The role of ion channels in stomatal action, phloem physiology, and nutrient uptake – molecular and biophysical analysis

Abstract

Ion uptake from the soil and distribution within the plant body requires the co-ordinate function of differentially expressed ion channels and carriers. Individual members of the K+ channel family are involved in nutrient uptake, loading into the xylem and phloem as well as the physiology of stomatal movement. After finishing the sequence of the Arabidopsis genome, information about the entire set of ion channel genes is available. To unravel the physiological role of individual ion channel genes for plant growth and development we analysed distinct loss-of-channel function mutants. In this context we studied the cell-type specific expression pattern of K+ channel genes by real-time quantitative RT-PCR and the biophysical properties using various electrophysical techniques. Guard Cell: Due to ion channel homeostasis, plants lacking the dominant K+ uptake channel, KAT1, exhibited normal stomatal function (Szyroki et al. 2001). Root hair: Pronounced phenotypes were observed with Arabidopsis root hairs, which lacked expression of distinct K+ channels (Ivashikina et al. 2001, subm.; Reintanz et al. 2001, subm.). Phloem: In order to determine the role of ion channels in phloem physiology, we identified the AKT2/3-type channels (Marten et al. 1999; Philippar et al. 1999; Bauer et al. 2000; Ache et al. accepted). Expression of AKT2/3 in Arabidopsis is controlled by CO2 and light (Deeken et al. 2000). From the photosynthate-dependency of AKT2/3 and the phenotype of the respective knockout mutant (Deeken et al. subm.) we propose that the coupling between sugar production and allocation involves this peculiar phloem K+ channel.