Intracellular protons are not involved in elicitor dependent regulation of mRNAs for defence related enzymes in Chenopodium rubrum

Abstract

Protons have been implicated in the signal transduction of elicitor-generated defence reactions. To address the possible function of cytosolic acidification we determined both intracellular and extracellular pH values and phenylalanine-ammonia-lyase (PAL) and extracellular invertase (CIN1) mRNA levels of photoautotrophic suspension culture Chenopodium rubrum cells in response to a number of stimuli known to elicit defence responses. The results of these experiments show that there is no principle link between elicitor-induced persistent pH-shifts and the induction of the defence related mRNAs. Treatment with the fungal elicitor chitosan led to intracellular acidification, extracellular alkalinisation, and a rise of both PAL and CIN1 mRNA levels. However, when these pH shifts are reversed by treatment with fusicoccin, a known activator of the plasma membrane ATPase, both PAL and CIN 1 mRNA levels are also elevated. A comparison between the kinetics of intracellular acidification and the rise in PAL and CIN 1 mRNA levels in response to chitosan shows that the activation of these genes precedes intracellular acidification by 1 h, indicating that protons are not involved in the analysed signal transduction pathway leading to the induction of PAL and CIN 1 mRNAs.