Minisymposium 1: Mineral nutrition

Abs # 11001: Hydrogen Peroxide Mediates Plant Root Cell Signaling in Response to Nutrient Deprivation

Presenter:	Shin, Ryoung , rshin@danforthcenter.org
Authors	Shin, Ryoung  (A)   McIntyre, Lauren M. (B)   Schachtman, Daniel P. (A)
Affiliations:	(A): Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (B): Computational Genomics and Department of Agronomy, Purdue University, West Lafayette, Indiana 47907

Potassium is an essential nutrient required in large quantities by plants, but changes in potassium concentrations in soil may limit potassium acquisition by roots. Plants adapt to changes in potassium concentrations to ensure a supply of this nutrient, but it is not known how plant root cells sense or signal the changes that occur upon the onset of potassium deficiency. To understand how roots respond to potassium deficiency at the molecular level, we conducted microarray analyses of gene expression using Arabidopsis roots that had been deprived of potassium for two, six, and 30 hours. We found that the genes involved in reactive oxygen species (ROS) metabolism were induced when the plants were deprived of potassium. Moreover, we showed that H₂O₂ levels increased after potassium deprivation in planta and ROS accumulated in a discrete region of roots, active in uptake and translocation of potassium. Suppression of an NADPH oxidase (rhd2 mutant), which is involved in ROS production, prevented the up-regulation of several genes that are normally induced by potassium deficiency; however, the induction of high affinity potassium transport activity was unchanged. Application of H₂O₂ restored the expression of genes induced by potassium deficiency in the rhd2 mutant and was also sufficient to induce high affinity potassium transport activity in roots grown under potassium sufficient conditions. Preliminary microarray experiments identified loci related to ROS metabolism. Biochemical and physiological studies verified that specific cellular and molecular responses to potassium deficiency in Arabidopsis roots are activated by ROS. Nitrogen and phosphorus as well as potassium are essential macronutrients for plants. The response to potassium, nitrogen, and phosphorus deprivation has been characterized at whole plant level, but is poorly understood at the molecular or cellular level. To investigate whether plants respond to nitrogen and phosphorus deprivation in a way similar to potassium deprivation, we quantified the amount of H₂O₂ produced after nitrogen and phosphorus deprivation and also analyzed the ROS accumulation pattern in roots after nutrient deprivation. From these experiments, we propose that ROS produced by a NADPH oxidase (RHD2) plays an important role in the signaling pathways of potassium deficiency and, to a lesser extent, nitrogen and phosphorus deficiency.