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Ascorbate oxidase-dependent changes in the redox state of the apoplast modulate gene transcript accumulation leading to modified hormone signaling and orchestration of defense processes in tobacco

Lookup NU author(s): Iker Hernandez, Dr Tahar Taybi, Emeritus Professor Jerry Barnes, Professor Christine Foyer

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Abstract

The role of the redox state of the apoplast in hormone responses, signaling cascades, and gene expression was studied in transgenic tobacco (Nicotiana tabacum) plants with modified cell wall-localized ascorbate oxidase (AO). High AO activity specifically decreased the ascorbic acid (AA) content of the apoplast and altered plant growth responses triggered by hormones. Auxin stimulated shoot growth only when the apoplastic AA pool was reduced in wild-type or AO antisense lines. Oxidation of apoplastic AA in AO sense lines was associated with loss of the auxin response, higher mitogen-activated protein kinase activities, and susceptibility to a virulent strain of the pathogen Pseudomonas syringae. The total leaf glutathione pool, the ratio of reduced glutathione to glutathione disulfide, and glutathione reductase activities were similar in the leaves of all lines. However, AO sense leaves exhibited significantly lower dehydroascorbate reductase and ascorbate peroxidase activities than wild-type and antisense leaves. The abundance of mRNAs encoding antioxidant enzymes was similar in all lines. However, the day/night rhythms in the abundance of transcripts encoding the three catalase isoforms were changed in response to the AA content of the apoplast. Other transcripts influenced by AO included photorespiratory genes and a plasma membrane Ca2+ channel-associated gene. We conclude that the redox state of the apoplast modulates plant growth and defense responses by regulating signal transduction cascades and gene expression patterns. Hence, AO activity, which modulates the redox state of the apoplastic AA pool, strongly influences the responses of plant cells to external and internal stimuli. © 2006 American Society of Plant Biologists.

Publication metadata

Author(s): Pignocchi C, Kiddle G, Hernandez I, Foster SJ, Asensi A, Taybi T, Barnes J, Foyer CH

Publication type: Article

Publication status: Published

Journal: Plant Physiology

Year: 2006

Volume: 141

Issue: 2

Pages: 423-435

ISSN (print): 0032-0889

ISSN (electronic): 1532-2548

Publisher: American Society of Plant Biologists

URL: http://dx.doi.org/10.1104/pp.106.078469

DOI: 10.1104/pp.106.078469

PubMed id: 16603663

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