Diurnal Variations in Release of Phytosiderophores and in Concentrations of Phytosiderophores and Nicotianamine in Roots and Shoots of Barley

Abstract

Summary The effects of the iron (Fe) nutritional status and time of the day on the release of phytosiderophores (PS) and on concentrations of PS and their precursor nicotianamine (NA) in roots and shoots were studied over a 24-hour cycle for barley ( Hordeum vulgare L. cv. Europa). Phytosiderophores were released in a diurnal rhythm with maximum rates 5 to 6 hours after onset of the light. Compared with Fe-sufficient plants, PS release rates were up to 250 times higher in Fe-deficient plants. The dominant PS in root exudates and root and shoot extracts was epi -hydroxymugineic acid (HMA). In root extracts of Fe-deficient plants, concomitantly to release of epi -HMA, concentrations of epi -HMA decreased until the end of the highest release rate. Thereafter, epi -HMA concentrations in root extracts increased with time and were as high at the en4 of the light period as at the onset. In root extracts of Fe-sufficient plants, epi -HMA concentrations were up to 10 times lower and diurnal variations in epi -HMA concentrations were not observed. Nicotianamine concentrations were 1.5 times higher in root extracts of Fe-deficient plants than of Fe-sufficient plants and were independent of time of the day. In root extracts of Fe-deficient plants NA concentrations were up to 62 times lower than epi -HMA concentrations. In shoot extracts epi -HMA and NA concentrations were similar in Fe-sufficient and Fe-deficient plants and no consistent diurnal variations were observed. Apparently, depending on Fe nutritional status, PS are synthesized in roots at constant rates over the whole light period. No marked accumulation of NA or other precursors of epi -HMA such as deoxymugineic acid (DMA) or mugineic acid (MA) occurs under Fe deficiency.