Improving zinc efficiency of cereals under zinc deficiency

One of the widest ranging abiotic stresses in world agriculture arises from low zinc (Zn) availability in calcareous soils, particularly in cereals. Cereal species greatly differ in their zinc effici ency (ZE), defined in this article as the ability of a plant to grow and yield well under Zn deficiency. ZE has been attributed mainly to the effi ciency of acquisition of Zn under conditions of low soil Zn availability rather than to its utilization or (re)-translocation within a plant. A higher Zn acquisition efficiency, further, may be due to either or all of the following: an efficient ionic Zn uptake system, better root architecture, i.e. long and fine roots with architecture favouring exploitation of Zn from larger soil volume, higher synthesis and release of Zn-mobilizing phytosiderophore by the roots and uptake of Zn-phytosiderophore complex. Seed Zn content has also been suggested to affect ZE. This article attempts to examine critically the scanty and scattered reports available on the status of Zn defi ciency globally; morphological, biochemical and physiological basis of regulation of ZE in cereals and approaches to improve ZE in terms of grain productivity and grain Zn vis-à-vis its bioavailability under conditions of poor Zn availability. A causal relationship between important Zn-containing enzymes, viz. carbonic anhydrase (CA), Cu/Zn-superoxide dismutase (SOD) activities and ZE is reported in wheat and other cereal species. Enhanced production and release of Fe-mobilizing phytometallophores known as phytosiderophores (PS), is another mech anism relevant for cereal species in adaptation to zinc deficiency.