Auxin and ethylene promote root hair elongation in Arabidopsis

Genetic and physiological studies implicate the phytohormones auxin and eth ylene in root hair development. To learn more about the role of these compo unds, we have examined the root hair phenotype of a number of auxin- and et hylene-related mutants. In a previous study, Masucci and Schiefelbein (1996 ) showed that neither the auxin response mutations aux1 and axr1 nor the et hylene response mutations etr1 and ein2 have a significant effect on root h air initiation. In this study, we found that mutants deficient in either au xin or ethylene response have a pronounced effect on root hair length. Trea tment of wildtype, axr1 and etr1 seedlings with the synthetic auxin, 2,4-D, or the ethylene precursor ACC, led to the development of longer root hairs than untreated seedlings. Furthermore, axr1 seedlings grown in the presenc e of ACC produce ectopic root hairs and an unusual pattern of long root hai rs followed by regions that completely lack root hairs. These studies indic ate that both auxin and ethylene are required for normal root hair elongati on.