INTRACELLULAR THIONINS OF BARLEY - A 2ND GROUP OF LEAF THIONINS CLOSELY RELATED TO BUT DISTINCT FROM CELL WALL-BOUND THIONINS

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  • 25 May 1989
    • journal article
    • research article
    • Vol. 264  (15) , 8978-8984
Abstract
Leaf thionins of barley have been identified as a novel class of cell wall proteins, toxic to plant pathogenic fungi, and possible involve din the defense mechanism of plants (Bohlmann, H., Clausen, S., Behnke, S., Giese, H., Hiller, C., Reimann-Philipp, U., Scharder, G., Barkholt, V., and Apel, K., (1988) EMBO J. 7, 1559-1565). In the present work a second subfraction of thionins has been detected within the leaf cell, mainly in the vacuole. Thionins of both groups are closely related to each other. They are toxic to phytopathogenic fungi as well as to plant protoplasts, they share similar amino acid sequences, and their synthesis in eitolated seedlings of barley is down-regulated by light. Despite these similarities each of the two subfractions of thionins could be clearly distinguished by its subcellular distribution. In ultrathin sections of embedded etiolated leaf material, cell wall thionins could be immunogold labelled specifically by an antiserum raised against a fusion protein of Escherichia coli .beta.-galactosidase and the 15,000 Mr precursor polypeptide of thionins. This antiserum did not react with intracellular thionins. Inversely, intracellula thionins were recognized specifically by an antiserum raised against soluble leaf thionins. The possible function of intracellular thionins as part of a defense mechanism has been discussed.