .…”

“…255) fruit 49% and cladode 50%. Recovery percentages of total Se in digested aqueous fruit extracts were not enhanced compared to non-digested aqueous extracts after using either protease K (Bañuelos et al, 2011), or by using protease XIV. Unlike fruit, after using protease XIV recovery percentages of Se in digested aqueous extracts from cladodes were enhanced by a factor of 1.5, 1.3 and 1.9, for cladode Nos.…”

“…248 demonstrated that the Se species were 32% CSe-C and 59% selenate (Supplementary Table 2). Considering that medium-aged cladodes lack vestigial long shoot leaves, the primary site of selenate reduction and incorporation into organic Se forms found on the young cladodes, this result was not surprising (Bañuelos et al, 2011). Cladode No.…”

“…Extraction for strong anion exchange-high performance liquid chromatography-inductively coupled plasma mass spectroscopy (SAX-HPLC-ICPMS) Aqueous Se compounds were extracted according to the methods of Bañuelos et al (2011).…”

Alleviation of cadmium toxicity in cucumber (Cucumis sativus) seedlings by the application of selenium

“…For animals and humans Se is an indispensable element that is also beneficial to plants under low concentration, however Se deficiency is general in some countries, such as China, India and Egypt where it is a common problem (Bañuelos et al, 2011;Feng et al, 2013). To counteract this problem, Se content in the edible crops organs has been increased through base Se addition or foliar sprays of Se compounds (e.g.…”