Abstract
Foliar Selenium (Se) fertilizer has been widely used to accumulate Se in rice to a level that meets the adequate intake level. The Se content in brown rice (Oryza sativa L.) was increased in a dose-dependent manner by the foliar application of sodium selenite as a fertilizer at concentrations of 25, 50, 75, and 100 g Se/ha. Selenite was mainly transformed to organic Se, that is, selenomethionine in rice. Beyond the metabolic capacity of Se in rice, inorganic Se also appeared. In addition, four extractable protein fractions in brown rice were analyzed for Se concentration. The Se concentrations in the glutelin and albumin fractions saturated with increasing Se concentration in the fertilizer compared with those in the globulin and prolamin fractions. The structural analyses by fluorescence spectroscopy, Fourier transform infrared spectrometry, and differential scanning calorimetry suggest that the secondary structure and thermostability of glutelin were altered by the Se treatments. These alterations could be due to the replacements of cysteine and methionine to selenocysteine and selenomethionine, respectively. These findings indicate that foliar fertilization of Se was effective in not only transforming inorganic Se to low-molecular-weight selenometabolites such as selenoamino acids, but also incorporating Se into general rice proteins, such as albumin, globulin glutelin, and prolamin, as selenocysteine and selenomethionine in place of cysteine and methionine, respectively.
Highlights
Selenium (Se) is an essential trace element with various important biological functions in both humans and animals
Foliar spraying is more effective than soil application in terms of biotransformation from inorganic Se to organic Se, selenite foliar spraying during the heading stage can increase the Se content in agricultural crops such as rice and wheat [26,27]
It was shown that Se incorporated from soil to plant roots remained as inorganic Se in nonsupplemented rice [28]
Summary
Selenium (Se) is an essential trace element with various important biological functions in both humans and animals. Zhang et al suggested that the Se content in protein fractions decreases in the order of glutelin, prolamin, albumin, and globulin [23]. Taken together, it should be clarified how Se is metabolized and accumulated in rice, and whether the mistranslation has any effects on rice proteins. We analyzed the Se content and species in brown rice, Zhuliangyou 819 (Oryza sativa L.), with foliar fertilization of sodium selenite at several concentrations and evaluated the effects on the structure of Se-containing glutelin. We examined the structural changes of Se-containing glutelin by fluorescence spectrometry, Fourier transform infrared spectrometry (FT-IR) and differential scanning calorimetry (DSC)
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