PLANT PHYSIOLOGY , Vol 112, Issue 1 401-408, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Leaf Abscission Induced by Ethylene in Water-Stressed Intact Seedlings of Cleopatra Mandarin Requires Previous Abscisic Acid Accumulation in Roots
A. Gomez-Cadenas, F. R. Tadeo, M. Talon and E. Primo-Millo
Department of Citriculture, Instituto Valenciano de Investigaciones Agrarias, Moncada E-46113, Valencia, Spain
The involvement of abscisic acid (ABA) in the process of leaf abscission
induced by 1-aminocyclopropane-1-carboxylic acid (ACC) transported from
roots to shoots in Cleopatra mandarin (Citrus reshni Hort. ex Tan.)
seedlings grown under water stress was studied using norflurazon (NF).
Water stress induced both ABA (24-fold) and ACC (16-fold) accumulation in
roots and arrested xylem flow. Leaf bulk ABA also increased (8-fold),
although leaf abscission did not occur. Shortly after rehydration, root ABA
and ACC returned to their prestress levels, whereas sharp and transitory
increases of ACC (17-fold) and ethylene (10-fold) in leaves and high
percentages of abscission (up to 47%) were observed. NF suppressed the ABA
and ACC accumulation induced by water stress in roots and the sharp
increases of ACC and ethylene observed after rewatering in leaves. NF also
reduced leaf abscission (7-10%). These results indicate that water stress
induces root ABA accumulation and that this is required for the process of
leaf abscission to occur. It was also shown that exogenous ABA increases
ACC levels in roots but not in leaves. Collectively, the data suggest that
ABA, the primary sensitive signal to water stress, modulates the levels of
ethylene, which is the hormonal activator of leaf abscission. This
assumption implies that root ACC levels are correlated with root ABA
amounts in a dependent way, which eventually links water status to an
adequate, protective response such as leaf abscission.
