Induction of systemic stress tolerance by brassinosteroid in Cucumis sativus

• Published in: The New phytologist 2011-08, Vol.191 (3), p.706-720
• Main Authors: Xia, Xiao-Jian, Zhou, Yan-Hong, Ding, Ju, Shi, Kai, Asami, Tadao, Chen, Zhixiang, Yu, Jing-Quan
• Format: Article
• Language: English
• Subjects: Accumulation; Adaptation, Physiological - drug effects; Biosynthesis; brassinosteroid biosynthesis; Brassinosteroids; Brassinosteroids - pharmacology; Chlorophyll; Chlorophyll - metabolism; Chlorophylls; Confocal microscopy; Continuous production; Cucumbers; Cucumis sativus - drug effects; Cucumis sativus - genetics; Cucumis sativus - growth & development; Cucumis sativus - physiology; DNA; Fluorescence; Foliar applications; Fusarium - physiology; Gene expression; Gene Expression Regulation, Plant - drug effects; Genes; Genes, Plant - genetics; Hormones; Hydrogen peroxide; Hydrogen Peroxide - metabolism; Lasers; Leaves; Microscopy; New class; Nucleotide sequence; Oxidative stress; Pathogens; PCR; phytohormones; Plant Diseases - immunology; Plant Diseases - microbiology; Plant growth; Plant Growth Regulators - pharmacology; Plant growth substances; Plant hormones; Plant Immunity - drug effects; Plant Leaves - drug effects; Plant Leaves - genetics; Plant Leaves - growth & development; Plant Leaves - physiology; Plant roots; Plant Roots - drug effects; Plant Roots - genetics; Plant Roots - growth & development; Plant Roots - physiology; Plant stress; Plants; Pulse amplitude modulation; Reactive oxygen species; Reactive Oxygen Species - metabolism; Scanning microscopy; Signal Transduction; Spectrophotometry; Steroids, Heterocyclic - pharmacology; Stress tolerance; Symptoms; systemic signal; Wilt
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2011.03745.x

Brassinosteroids (BRs) are a new class of plant hormones that are essential for plant growth and development. Here, the involvement of BRs in plant systemic tolerance to biotic and abiotic stresses was studied. The effects of 24-epibrassinolide (EBR) on plant stress tolerance were studied through the assessment of symptoms of photooxidative stress by chlorophyll fluorescence imaging pulse amplitude modulation, the analysis of gene expression using quantitative real-time PCR and the measurement of hydrogen peroxide (H₂O₂) production using a spectrophotometric assay or confocal laser scanning microscopy. Treatment of primary leaves with EBR induced systemic tolerance to photooxidative stress in untreated upper and lower leaves. This was accompanied by the systemic accumulation of H₂O₂ and the systemic induction of genes associated with stress responses. Foliar treatment of EBR also enhanced root resistance to Fusarium wilt pathogen. Pharmacological study showed that EBR-induced systemic tolerance was dependent on local and systemic H₂O₂ accumulation. The expression of BR biosynthetic genes was repressed in EBR-treated leaves, but elevated significantly in untreated systemic leaves. Further analysis indicated that EBR-induced systemic induction of BR biosynthetic genes was mediated by systemically elevated H₂O₂. These results strongly argue that local EBR treatment can activate the continuous production of H₂O₂, and the autopropagative nature of the reactive oxygen species signal, in turn, mediates EBR-induced systemic tolerance.