Iron efficient and inefficient oats. I. Differences in phytosiderophore release

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Abstract
It has been known for some time that graminaceous species do not respond to Fe stress in the same way as dicots. Until the recent discovery of phytosiderophores in grass species, it has not been possible to characterize known differences in the ability of various cultivars of grasses to obtain Fe. The object of this study was to determine if differences in Fe‐inefficient TAM 0–312 and Fe‐efficient Coker 227 oats are due to their abilities to release a phytosiderophore when under Fe‐deficiency stress. The two cultivars were grown in modified Hoagland solution at several levels of Fe and the release of Fe3+ solubilizing compounds (phytosiderophore), chlorosis development, and the concentration of Fe were routinely assessed as indicators of Fe stress. There was a marked difference between TAM 0–312 and Coker 227 oats in the release of phytosiderophore from their roots. The amount of phytosiderophore released from Coker 227 roots increased as the nutrient Fe concentration increased from 0 to 1.2 mg/L, but declined to near zero with 4.8 mg/L Fe. Practically no phytosiderophore was produced by TAM 0–312 oats at any level of Fe. There were also more severe chlorosis and lower leaf Fe contents with TAM 0–312 than with Coker 227 oats. Although it appears that Coker 227 may be Fe‐efficient because of its ability to respond to Fe‐deficiency stress by producing phytosiderophores, there is a question as to why relatively high concentrations of Fe in nutrient solutions were required to maintain green Coker 227 plants. Also, why was the phytosiderophore not more efficient in solubilizing Fe3+ and making it available to the plant for absorption?