Control of root epidermal patterning: Effects of Fe- and P-deficiency

Abstract

Plants have evolved multifaceted mechanisms that help to enhance the bioavailability of poorly soluble P and Fe. A number of these adaptive processes are concerned with alterations in root architecture and morphology allowing for a more effective exploration of the soil. The production of extranumerary root hairs is probably the most common response to P and Fe deficiency. In some species the development of transfer cells in the rhizodermis has been observed in roots grown under limited Fe availability. In the present study we have investigated the effects of P and Fe deficiency on root hair formation and transfer cell development in various hormone-related and iron-over-accumulating mutants. It is shown that i) the formation of extra root hairs in response to Fe and P deficiency is differentially regulated, ii) the morphological alterations are controlled by the cytoplasmic nutrient level and — in contrast to the physiological responses — are not affected by shoot-derived signals, and iii) although both root hairs and transfer cells in the rhizodermis are induced by ethylene and auxin, an absolute requirement for hormones can only be inferred for the formation of root hairs induced by Fe deficiency. The role of various components of the ethylene signal transduction pathway in the formation of Fe and P deficiency-induced changes in epidermal cell fate is discussed.