Iron deficiency stress responses of five gram‐inaceous monocots

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Abstract
Plant growth, leaf chlorosis, root reductive capacity, rhizosphere pH, and phytosiderophore release capacity were used as indices to evaluate the responses of maize (Zea mays L. cv ‘clipper'), millet (Pennisetum glaucum L. cv. ‘Dwarf Gero'), sorghum (Sorghum bicolor L. cv. YG 5760), barnyard grass (Echinochloa crus galli L. cv: unknown), wheat (Triticum aestivum L. cv. ‘tonic'), and white lupin (Lupinus albus L. cv ‘lucky') to iron‐deficiency stress. Generally, root and shoot dry matter increased with iron treatment and leaves became less chlorotic. Neither the order nor the magnitude of the root reductive capacities of the monocots studied was affected by iron deprivation, but these reductive capacities and the changes in rhizosphere pH differed markedly. Significant iron stress‐induced phytosiderophore release was observed only in wheat and sorghum in which accompanying increases in rhizosphere pH were also evident. Such phytosiderophore release matched the severity of leaf chlorosis and iron uptake and depended on the form in which the element was supplied. These results, from experiments conducted in non‐axenic hydroponic cultures, indicate that in iron‐ deficiency stress mechanisms ‐ similar to those found in dicots ‐could account for iron uptake in some graminaceous monocots, and that strategy II‐type response proposed for all in this category of plants would be an over simplification.