Citrus leaf abscission. Regulatory role of exogenous auxin and ethylene on peroxidases and endogenous growth substances

Abstract The abscission of citrus leaf explants demonstrates the well-known enhancing effect of ethylene and the delaying one of auxin when treatment is started at excision time. Total peroxidase activity increases differently in tissues of the blade, abscission zone, and petiole. The highest activity at zero time is recovered in abscission zone in which also the response to the abscission regulators is the most visible. Isoperoxidase profiles are modified in opposite directions by ethylene and auxin respectively. Both regulators affect the activity of the same cathodic and anodic isoperoxidases without any qualitative changes. By the same time, auxin-like compounds increase in isolated abscission zones at 24 h from excision and decrease at 48 h. The level of one inhibitor complex undergoes an inverse variation. It is suggested that the increase in auxin during the first stage of abscission is necessary for influencing the growth of cells which is required to cause abscission.