Limits to the Biofortification of Leafy Brassicas with Zinc

Abstract

Many humans lack sufficient zinc (Zn) in their diet for their wellbeing and increasing Zn concentrations in edible produce (biofortification) can mitigate this. Recent efforts have focused on biofortifying staple crops. However, greater Zn concentrations can be achieved in leafy vegetables than in fruits, seeds, or tubers. Brassicas, such as cabbage and broccoli, are widely consumed and might provide an additional means to increase dietary Zn intake. Zinc concentrations in brassicas are limited primarily by Zn phytotoxicity. To assess the limits of Zn biofortification of brassicas, the Zn concentration in a peat:sand (v/v 75:25) medium was manipulated to examine the relationship between shoot Zn concentration and shoot dry weight (DW) and thereby determine the critical shoot Zn concentrations, defined as the shoot Zn concentration at which yield is reduced below 90%. The critical shoot Zn concentration was regarded as the commercial limit to Zn biofortification. Experiments were undertaken over six successive years. A linear relationship between Zn fertiliser application and shoot Zn concentration was observed at low application rates. Critical shoot Zn concentrations ranged from 0.074 to 1.201 mg Zn g −1 DW among cabbage genotypes studied in 2014, and between 0.117 and 1.666 mg Zn g −1 DW among broccoli genotypes studied in 2015-2017. It is concluded that if 5% of the dietary Zn intake of a population is currently delivered through brassicas, then the biofortification of brassicas from 0.057 to > 0.100 mg Zn g −1 DW through the application of Zn fertilisers could increase dietary Zn intake substantially.

Soil Type and Zinc Doses in Agronomic Biofortification of Lettuce Genotypes

“…It is considered the most economical solution for micronutrient deficiency in humans and animals [14]. Several studies have shown that Zn fertilization is efficient at increasing the Zn concentration in foods [13,15,16]. Yet, leafy vegetables are more suitable for achieving higher Zn concentrations than fruits, tubers, or seeds, since Zn is mainly transported through the xylem of plants [8,17].…”

Plant Nutrient Dynamics in Stressful Environments: Needs Interfere with Burdens

“…Low zinc contents in plant products are a serious issue for human nutrition, and may cause zinc deficiency for a large percentage of the worldwide population [16,23]. Biofortification was, in the past, mainly investigated in staple crops (e.g., wheat, potato).…”

“…Such transport processes and their regulation allow an accumulation of nutrients in harvested vegetative [16] or reproductive plant parts [17,18]. The mobility of an element or of certain forms of an element in the phloem is crucial for redistribution processes within the plant [13,19,20].…”

“…Biofortification was, in the past, mainly investigated in staple crops (e.g., wheat, potato). The research article by White et al [16] is focused on the zinc biofortification in leafy brassicas such as broccoli or cabbage. These plants, grown worldwide, are directly consumed by humans, and improved zinc contents in their leaves may help to provide sufficient zinc for the population in regions with inadequate zinc supplies.…”

“…Therefore, there are limits for increasing zinc levels in collected plant parts without negatively influencing the plant itself. Based on these facts, zinc biofortification of leafy brassicas must be optimized, taking into account the zinc demands for human nutrition, as well as the possible toxic effects of elevated zinc on plant growth and/or metabolism [11,16,22].…”