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AOBPreview published online on November 16, 2004
Annals of Botany, doi:10.1093/aob/mci024
© 2004 by Annals of Botany Company
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Received June 20, 2004
Revised August 13, 2004
Accepted September 10, 2004

Article

Assessment of Inequality of Root Hair Density in Arabidopsis thaliana using the Gini Coefficient: a Close Look at the Effect of Phosphorus and its Interaction with Ethylene

ZHENXIANG HE 1, ZHONG MA 2*, KATHLEEN M. BROWN 2, and JONATHAN P. LYNCH 2

1 College of Life Sciences, Nanjing University, Nanjing 210093, P.R. China
2 Department of Horticulture, Pennsylvania State University, University Park, PA 16802, USA

* To whom correspondence should be addressed.
ZHONG MA, E-mail: john{at}louisiana.edu


  Abstract

• Background and Aims Root hair density (i.e. the number of root hairs per unit root length) in Arabidopsis thaliana varies among individual plants in response to different nutrient stresses. The degree of such variation, defined as inequality, serves as a unique indicator of the uniformity of response within a plant population to nutrient availability.

• Methods Using the Gini coefficient (G) as an inequality index, the inequality of root hair density in Arabidopsis thaliana ‘Columbia’ was evaluated under conditions of nutrient stresses; in particular the effect of phosphorus and its interaction with ethylene.

• Key Results With decreasing phosphorus concentration, root hair density increased while inequality decreased logarithmically. The addition of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) under high phosphorus increased root hair density and decreased inequality by 7-fold. Inhibition of ethylene action with 1-methylcyclopropene (MCP) and silver thiosulphate (STS) under low phosphorus decreased root hair density, and increased inequality by 9-fold and 4-fold, respectively. The ethylene action inhibitors had little effect on root hair density under high phosphorus, but inequality increased 3-fold in the presence of MCP and decreased 2-fold in the presence of STS. Compared with the control, deficiencies in S, N and K increased inequality of root hair density, whereas deficiencies in P, Ca, B, Mn, Fe, Zn, Cu and Mg decreased inequality. In particular, the inequality of root hair density increased by over 2-fold under deficiencies of N or K, but decreased 14-fold under phosphorus deficiency.

• Conclusions The inequality analysis indicates a strong correlation between prevalent signals from the environment (i.e. phosphorus stress) and the response of the plant, and the role of ethylene in this response. As the environmental signals become stronger, an increasing proportion of individuals respond, resulting in a decrease in variation in responsiveness among individual plants as indicated by reduced inequality.

Keywords: Arabidopsis thaliana, root hairs, nutrient deficiencies, phosphorus, ethylene, Gini coefficient, inequality, Lorenz curve.
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