Cultivar variability of iron uptake mechanisms in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is the most important staple food in the world. It is rich in genetic diversity and can grow in a wide range of environments. Iron (Fe) deficiency is a major abiotic stress in crop production and in aerobic soils, where Fe forms insoluble complexes, and is not readily available for uptake. To cope with Fe deficiency, plants developed mechanisms for Fe uptake, and although rice was described as a Strategy II plant, recent evidence suggests that it is capable of utilizing mechanisms from both Strategies. The main objective of this work was to compare two cultivars, Bico Branco (japonica) and Nipponbare (tropical japonica), to understand if the regulation of Fe uptake mechanisms could be cultivar (cv.) dependent. Plants of both cultivars were grown under Fe-deficient and -sufficient conditions and physiological and molecular responses to Fe deficiency were evaluated. Bico Branco cv. developed more leaf chlorosis and was more susceptible to Fe deficiency, retaining more nutrients in roots, than Nipponbare cv., which translocated more nutrients to shoots. Nipponbare cv. presented higher levels of Fe reductase activity, which was significantly up-regulated by Fe deficiency, and had higher expression levels of the Strategy I-. OsFRO2 gene in roots, while Bico Branco cv. induced more genes involved in Strategy II.These new findings show that rice cultivars have different responses to Fe deficiency and that the induction of Strategy I or II may be rice cultivar-dependent, although the utilization of the reduction mechanisms seems to be an ubiquitous advantage.