Iron deficiency tolerance traits in wild (Hordeum maritimum) and cultivated barley (Hordeum vulgare).C R Biol. 2009 Jun; 332(6):523-33.CR
Phytosiderophores (PS) are Fe(III)-solubilizing compounds released by Poaceae roots under iron deficiency conditions. Several studies focused on the capacity of these plants to secrete PS as a center of their iron deficiency tolerance, and little information is available on other traits such as root/shoot biomass ratios, iron use efficiency, photosynthetic activity, and iron mobilization capacity that might also contribute to iron deficiency tolerance. In this study, we evaluated some traits other than PS release capacity that could be responsible for differences in iron deficiency tolerance in two barley species, Hordeum maritimum and Hordeum vulgare. Results showed that under iron starvation, biomass production was affected in both species, but H. maritimum kept higher root/shoot ratios due to the distribution efficiency of carbohydrates within the plant and the growth flexibility of its organs. Both species responded to iron starvation by an early release of PS, but they differed in their secretion capacity. In cultivated barley, the PS release rate was 1.5-2-fold higher than that of wild barley. This behavior was also concomitant with no modification in shoot iron concentration of the latter, which may lead to a low stimulation of its PS release as compared to the former. The amount of Fe(3+) mobilized by root exudates was determined at different pH values (between 5.6 and 8.6). Results showed a decrease in the mobilization capacity with the increasing pH, mainly in H. vulgare. At 8.6, it was reduced by 50% in H. vulgare and 30% in H. maritimum. These data suggest that differences in Poaceae tolerance to iron deficiency is attributed not only to PS secretion capacity, but also to carbohydrate distribution within the plant, Fe use efficiency, and root exudates capacity to mobilize Fe(III).