Breakdown of middle lamella pectin by ● OH during rapid abscission in A zolla

A zolla , a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that occurs in A zolla , breakdown of wall components of abscission zone cells by ● OH is involved. Experimentally generated ● OH caused the rapid separation of abscission zone cells from detached roots and the rapid shedding of roots from whole plants. Electron microscopic observations revealed that ● OH rapidly and selectively dissolved a well‐developed middle lamella between abscission zone cells and resultantly caused rapid cell separation and shedding. Treatment of abscission zones of I mpatiens leaf petiole with ● OH also accelerated the separation of abscission zone cells. However, compared with that of A zolla roots, accelerative effects in I mpatiens were weak. A large amount of ● OH was cytochemically detected in abscission zone cells both of A zolla roots and of I mpatiens leaf petioles. These results suggest that ● OH is involved in the cell separation process not only in the rapid abscission in A zolla but also in the abscission of I mpatiens . However, for rapid abscission to occur, a well‐developed middle lamella, a unique structure, which is sensitive to the attack of ● OH , might be needed.