Early production and scavenging of hydrogen peroxide in the apoplast of sunflower plants exposed to ozone.
The present work set out to define the processes involved in the early O3-induced H2O2 accumulation in sunflower plants exposed to a single pulse of 150 ppb of O3 for 4 h. Hydrogen peroxide accumulation only occurred in the apoplast and this temporally coincided with the fumigation period. The inhibitor experiments suggested that both the plasma membrane-bound NAD(P)H oxidase complex and cell-wall NAD(P)H PODs contributed to H2O2 generation. To investigate the mechanisms responsible for O3-induced H2O2 accumulation further, both production and scavenging of H2O2 were investigated in the extracellular matrix after subcellular fractionation. The results indicated that H2O2 accumulation is a complex and highly regulated event requiring the time-dependent stimulation and down-regulation of differently located enzymes, some of which are involved in H2O2 generation and degradation, not only during the fumigation period but also in the subsequent recovery period in non-polluted air. Owing to the possible interplay between H2O2 and ethylene, the time-course of ethylene emission was analysed too. Ethylene was rapidly emitted following O3 exposure, but it declined to control values as early as after 4 h of exposure. The early contemporaneous detection of increased ethylene and H2O2 levels after 30 min of exposure does not allow a clear temporal relationship between these two signalling molecules to be established.
Ranieri
A
A
Department of Agricultural Chemistry and Biotechnology, University of Pisa, Via del Borghetto 80, I-56124 Pisa, Italy. aranieri@agr.unipi.it
Castagna
A
A
Pacini
J
J
Baldan
B
B
Mensuali Sodi
A
A
Soldatini
G F
GF
D002462:Cell Membrane / Q000201:enzymology; D016166:Free Radical Scavengers / Q000378:metabolism*; D005651:Fumigation; D006368:Helianthus / Q000187:drug effects / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007700:Kinetics; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D019255:NADPH Oxidases; D010126:Ozone / Q000494:pharmacology*; D018514:Plant Structures / Q000187:drug effects / Q000502:physiology; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis; D013997:Time Factors
D016166:Free Radical Scavengers; D017392:Thiobarbituric Acid Reactive Substances; D010126:Ozone; D006861:Hydrogen Peroxide; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D016660:NAD(P)H Dehydrogenase (Quinone)