The Impact of Alteration of Polyunsaturated Fatty Acid Levels on C6-Aldehyde Formation of Arabidopsis thaliana Leaves

Abstract

C,-aldehydes are synthesized via lipoxygenase/hydroperoxide lyase action on polyunsaturated fatty acid (PUFA) substrates i n plant leaves. The source pools and subcellular location of the processes are unknown. A close relationship is found between the composition of PUFA and the composition of C,-aldehydes. I n the current study, this relationship was tested using the Arabidopsis PUFA mutant lines actl, fad2, fad3 fad5, fad6, and fad7. The results indicate that C,-aldehyde formation is influenced by the alteration of C, , PUFA levels. Mutants actl and fad5, which are deficient in C, , unsaturated fatty acids, had wild-type levels of C,-aldehyde production. Mutants deficient i n the chloroplast hexadecenoic acid/ oleic acid desaturase (fad6) or hexadecadienoic acid/linoleic acid desaturase (fad7) had altered C,-aldehyde formation in a pattern similar t o the changes in the PUFA. Mutations that impair phosphatidylcholine desaturase activity, such as fad2 and fad3, however, resulted in increased E-2-hexenal formation. l h e enzymes involved measurement of p H optima. The differences in C,-aldehyde formation among the fatty acid mutants of Arabidopsis appeared not t o result from alteration of lipoxygenase/hydroperoxide lyase pathway enzymes. lnvestigation of the fatty acid composition in leaf phospholipids, glycolipids, and neutral lipids and analysis of the fatty acid composition of chloroplast and extrachloroplast lipids indicate that chloroplasts and glycolipids of chloroplasts may be the source or major source of C,-aldehyde formation in Arabidopsis leaves. in C,-aldehyde production were partially characterized, includingThe C,-aldehydes, hexanal and hexenals, along with the corresponding alcohols are the major volatile compounds responsible for the "green odor" of leaves (Hatanaka et al., 1987; Gardner, 1989). Because of their low-odor threshold, C,-aldehydes may directly influence food quality. For example, Z-3-hexenal contributes to the fresh flavor of certain fruits and vegetables (Forss et al., 1962; Drawert et al., 1966;Kazeniac and Hall, 1970). Hexanal may contribute an undesirable aroma, which has limited the widespread use of soybean products (Wolf, 1975). Severa1 investigations have shown that hexanal and hexenals inhibit growth of microorganisms in vitro, particularly funga1 species, and might be involved in plant defense (Major et al., 1960;Nandi and Fries, 1976; Croft et al., 1993). Others have shown that the C,-aldehydes inhibited the germination of severa1 seed species (Nandi and Fries, 1976; Bradow and Connick, 1990; This work was supported by the U.S. Department of Agricul-* Corresponding author; e-mail dhild@ukcc.uky.edu; fax ture and the Kentucky Agricultura1 Experiment Station.

Cytochrome P450-Dependent Metabolism of Oxylipins in Tomato. Cloning and Expression of Allene Oxide Synthase and Fatty Acid Hydroperoxide Lyase

“…Previous studies indicate that chloroplast targeting peptides are present on AOS from flax and Arabidopsis (Song et al, 1993;Harms et al, 1995;Laudert et al, 1996), as well as HPL from Arabidopsis (Bate et al, 1998). A plastid location for AOS and HPL is consistent with biochemical studies demonstrating that AOS and HPL activity is associated with chloroplasts (Vick and Zimmerman, 1987;Gardner et al, 1991;Blée and Joyard, 1996;Zhuang et al, 1996). Recently, we have shown that LeAOS is imported into chloroplasts where it specifically targets to the inner membrane of the chloroplast envelope (Froehlich et al, 1999).…”

Loss of Function of FATTY ACID DESATURASE7 in Tomato Enhances Basal Aphid Resistance in a Salicylate-Dependent Manner

“…The spr2 mutation in tomato also alters the profile of C6 volatile organic compounds (VOCs) generated from linoleic acid (C18:2) and linolenic acid (C18:3) via the hydroperoxide lyase pathway (HPL), resulting in a dramatic increase in hexanal and hexanol production and a decrease in (Z)-3-hexenal and (Z)-3-hexanol (Canoles et al, 2006;Sánchez-Hernández et al, 2006). Similar shifts in volatile profiles were also observed in Atfad7 Arabidopsis plants (Zhuang et al, 1996), although overall production of C6 volatiles is reported to be extremely low in the Columbia ecotype (Duan et al, 2005;Chehab et al, 2008). HPL appears to contribute to aphid resistance in potato (Vancanneyt et al, 2001), and several VOCs have direct antibiotic effects on aphids in vitro (Hildebrand et al, 1993).…”

Formation of lipoxygenase‐pathway‐derived aldehydes in barley leaves upon methyl jasmonate treatment

“…Figure 6 shows the levels detected in triplicate tissue extracts. As described for dicotyledon leaf tissues [35–37] (3 Z )‐ plus (2 E )‐hexenal were found to be the major aldehydes in barley leaves. Upon treatment of leaf segments with JAME, a transient maximum at 24 h was detected.…”