Harpin and hydrogen peroxide both initiate programmed cell death but have differential effects on defence gene expression in Arabidopsis suspension cultures

Abstract

Programmed cell death is increasingly viewed as a key component of the hypersensitive disease resistance response of plants. The generation of reactive oxygen species (ROS) such as H2O2 triggers a cell death programme in Arabidopsis suspension cultures following challenge with the bacterial elicitor harpin. Both harpin and exogenous H2O2 initiate a cell death pathway that requires gene expression, and also act as signalling molecules to induce the expression of plant defence genes encoding enzymes such as phenylalanine ammonia-lyase (PAL), glutathione S-transferase (GST) and anthranilate synthase (ASA1), an enzyme of phytoalexin biosynthesis in Arabidopsis. H2O2 induces the expression of PAL1 and GST but not that of ASA1. Harpin initiates two signalling pathways, one leading to increased ROS generation and expression of PAL1 and GST mRNA, and another leading to increased GST and ASA1 expression, independent of H2O2.

Regulation of the Arabidopsis Transcriptome by Oxidative Stress

“…This concentration and the two time points were chosen based on earlier studies (Desikan et al, 1998a(Desikan et al, , 2000. Arabidopsis cultures have a very high H 2 O 2 scavenging capacity (Desikan et al, 1998a).…”

“…H 2 O 2 also activates mitogen-activated protein kinases (MAPKs), conserved signaling kinases that modulate gene expression and transduce cellular responses to extracellular stimuli Grant et al, 2000;Kovtun et al, 2000;Samuel et al, 2000). Furthermore, several studies indicate that H 2 O 2 is a key factor mediating programmed cell death (PCD) in response to pathogens, elicitors, and hormones (Tenhaken et al, 1995;Levine et al, 1996;Desikan et al, 1998a;Mittler et al, 1999;Solomon et al, 1999;Bethke and Jones, 2001). In addition, two recent studies have shown that H 2 O 2 is synthesized in response to exogenous abscisic acid (ABA), and that H 2 O 2 mediates, at least in part, ABA responses including stomatal closure and gene expression (Guan et al, 2000;Pei et al, 2000).…”

“…H 2 O 2 generation during the oxidative burst is one of the earliest cellular responses to potential pathogens and elicitor molecules (Lamb and Dixon, 1997). H 2 O 2 induces the expression of defense-related genes such as GST, encoding glutathione S-transferase, and PAL, encoding Phe ammonia lyase (Levine et al, 1994;Desikan et al, 1998a;Grant et al, 2000). H 2 O 2 also activates mitogen-activated protein kinases (MAPKs), conserved signaling kinases that modulate gene expression and transduce cellular responses to extracellular stimuli Grant et al, 2000;Kovtun et al, 2000;Samuel et al, 2000).…”

Size, acetylation and concentration of chitooligosaccharide elicitors determine the switch from defence involving PAL activation to cell death and water peroxide production in Arabidopsis cell suspensions

“…In some plant models, H 2 O 2 induces PCD (Desikan et al 1998, Houot et al 2001, Ren et al 2002, Gechev and Hille 2005 and in others it appears not to be required (Glazener et al 1996, Dorey et al 1999, Sasabe et al 2000, Ichinose et al 2001. Moreover, in H 2 O 2 -dependent PCD, PCD is only observed when the H 2 O 2 concentration reaches a threshold value as a result of a complex sequence of events including H 2 O 2 perception, suppression of H 2 O 2 scavengers (de Pinto et al 2002), activation of a MAPK signalling cascade (Ren et al 2002) and the co-ordinated regulation of at least 150 genes shown to be involved in controlling H 2 O 2 homeostasis (Mittler et al 2004).…”

Effect of 24-epibrassinolide treatment on the metabolism of eggplant fruits in relation to development of pulp browning under chilling stress

“…Our data appeared that lower levels of pulp browning correlated fairly well with the PAL activity, which confirms the conclusion that EBR has protective effects against pulp browning in eggplant fruit s during cold storage. It has been reported that hydrogen peroxide can induce the expression of PAL (Desikan et al 1998). Lin et al (2005) suggested that inhibiting the production of hydrogen peroxide by dimethylthiourea can decrease the PAL activity in rice cells.…”