Biochemical Plant Responses to Ozone

Abstract

Polyamine metabolism was examined in tobacco (Nicotiana tabacum L.) exposed to a single ozone treatment (5 or 7 hours) and then postcultivated in pollutant-free air. The levels of free and conjugated putrescine were rapidly increased in the ozonetolerant cultivar Bel B and remained high for 3 days. This accumulation was preceded by a transient rise of L-arginine decarboxylase (ADC, EC 4.1.1.19) activity. The ozone-sensitive cultivar Bel W3 showed a rapid production of ethylene and high levels of 1-aminocyclopropane-1-carboxylic acid after 1 to 2 hours of exposure. Induction of putrescine levels and ADC activity was weak in this cultivar and was observed when necrotic lesions developed. Leaf injury occurred in both lines when the molar ratio of putrescine to 1-aminocyclopropane-1-carboxylic acid or ethylene fell short of a certain threshold value. Monocaffeoyl-putrescine, an effective scavenger for oxyradicals, was detected in the apoplastic fluid of the leaves of cv Bel B and increased upon exposure to ozone. This extracellular localization could allow scavenging of ozone-derived oxyradicals at the first site of their generation. Induction of either polyamine or ethylene pathways may represent a control mechanism for inhibition or promotion of lesion formation and thereby contribute to the disposition of plants for ozone tolerance.Ozone (03) Fabaceae and Solanaceae, which include many crop plants, seem to be particularly sensitive (1 1, 14). Leaf damage as the most obvious pollutant effect can be observed as pigmented lesions, bleaching, chlorosis, and bifacial necrosis, depending on 03 dose and plant species. Cigar wrapper varieties of tobacco were among the first plants for which 03 damage ('weather flecks') was demonstrated (11). 03-tolerant and -sensitive lines were selected in the late 1950s. A hypersensitive line (Bel W3) from these breeding programs has been used for over 30 years as a biomonitor plant for 03 and responds to ambient concentrations with necrotic flecks that occur predominantly on the middle-aged leaves (1 1).Exposure of plants to subacute levels of 03 is now known to induce many biochemical and physiological changes (1,13,25). Several of these reactions form part of the plant's defense system toward oxidative stress, e.g. ascorbic acid and peroxidases (13), phenolic compounds (25), and polyamines (3, 13). The diamine putrescine, as well as spermidine and spermine, all commonly termed polyamines, exert several functions which counteract 03 effects. They have been implicated in an inhibition of lipid peroxidation of membranes (27), an activation of membrane-bound ATPases (13), and a reduction of ethylene formation (6,26). Polyamines were observed to accumulate in 03-treated barley (24), wheat (23), and Norway spruce (4, 25). Ethylene, which appears to be antagonistic to polyamines in senescence, is induced by 03 in many plant species (5,11,29

Constitutively Elevated Levels of Putrescine and Putrescine-Generating Enzymes Correlated with Oxidant Stress Resistance in Conyza bonariensis and Wheat

“…l), which is similar to the findings in rice, in which putrescine levels are not induced by salt stress (Krishnamurthy and Bhagwat, 1989). Conversely, putrescine biosynthesis was induced by many stresses, such as ozone (Langebartels et al, 1991;Scalet et al, 1995;Tuomainen et al, 1996), wounding (Yoza et al, 1996), osmotic stress (Flores and Galston, 1984), heat shock (Roy and Ghosh, 1996), oxygen deficiency (Reggiani et al, 1990), and K+ deficiency (Watson and Malmberg, 1996) in other species. Putrescine is known to specifically interact with proteins, nucleic acids, and membranes (Young and Galston, 1983).…”

The physiological, transcriptional and genetic responses of an ozone- sensitive and an ozone tolerant poplar and selected extremes of their F 2 progeny

“…S-adenosyl methionine (SAM) is the precursor molecule to both polyamines and ethylene (Langebartels et al, 1991;Pandey et al, 2000), both of which are thought to be involved in the response to ozone (Langebartels et al, 1991;Overmyer et al, 2005). It is of interest, therefore, that SAM Synthetase (SAMS) co-located to QTL for both late and early season visible damage on LG II.…”

Nicotinamide, a missing link in the early stress response in eukaryotic cells: A hypothesis with special reference to oxidative stress in plants

“…Many types of biotic and abiotic stress in plants cause the induction of secondary metabolism and accumulation of secondary metabolites. The plant stressors 03, UV and fungal elicitor induce secondary metabolism (stilbene production) in conifers [27,28]. This induction of secondary metabolism is associated with the induction of key enzymes of the phenylpropanoid/flavonoid pathway, 147 such as PAL and CHS.…”