title: α-linolenic acid concentration and not wounding per se is the key regulator of octadecanoid (oxylipin) pathway activity in rice (Oryza sativa L.) leaves.
abstract: Using an in vitro system composed of crushed leaf tissues to simulate the wounding response in rice leaves, we established that synthesis of jasmonic acid (JA) and jasmonic acid-isoleucine (JA-Ile) can only occur in unwounded tissue and, in wounded tissue, that only the chloroplast-located section of the octadecanoid pathway is active, resulting in the accumulation of 12-oxo-phytodienoic acid (OPDA). We further showed that OPDA accumulation in vitro was inhibited by 90% using the general lipase inhibitor, tetrahydrolipstatin, indicating that production of α-linolenic acid was the rate-limiting step in octadecanoid pathway activity in rice following wounding and the enzyme capacity for an active pathway was already present. We confirmed this result by showing that added α-linolenic acid stimulated OPDA synthesis in vitro and stimulated OPDA, JA and JA-Ile synthesis in vivo in unwounded tissue. Thus, the response to wounding can be mimicked by the provision of free α-linolenic acid. Our results draw attention to the key importance of lipase activity in initiation of JA and JA-Ile biosynthesis and our lack of knowledge of the cognate lipase(s), lipase substrate identity and mechanism(s) of activation in wounded and unwounded tissue.
authors.affiliation: Institute of Plant Science and Resources, Okayama University, Chuo 2-10-1, Kurashiki, Okayama 710-0046, Japan. Electronic address: john.christeller@plantandfood.co.nz.
authors.forename: John T
authors.initials: JT
authors.lastname: Christeller
authors.affiliation: Institute of Plant Science and Resources, Okayama University, Chuo 2-10-1, Kurashiki, Okayama 710-0046, Japan. Electronic address: igalis@rib.okayama-u.ac.jp.
authors.forename: Ivan
authors.initials: I
authors.lastname: Galis
mesh_terms: D012275:Oryza / Q000378:metabolism*; D054883:Oxylipins / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D017962:alpha-Linolenic Acid / Q000378:metabolism*
chemical_list: D054883:Oxylipins; D017962:alpha-Linolenic Acid
keywords: 12-oxo-phytodienoic acid; Jasmonic acid; Octadecanoid pathway; Oryza sativa; α-Linolenic acid