Hormonal regulation of fruitlet abscission induced by carbohydrate shortage in citrus |
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Authors: | Aurelio Gómez-Cadenas Jalel Mehouachi Francisco R Tadeo Eduardo Primo-Millo Manuel Talon |
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Institution: | (1) Departamento de Citricultura, Instituto Valenciano de Investigaciones Agrarias, Apartado Oficial, 46113 Moncada, Valencia, Spain, ES |
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Abstract: | The hormonal signals controlling fruitlet abscission induced by sugar shortage in citrus were identified in Satsuma mandarin,
Citrus unshiu (Mak.) Marc, cv. Clausellina and cv. Okitsu. Sugar supply, hormonal responses and fruitlet abscission were manipulated through
full, partial or selective leaf removals at anthesis and thereafter. In developing fruitlets, defoliations reduced soluble
sugars (up to 98%), but did not induce nitrogen and water deficiencies. Defoliation-induced abscission was preceded by rises
(up to 20-fold) in the levels of abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC) in fruitlets. Applications
to defoliated plants showed that ABA increased ACC levels (2-fold) and accelerated fruitlet abscission, whereas norflurazon
and 2-aminoethoxyvinyl glycine reduced ACC (up to 65%) and fruitlet abscission (up to 40%). Only the full defoliation treatment
reduced endogenous gibberellin A1 (4-fold), whereas exogenous gibberellins had no effect on abscission. The data indicate that fruitlet abscission induced
by carbon shortage in citrus is regulated by ABA and ACC originating in the fruits, while gibberellins are apparently implicated
in the maintenance of growth. In this system, ABA may act as a sensor of the intensity of the nutrient shortage that modulates
the levels of ACC and ethylene, the activator of abscission. This proposal identifies ABA and ACC as components of the self-regulatory
mechanism that adjusts fruit load to carbon supply, and offers a physiological basis for the photoassimilate competition-induced
abscission occurring under natural conditions.
Received: 19 February 1999 / Accepted: 14 August 1999 |
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Keywords: | : Abscission (fruit) – 1-Aminocyclopropane-1-carboxylic acid – Carbohydrate supply – Citrus (fruit abscission) – Defoliation – Phytohormone |
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