Enhancing the Chelation Capacity of Rice to Maximise Iron and Zinc Concentrations Under Elevated Atmospheric Carbon Dioxide

Roughly half of the Earth's seven billion people rely on rice as their primary source of food. The milled grain of rice, often referred to as polished or white rice, serves as a rich source of energy but is low in protein and several essential micronutrients such as iron and zinc. As a result, billions of people in rice-based countries suffer the debilitating effects of protein-energy and micronutrient malnutrition with symptoms including iron-deficiency anaemia, growth retardation and blindness. By 2050, the Earth's atmospheric carbon dioxide concentration ([CO2]) is expected to reach 550μmolmol-1, representing a 70% increase from today's concentration of 392μmolmol-1. The impacts of elevated [CO2] on plant growth will likely include agronomically useful traits such as increased biomass, yield and water-use efficiency. However, increased plant productivity is likely to be accompanied by decreased protein and micronutrient mineral concentrations of cereal grain. This review focuses on the effects of carbon dioxide-enrichment on rice physiology and nutritional composition and proposes increased activity of the Strategy II iron uptake pathway as a promising method to maintain or increase iron and zinc concentrations in rice grain, and perhaps cereal grain in general, under elevated [CO2].