Intracellular Levels of Free Linolenic and Linoleic Acids Increase in Tomato Leaves in Response to Wounding

Abstract

An intracellular signaling pathway for activating plant defense genes against attacking herbivores and pathogens is mediated by a lipid-based signal transduction cascade. I n this pathway, linolenic acid (18:3) is proposed to be liberated from cell membranes and is converted to cyclopentanones that are involved in transcriptional regulation of defense genes, analogously to prostaglandin synthesis and function in animals. Levels of 18:3 and linoleic acid in tomato (Lycopersicon esculentum) leaves increased within 1 h when the leaves were wounded with a hemostat across the main vein t o simulate herbivore attacks. The increase correlated with the time course of accumulation of jasmonic acid, a cyciopentanone product of 18:3, that had previously been shown t o increase i n leaves in response both to wounding and to elicitors of plant defense genes. One hour after wounding, at least a 15-fold excess of 18:3 was found over that required to account for the levels of newly synthesized jasmonic acid. The free fatty acids in both control and wounded leaves accounted for less than 0.25% of the total fatty acids. However, the total lipid contents of the leaves remained relatively unchanged up to 8 h after wounding, indicating that extensive loss of lipids did not occur, although a gradual decrease in polar lipids was observed, mainly in monogalactosyl diacylglycerol of chloroplast lipids. The data support a role for lipid release as a key step in the signaling events that activate defense genes in tomato leaves in response t o wounding by attacking herbivores. In leaves of tomato (Lycopersicon esculentum) plants, severa1defense genes are activated by herbivore attacks or other mechanical wounds that crush the tissues (Ryan, 1992; Schaller and Ryan, 1996). Among the activated genes are those encoding Ser, aspartyl, and Cys proteinase i h b i t o r s and the enzyme polyphenol oxidase. These genes are activated in leaves both nearby and distant from the wound sites (Ryan, 1992; Schaller and Ryan, 1996). The signals released to local cells have been attributed to (a) oligosaccharide fragments of the plant and/or pathogen cell walls (Bishop et al., 1984;Darvill and Albersheim, 1984), (b) 18:3 (Farmer and Ryan, 1992), a major component of plant membranes, and (c)

Transient accumulation of .ALPHA.-ketol linolenic acid (KODA) in immature flower buds of some ornamental plants

“…In accordance with this, immunocytochemical analysis revealed the specific occurrence of allene oxide cyclase, which converts allene oxide to OPDA, in ovules, the transmission tissue of the style and vascular bundles of receptacles, flower stalks, stems, petioles and roots (Hause et al 2000). This observation suggests that JA and related compounds may play some role in plant development, in addition to the response to external stimuli, such as wounding (Conconi et al 1996a;PenaCortes et al 1995), pathogen attack (Penninckx et al 1996) or UV-induced stress (Conconi et al 1996b). On the other hand, the KODA level is transiently increased at the very early stage of flower budding in D. caryophyllus, E. russelianum and P. nil.…”

Jasmonate Biosynthesis, Perception and Function in Plant Development and Stress Responses

“…At present, it is unclear whether the lipid-bound OPDA/dn-OPDA in the membranes is synthesized in situ from MGDG or DGDG or alternatively, OPDA/dn-OPDA is synthesized from free 18:3/16:3 and then incorporated into glycerol (Schaller et al, 2004). The latter possibility is supported by substantial amount of free 18:3 and 18:2 that were detected in tomato leaves after wounding (Conconi et al, 1996). However, Buseman et al (2006) have shown that within the first 15 min after wounding, levels of OPDA-dnOPDA MGDG, OPDA-OPDA MGDG, and OPDA-OPDA DGDG increased 200 to 1000 folds.…”

Methyl jasmonate-induced cell death in grapevine requires both lipoxygenase activity and functional octadecanoid biosynthetic pathway

“…5) following elicitation with 50 µM MeJA. Support for the involvement of a lipolytic activity in the biosynthesis of jasmonates came from the observations of Mueller et al (1993) and Conconi et al (1996) that elicitation or wounding of plants caused rapid and transient changes in the lipid composition of plant cell membranes. Phospholipase A2 (PLA2, Conconi et al 1996) is located in the plasma membrane and can not directly attribute to JA biosynthesis which takes place at least in the first part in chloroplasts.…”