Morphological and histochemical investigation of the response of Olea europaea leaves to fungal attack by Spilocaea oleagina

This study investigated the response of Olea europaea (cv. Conservolea) leaves to attack by the fungal pathogen Spilocaea oleagina. Cryostat and semithin sections of healthy and S. oleagina‐infected olive leaves were analysed histochemically for polyphenol oxidase (PPO) activity and tested for progr...

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Bibliographic Details
Published in:Plant pathology 2017-10, Vol.66 (8), p.1239-1247
Main Authors: Lanza, B., Ragnelli, A. M., Priore, M., Aimola, P.
Format: Article
Language:English
Subjects:
Apoptosis
Biodegradation
Cell death
Compartments
Cuticles
Degeneration
Diphenols
DNA nucleotidylexotransferase
Enzymatic activity
Enzyme activity
Enzymes
eye of peacock
Fungi
Labeling
leaf‐spot disease
Leaves
l‐DOPA reaction
Mesophyll
Oleuropein
olive leaf
Oxidase
Parenchyma
Pathogens
Plant cells
Plant diseases
Plastids
Polyphenol oxidase
Rutin
TUNEL reaction
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Summary:This study investigated the response of Olea europaea (cv. Conservolea) leaves to attack by the fungal pathogen Spilocaea oleagina. Cryostat and semithin sections of healthy and S. oleagina‐infected olive leaves were analysed histochemically for polyphenol oxidase (PPO) activity and tested for programmed cell death (PCD) induction by means of terminal deoxynucleotidyl transferase‐mediated dUTP nick end labelling (TUNEL). At all stages of infection, the fungus remained localized between the external and internal layers of cuticle without crossing the pectocellulosic layer. No PCD phenomena could be detected in plant cells at any stage of the disease. However, extensive degeneration of palisade parenchyma cells was observed in advanced infections, with massive loss of cytoplasmic contents and disappearance of cell compartments. Polyphenol oxidases are enzymes that, in olive, oxidize o‐diphenols (principally oleuropein and rutin) to produce o‐diquinones and melanins, substances that are toxic to many pathogens. No significant increase in overall PPO activity was found in infected leaves; on the contrary, enzyme activity was gradually lost as infection progressed, most probably due to degradation of plastids within mesophyll cells, in which such enzymes are normally confined. Only a limited local PPO activation occurred in a few upper epidermal cells of the leaf, indicating a feeble induction of a plant response.
ISSN:0032-0862
1365-3059
DOI:10.1111/ppa.12671