Differential Metabolisms of Green Leaf Volatiles in Injured and Intact Parts of a Wounded Leaf Meet Distinct Ecophysiological Requirements

Almost all terrestrial plants produce green leaf volatiles (GLVs), consisting of six-carbon (C6) aldehydes, alcohols and their esters, after mechanical wounding. C6 aldehydes deter enemies, but C6 alcohols and esters are rather inert. In this study, we address why the ability to produce various GLVs in wounded plant tissues has been conserved in the plant kingdom. The major product in completely disrupted Arabidopsis leaf tissues was (Z)-3-hexenal, while (Z)-3-hexenol and (Z)-3-hexenyl acetate were the main products formed in the intact parts of partially wounded leaves. 13C-labeled C6 aldehydes placed on the disrupted part of a wounded leaf diffused into neighboring intact tissues and were reduced to C6 alcohols. The reduction of the aldehydes to alcohols was catalyzed by an NADPH-dependent reductase. When NADPH was supplemented to disrupted tissues, C6 aldehydes were reduced to C6 alcohols, indicating that C6 aldehydes accumulated because of insufficient NADPH. When the leaves were exposed to higher doses of C6 aldehydes, however, a substantial fraction of C6 aldehydes persisted in the leaves and damaged them, indicating potential toxicity of C6 aldehydes to the leaf cells. Thus, the production of C6 aldehydes and their differential metabolisms in wounded leaves has dual benefits. In disrupted tissues, C6 aldehydes and their α,β-unsaturated aldehyde derivatives accumulate to deter invaders. In intact cells, the aldehydes are reduced to minimize self-toxicity and allow healthy cells to survive. The metabolism of GLVs is thus efficiently designed to meet ecophysiological requirements of the microenvironments within a wounded leaf

Detoxification of Reactive Carbonyl Species by Glutathione Transferase Tau Isozymes

Oxidative stimuli to living cells results in the formation of lipid peroxides, from which various aldehydes and ketones (oxylipin carbonyls) are inevitably produced. Among the oxylipin carbonyls, those with an α,β-unsaturated bond are designated as reactive carbonyl species (RCS) because they have high electrophilicity and biological activity. Plants have arrays of dehydrogenases and reductases to metabolize a variety of RCS that occur in the cells, but these enzymes are not efficient to scavenge the most toxic RCS (i.e., acrolein) because they have only low affinity. Two glutathione transferase (GST) isozymes belonging to the plant-specific Tau class were recently observed to scavenge acrolein with KM values at a submillimolar level. This suggests that GST could also be involved in the defense system against RCS. We tested the activities of 23 Tau isozymes of Arabidopsis thaliana for five types of RCS, and the results revealed that 11 isozymes recognized either acrolein or 4-hydroxy-(E)-2-nonenal or both as a substrate(s). Such RCS-scavenging activities indicate the potential contribution of GST to RCS scavenging in plants, and they may account for the stress tolerance conferred by several Tau isozymes. RCS are therefore a strong candidate for endogenous substrates of plant GSTs

Lipid peroxidation-derived reactive carbonyl species (RCS): Their interaction with ROS and cellular redox during environmental stresses

WOS: 000474677000013It is well known that environmental stress conditions enhance the production of reactive oxygen species (ROS), which have dual roles with damaging effects to biomolecules and with signaling roles. When enzymatic or non enzymatic antioxidant defense of the cell is overwhelmed with excess production of ROS, it results in disruption of lipids via oxidation, which causes production of highly reactive lipid peroxidation-derived molecules such as 4-hydroxy-2-nonenal, 4-hydroxy-2-hexenal, malondialdehyde and acrolein. These unstable molecules are named as reactive carbonyl species (RCS) and high concentrations of RCS can cause irreversible damage in plant cells, which ultimately leads to cell death. Although there is a vast amount of studies on the nature of RCS in animals, studies in plants are limited, which mostly investigate their detoxification mechanisms and their damaging effects. Recently, just like ROS, signal roles are being postulated for RCS. In this review, the ROS and RCS production mechanisms and sites in plant cells are introduced and the RCS detoxification mechanisms including aldehyde dehydrogenases, aldo/keto reductases, 2-alkenal reductases and glutathione transferases are described. Moreover, besides their damaging effects, evidence related to signal roles of RCS are discussed. Also, the interaction between ROS and RCS metabolism is evaluated via RCS antioxidant defense interaction.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [117Z031]; Japan Society for the Promotion of Science (JSPS) KAKENHIMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of ScienceGrants-in-Aid for Scientific Research (KAKENHI) [17H03700]This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK, Grant no: 117Z031) and by the Japan Society for the Promotion of Science (JSPS) KAKENHI, grant no. 17H03700

Diffusion of ¹³C-<i>n</i>-hexanal and (<i>Z</i>)-3-hexenal into neighboring intact tissues.

a<p>Isotope enrichment of each compound was more than 95%.</p>b<p>Values are mean ± SE (n = 3).</p