PLANT PHYSIOLOGY , Vol 101, Issue 3 873-880, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Sunflower (Helianthus annuus L.) Pathogenesis-Related Proteins (Induction by Aspirin (Acetylsalicylic Acid) and Characterization)
J. L. Jung, B. Fritig and G. Hahne
Institut de Biologie Moleculaire des Plantes du Centre National de la Recherche Scientifique et Universite Louis Pasteur, 12 rue du General Zimmer, 67084 Strasbourg, France
Sunflower leaf discs floated on a solution containing aspirin
(acetylsalicylic acid) produced a set of new proteins extractable at pH 5.2
and excreted into the intercellular space. More than 80% of the proteins
found in the intercellular fluids of induced leaf discs have been
identified as pathogenesis-related (PR) proteins by their immunological
relationship with tobacco PR proteins. Members of the four major classes of
PR proteins have been characterized. Sunflower PR proteins of type 1 (PR1)
and of type 3 (PR3) were found to have acidic isoelectric points, whereas
the induced PR protein of type 2 (PR2) had a basic isoelectric point.
Members of the type 5 PR proteins (PR5), known in tobacco as thaumatin-like
proteins, showed a more complex pattern. Multiple sunflower PR5 isomers of
similar molecular weight but of different isoelectric points were excreted
from the cells in response to the aspirin treatment. PR2 and PR3 proteins
were found at very low basal levels in untreated leaves, whereas PR1 and
PR5 proteins could not be detected at all in the same extracts. Glucanase
and chitinase activities were always associated with PR2 and PR3 proteins
in partially purified sunflower extracts. All of these data indicate that,
in response to aspirin treatment, sunflower plants produce a complete set
of PR proteins characterized by an apparently exclusively extracellular
localization.
