Effects of source/sink manipulation on grain zinc accumulation by winter wheat genotypes

Abstract

Agronomy practices aimed at wheat (Triticum aestivum L.) grain Zn biofortification are important to alleviate Zn deficiency in humans, especially for those resource-poor people owing to subsistence on diets dominated by cereal-based foods with low concentrations and bioavailability of Zn. To promote understanding of source-sink flow processes affecting biofortification of wheat with Zn, effects of different source/sink manipulations on grain Zn accumulation by wheat were examined in pot and field at two locations. Treatments included foliar applications of deionized water, sucrose, ZnSO4, sucrose + Zn, defoliation, spike shading or partial removal of spikes. Results showed sucrose + Zn significantly increased grain Zn concentration more than Zn alone. Grain Zn concentration with sucrose + Zn averaged 66 mg kg -1 for 'Kenong 9204' and 59 mg kg -1 for 'Liangxing 99' in pot, and ranged from 42 to 58 mg kg -1 for 'Liangxing 99', 'Jinan 17', 'Jimai 20', 'Jimai 22', and 'Luyuan 502' under field, approaching the field-grown target 60 mg kg -1 proposed by World Health Organization. Molar ratios of phytic acid/Zn and phytic acid × Ca/Zn of 'Jinan 17', 'Jimai 20' or 'Luyuan 502' with sucrose + Zn were reduced to be < 15 and < 200, respectively, suggesting higher Zn bioavailability. Defoliation or spike shading decreased grain weight, Zn concentration and content. It is concluded that grain Zn accumulation of wheat can be affected by the sourcesink relationship of Zn and/or carbohydrate, and the foliar spray 'sucrose + Zn' is recommended for increasing concentration and bioavailability of Zn in wheat grains.

Foliar Zn Spraying Simultaneously Improved Concentrations and Bioavailability of Zn and Fe in Maize Grains Irrespective of Foliar Sucrose Supply

“…In the current study, foliar Zn and/or sucrose applications did not affect the yield or other agronomic traits of maize in Quzhou and Licheng (Tables 3 and 4), suggesting that the dry-matter accumulation in maize grains is less dependent on exogenous foliar Zn and/or carbohydrate supply, at least under the conditions used in this study. Similar results were previously reported for maize and wheat under pot or field conditions [3,26,27,35,38,50,51]. For Zn, this finding may be attributed to the high Zn concentration in soil and the suitable soil conditions, and thus the good Zn nutritional status of plants.…”

“…In 1953, it was reported that the addition of sucrose to urea sprays reduced the injury of maize leaves, perhaps by reducing the rate of urea absorption and increasing the rate of urea translocation within the plant [62]. In our previous studies, foliar application of sucrose + Zn was associated with greater improvements in the concentration, content, and bioavailability of Zn in wheat (a C3 plant) than the spraying of Zn only [3,35]. As mentioned by Zhao et al (2014) [51], the relatively higher effectiveness of sucrose + Zn may be attributed to (1) the longer drying time of the spraying solution;…”

Elucidating the source–sink relationships of zinc biofortification in wheat grains: A review

“…Previous approaches for investigating the source–sink limitations of crop assimilates for grain growth and dry matter accumulation involve reducing the carbohydrate source from photosynthesis (e.g., through defoliation or spike shading) or reducing the grain sink size (e.g., through 50% spikelet removal) after anthesis (Austin & Edrich, 1975; Chang & Zhu, 2017). These approaches have also been applied to investigate the source–sink relationship of micronutrient accumulation in wheat grains (Xia, Xue, Kong, et al, 2018; Zhang, Zhang, et al, 2012; Zhang, Zhou, Zhang, & Wang, 2008). Zhang et al.…”

“…Zhang et al. (2008), Zhang, Zhang, et al (2012) and Xia, Xue, Kong, et al (2018) all reported experiments whereby defoliation, spike shading, and spikelet removal were employed to manipulate the source or sink of Zn and dry matter in wheat plants. Their results suggested that the accumulation of Zn and dry matter in grains is restricted by source supply and sink capacity, but the effects of reducing source supply or sink capacity on grain Zn concentrations are inconsistent: (a) Defoliation by removing all the leaf blades from tagged culms decreased the source‐to‐sink ratio, which led to decreases in grain Zn concentrations in the studies of Zhang et al.…”

“…However, wheat grains contain inherently low Zn, too low to meet daily human nutritional requirements, particularly when grown on Zn‐deficient soils (Cakmak & Kutman, 2018). Furthermore, phytic acid (PA) and phenolic compounds act as antinutritional compounds in wheat grains and flour, which reduces the bioavailability of Zn in the human digestive tract (Gibson, Bailey, Gibbs, & Ferguson, 2010; Xia, Xue, Kong, et al, 2018; Xia, Xue, Liu, et al, 2018; Xue, Eagling, et al, 2014; Xue, Xia, McGrath, Shewry, & Zhao, 2015; Xue, Zhang, Liu, Xia, & Zou, 2016). The milling of wheat grains into white flours usually removes the Zn‐rich parts (mainly the embryo and aleurone layer) retaining only the Zn‐poor endosperm, which contains about 5–10 mg/kg Zn depending on the extraction rate, and cannot meet dietary Zn requirement (15–30 mg/kg in flour) (Brown, Hambridge, & Ranum, 2010; Cakmak, Pfeiffer, & McClafferty, 2010).…”