Shen Yating, Wiita Elizabeth, Nghiem Athena A, Liu Jingyu, Haque Ezazul, Austin Rachel N, Seng Chheng Y, Phan Kongkea, Zheng Yan, Bostick Benjamin C
Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, NY 10964, USA.
National Research Center for Geo-analysis (NRCGA), Beijing 100037, China.
Plant Soil. 2023 Oct;491(1-2):605-626. doi: 10.1007/s11104-023-06140-1. Epub 2023 Jul 14.
Rice accounts for around 20% of the calories consumed by humans. Essential nutrients like zinc (Zn) are crucial for rice growth and for populations relying on rice as a staple food. No well-established study method exists. As a result, we a lack a clear picture of the chemical forms of zinc in rice grain. Furthermore, we do not understand the effects of widespread and variable zinc deficiency in soils on the Zn speciation, and to a lesser extent, its concentration, in grain.
The composition and Zn speciation of Cambodian rice grain is analyzed using synchrotron-based microprobe X-ray fluorescence (μ-XRF) and extended X-ray absorption fine-structure spectroscopy (EXAFS). We developed a method to quantify Zn species in different complexes based on the coordination numbers of Zn to oxygen and sulfur at characteristic bond lengths.
Zn levels in brown rice grain ranged between 15-30 mg kg and were not correlated to Zn availability in soils. 72%-90% of Zn in rice grains is present as Zn-phytate, generally not bioavailable, while smaller quantities of Zn are bound as labile nicotianamine complexes, Zn minerals like ZnCO or thiols.
Zn speciation in rice grain is affected by Zn deficiency more than previously recognized. A majority of Zn was bound in phytate complexes in rice grain. Zinc phytate complexes were found in higher concentrations and also in higher proportions, in Zn-deficient soils, consistent with increased phytate production under Zn deficiency. Phytates are generally not bioavailable to humans, so low soil Zn fertility may not only impact grain yields, but also decrease the fraction of grain Zn bioavailable to human consumers. The potential impact of abundant Zn-phytate in environments deficient in Zn on human bioavailability and Zn deficiency requires additional research.
大米约占人类所摄入热量的20%。锌（Zn）等必需营养素对水稻生长以及以大米为主食的人群至关重要。目前尚无成熟的研究方法。因此，我们对水稻籽粒中锌的化学形态缺乏清晰的认识。此外，我们不了解土壤中普遍存在且程度各异的锌缺乏对籽粒中锌的形态以及在较小程度上对其浓度的影响。
利用基于同步加速器的微区X射线荧光光谱法（μ-XRF）和扩展X射线吸收精细结构光谱法（EXAFS）分析柬埔寨水稻籽粒的组成和锌形态。我们开发了一种基于锌在特征键长下与氧和硫的配位数来定量不同络合物中锌形态的方法。
糙米籽粒中的锌含量在15 - 30毫克/千克之间，与土壤中锌的有效性无关。水稻籽粒中72% - 90%的锌以植酸锌的形式存在，通常无法被生物利用，而少量的锌则与不稳定的烟酰胺络合物、碳酸锌等锌矿物质或硫醇结合。
水稻籽粒中的锌形态受锌缺乏的影响比之前认为的更大。水稻籽粒中大部分锌与植酸络合。在缺锌土壤中，植酸锌络合物的浓度更高且比例也更高，这与缺锌条件下植酸产量增加一致。植酸通常无法被人体生物利用，因此土壤锌肥力低不仅可能影响谷物产量，还会降低人类消费者可利用的谷物锌比例。缺锌环境中大量的植酸锌对人体生物有效性和锌缺乏的潜在影响需要进一步研究。
