Condensed Lignins Are Synthesized in Poplar Leaves Exposed to Ozone

Abstract

Poplar (Populus tremula ϫ alba) trees (clone INRA 717-1-B4) were cultivated for 1 month in phytotronic chambers with two different levels of ozone (60 and 120 nL L Ϫ1 ). Foliar activities of shikimate dehydrogenase (EC 1.1.1.25), phenylalanine ammonia lyase (EC 4.3.1.5), and cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) were compared with control levels. In addition, we examined lignin content and structure in control and ozone-fumigated leaves. Under ozone exposure, CAD activity and CAD RNA levels were found to be rapidly and strongly increased whatever the foliar developmental stage. In contrast, shikimate dehydrogenase and phenylalanine ammonia lyase activities were increased in old and midaged leaves but not in the youngest ones. The increased activities of these enzymes involved in the late or early steps of the metabolic pathway leading to lignins were associated with a higher Klason lignin content in extract-free leaves. In addition, stress lignins synthesized in response to ozone displayed a distinct structure, relative to constitutive lignins. They were found substantially enriched in carbon-carbon interunit bonds and in p-hydroxyphenylpropane units, which is reminiscent of lignins formed at early developmental stages, in compression wood, or in response to fungal elicitor. The highest changes in lignification and in enzyme activities were obtained with the highest ozone dose (120 nL L Ϫ1 ). These results suggest that ozone-induced lignins might contribute to the poplar tolerance to ozone because of their barrier or antioxidant effect toward reactive oxygen species.Plants submitted to ozone generally respond with a stimulation of enzymes involved in the phenylpropanoid pathway. Both the activity and transcript level of Phe ammonia lyase (PAL), the first enzyme of the phenylpropanoid pathway, have been reported to rapidly increase under ozone exposure in various herbaceous plants and forest species (Tingey et al., 1976; Heller et al., 1990;Rosemann et al., 1991; EckeyKaltenbach et al., 1994;Sharma and Davis, 1994; Booker et al., 1996;Tuomainen et al., 1996;Pääkkö nen et al., 1998). In poplar (Populus maximorwizzii ϫ Populus trichocarpa), higher levels of PAL activity were found to be associated with a greater ozone tolerance (Koch et al., 1998). Other enzymes of the phenolic secondary metabolism, such as 4-coumarate CoA ligase (Eckey-Kaltenbach et al., 1994; Booker and Miller, 1998), caffeic acid O-methyl transferase (Koch et al., 1998), and cinnamyl alcohol dehydrogenase (CAD), the enzyme involved in the synthesis of the monolignols (Galliano et al., 1993a(Galliano et al., , 1993b Eckey-Kaltenbach et al., 1994; Booker and Miller, 1998;Zinser et al., 1998), have been shown to be ozone stimulated at the activity and/or transcript level (for review, see Sandermann et al., 1998).The activation of the phenylpropanoid metabolism also has been reported for other biotic or abiotic stresses (Dixon and Paiva, 1995) such as wounding, pathogen attack, UV irradiation, heavy metals, or drought. Stress-induc...

Disruption of LACCASE4 and 17 Results in Tissue-Specific Alterations to Lignification of Arabidopsis thaliana Stems

“…By contrast, the silencing of LAC4 or LAC17 had no effect on the frequency of condensed bonds in stem lignins, except for the semidwarf lac4-2 lac17 samples (thioacidolysis yield 25% lower than the control level when calculated in mmoles per gram of lignin). This result provides further support for the hypothesis that the semidwarf phenotype of lac4-2 lac17 is induced by stress, as lignins formed in response to stress are enriched in condensed bonds (Cabané et al, 2004;Betz et al, 2009).…”

Deciphering the ozone-induced changes in cellular processes: a prerequisite for ozone risk assessment at the tree and forest levels

“…O 3 increased both enzyme activities and related gene transcript levels involved in lignin biosynthesis in Pinus sylvestris (Rosemann and Heller 1991;Zinser et al 1998), Picea abies (Galliano et al 1993a;Galliano et al 1993b;Heller et al 1990), Populus spp. (Cabané et al 2004;Di Baccio et al 2008;Koch et al 1998;Wustman et al 2001), Betula pendula (Pääkkönen et al 1998a;Tuomainen et al 1996) and Fagus sylvatica (Jehnes et al 2007;Olbrich et al 2005). The responses of the phenylpropanoid metabolism can be both fast (Koch et al 1998) and substantial (Cabané et al 2004), and the induction levels were generally correlated with O 3 concentrations (Cabané et al 2004;Galliano et al 1993b;Rosemann et al 1991).…”

Modulation of Protein S-Nitrosylation by Isoprene Emission in Poplar

“…ARA, a glycosyl hydrolase, also is connected with secondary cell wall formation and cell wall reorganization (Sumiyoshi et al, 2013). Generally, poplar leaves respond to ozone stress with an up-regulation of gene expression and enzyme activities of phenylpropanoid and lignin biosynthetic proteins (Richet et al, 2012), which lead to higher contents of condensed lignin, hydroxycinnamic acids, and flavonoids (Booker and Miller, 1998;Cabané et al, 2004). We recently described the denitrosylation of PAL and COMT in wild-type gray poplar upon ozone exposure and demonstrated for PAL that in vitro PAL activity increased as a result of denitrosylation.…”

“…We recently described the denitrosylation of PAL and COMT in wild-type gray poplar upon ozone exposure and demonstrated for PAL that in vitro PAL activity increased as a result of denitrosylation. Because PAL is a key regulatory enzyme controlling the metabolic flux in the phenylpropanoid and downstream biosynthetic pathways (Booker and Miller, 1998;Cabané et al, 2004), the activities of the other enzymes of the phenolic secondary metabolism, such as COMT and CAD, also may be rapidly regulated by S-nitrosylation. In the NE genotype but not the IE genotype, the CAD protein, catalyzing the final step in the synthesis of monolignols (Di Baccio et al, 2008), was found to be S-nitrosylated after ozone exposure (Table I).…”