HO OH HO OH
Figure 6-2. Formation of antifungal butyrolactones from tuliposides via an internal esterification reaction.
Some fUngi are able to metabolize the lactone form to a butyric acid form that is not inhibitory to a variety of organisms, including the tulip pathogen Fusarium oxysporum. Two important diseases of tulip are bulb rot and grey mold. Botrytis tulipae infects all parts of the tulip, including the pistils, macerating the tissue. In contrast, Botrytis cinerea does not develop on tulips in the field, but eventually infects various parts of the plant when kept in a high humidity chamber. B. cinerea never infects the flower pistils because they contain exceptionally high concentrations of tuliposides. Tuliposides are stored in cell vacuoles. Importantly, growth of the pathogen is at first intercellular. Under these conditions the pathogen does not encounter the tuliposides. It is only when the tuliposides are released from the vacuoles that the effects of their toxicity can be expressed. B. cinerea converts tuliposides into inhibitory lactones. B. tulipae converts tuliposides into hydroxycarboxylic acids which are non-toxic (Schonbeck and Schroeder, 1972).
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