Low bioavailability of phosphorus (P) and iron (Fe) induces morphogenetic changes in roots that lead to a higher
surface-to-volume ratio. In Arabidopsis, an enlargement in the absorptive surface area is achieved by an increase in the
length and frequency of hairs in roots of Fe- and P-deficient plants. The extra root hairs are often located in positions that
are occupied with non-hair cells under normal conditions, i.e. over a tangential wall of underlying cortical cells. An
involvement of auxin and ethylene in root epidermis cell development of Fe- and P-deficient plants was inferred from
phenotypical analysis of hormone-related Arabidopsis mutants and from the application of substances that interfere with
either synthesis, transport, or perception of the hormones. Application of the ethylene precursor 1-aminocyclopropane-1-
carboxylic acid or the auxin analog 2,4-D caused a marked increase in root hair density in plants of all growth types and
confers a phenotype characteristic of ethylene-overproducing mutants. Hormone insensitivity and application of hormone
antagonists inhibited the initiation of extranumerary root hairs induced by Fe deficiency, but did not counteract the
formation of extra hairs in response to P deprivation. A model is presented summarizing putative pathways for alterations
in root epidermal cell patterning induced by environmental stress
Low bioavailability of phosphorus (P) and iron (Fe) induces morphogenetic changes in roots that lead to a highersurface-to-volume ratio. In Arabidopsis, an enlargement in the absorptive surface area is achieved by an increase in thelength and frequency of hairs in roots of Fe- and P-deficient plants. The extra root hairs are often located in positions thatare occupied with non-hair cells under normal conditions, i.e. over a tangential wall of underlying cortical cells. Aninvolvement of auxin and ethylene in root epidermis cell development of Fe- and P-deficient plants was inferred fromphenotypical analysis of hormone-related Arabidopsis mutants and from the application of substances that interfere witheither synthesis, transport, or perception of the hormones. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid or the auxin analog 2,4-D caused a marked increase in root hair density in plants of all growth types andconfers a phenotype characteristic of ethylene-overproducing mutants. Hormone insensitivity and application of hormoneantagonists inhibited the initiation of extranumerary root hairs induced by Fe deficiency, but did not counteract theformation of extra hairs in response to P deprivation. A model is presented summarizing putative pathways for alterationsin root epidermal cell patterning induced by environmental stress
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