Zinc biofortification of cereals: rice differs from wheat and barley

In their review, mainly focused on bread wheat (Triticum aestivum), durum wheat (Triticum durum) and barley (Hordeum vulgare), Palmgren et al. 1 M.G. Palmgren et al., Zinc biofortification of cereals: problems and solutions, Trends Plant Sci. 13 (2008), pp. 464–473. Article | PDF (905 K) | View Record in Scopus | Cited By in Scopus (15)[1] suggested two major bottlenecks in zinc biofortification in cereals: the root–shoot barrier and the process of grain filling. They also described problems and possible solutions of zinc biofortification in cereals and concluded or suggested that: (i) Plants accumulate excess zinc in root vacuoles. To accumulate more zinc in the shoot than physiologically necessary for plants requires enhancing root to shoot transfer of zinc. (ii) Translocation of zinc from leaves contributes more to total zinc allocated to cereal grains than concurrent zinc uptake during grain filling. (iii) In cereals the xylem is discontinuous at the base of each seed; therefore, zinc must be transferred from xylem to phloem before entering the grain. This creates a significant bottleneck for zinc accumulation in the grain. However, from our own work on zinc accumulation, we surmise that the bottlenecks are different in rice (Oryza sativa). These three aspects do not seem to apply to rice; therefore, zinc biofortification in rice differs from that in wheat and barley. (i) Palmgren et al. [1] argue that zinc that is not directly needed accumulates in root vacuoles. Data on rice, however, indicate that excess zinc is also stored in the shoots, especially in the stem [2]. In fact, root and stem zinc levels are comparable over a wide range of plant zinc mass concentration (ZnMC, mg Zn kg–1 biomass)