The effect of
water stress and subsequent
rehydration on
1-aminocyclopropane-1-carboxylic acid (ACC) content,
ACC synthase activity,
ethylene production, and leaf abscission was studied in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings. Leaf abscission occurred when drought-stressed plants were allowed to rehydrate, whereas no abscission was observed in plants under
water stress conditions. In roots of water-stressed plants, a high ACC accumulation and an increase in
ACC synthase activity were observed. Neither increase in ACC content nor significant
ethylene production were detected in leaves of water-stressed plants. After
rehydration, a sharp rise in ACC content and
ethylene production was observed in leaves of water-stressed plants. Content of ACC in xylem fluid was 10-fold higher in plants rehydrated for 2 h after
water stress than in nonstressed plants. Leaf abscission induced by
rehydration after drought stress was inhibited when roots or shoots were treated before
water stress with
aminooxyacetic acid (AOA, inhibitor of
ACC synthase) or
cobalt ion (inhibitor of
ethylene-forming enzyme), respectively. However, AOA treatments to shoots did not suppress leaf abscission. The data indicate that
water stress promotes ACC synthesis in roots of Cleopatra mandarin seedlings.
Rehydration of plants results in ACC transport to the shoots, where it is oxidized to
ethylene. Subsequently, this
ethylene induces leaf abscission.