An iron-deficiency tolerant genotype of sorghum effectively localizes iron to the thylakoid membranes of the bundle sheath cells

Although sorghum (Sorghum bicolor L.), a C4 grass plant, requires a higher iron (Fe) concentration in its leaves for sufficient growth compared to C3 grass plants, there are differences in Fe-deficiency tolerance among sorghum genotypes. C4 plant sorghum localizes Fe in bundle sheath (BS) cells as a major site for CO2 assimilation; however, the response of chloroplasts in BS cells to Fe deficiency remains unknown. We compared the allocation of Fe and proteins involved in the photosystems between Fe-deficiency-tolerant and Fe-deficiency-susceptible sorghum genotypes. The distribution patterns of the Fe-requiring core proteins of photosystems I and II were the same in both genotypes, whereas the tolerant genotype, line D100, allocated more Fe to the BS thylakoid membranes than the susceptible genotype, regardless of Fe nutritional status and leaf Fe content. These results suggest that the tolerant D100 sorghum line has mechanisms to supply sufficient Fe to the BS thylakoid membranes.