Differential Counteraction of Ethylene Effects by Gibberellin A₃ and N₆-Benzyladenine in Senescing Citrus Peel

Abstract

Treatment of mature citrus fruit (Citrus sinensis) with ethylene induced rapid chlorophyHl destruction, a rise in respiration, a release of free amino acids, aa accumulation of reducing sugars, and an appearance of phenylalanine ammonia lyase activity. Gibberellin A3 (GA3) and N6-benzyladenine (BA) opposed the effects of ethylene on chlorophyll, amino acids, and to a lesser extent, reducing sugar levels. The ethyleneinduced respiratory rise was only slightly modified by GA3 and BA. Phenylalanine ammonia lyase activity was not affected by GA3.The antagonism between ethylene and the senescence-delaying regulators GA3 and BA seems to operate mainly within the chloroplast, but might not be confined to this compartment. The accumulation of reducing sugars exhibits the antagonism although it is not apparently related to the chloroplast. Scott and Leopold (16) were the first to draw attention to the opposing effects of ethylene and GA3. Citrus rind maturation served as one of the most evident examples since it was known by then that GA3 delays the senescent color changes of citrus rind whereas ethylene accelerates them. Cytokinins also delay citrus rind coloration, in accordance with their universal senescence-delaying effects (8, 10). Opposing effects of ethylene and GA3 or BA have been reported also for the coloration of ripening tomatoes (7) and bananas (17,18). The respiratory behavior of these climacteric fruits has not, however, been altered by GA3 treatments (7,17).In the present study, we examined the ability of GA3 and BA to counteract ethylene effects associated with various cellular compartments in senescing citrus rind. MATERIALS AND METHODSDetached mature green Shamouti orange (Citrus sinensis L. Osbeck) fruits were used, unless otherwise specified. Fruits were dipped twice, for 30 sec each, in GA3, BA, or control solutions containing 5% ethanol + 0.02% Tween-20. The ethylene-releasing chemical, 2-chloroethylphosphonic acid (Ethephon), was applied to the fruit calyx as a 25-,ul droplet of 1% solution (9). GA3 and BA were applied to fruits immediately after harvest. Ethephon or ethylene gas was usually supplied 2 to 4 hr later, after the fruits had dried from the GA3 and BA solutions.Rind color changes were measured by a Hunter color differ- quantitative estimation of color development (3). According to this method, the intensity of green color is represented by negative values which rise gradually and pass to the positive range during development of yellow and orange colors. For the assay of CO2 and ethylene, samples of four fruits were placed in 2-liter glass jars at 25 C. Duplicate samples were run for each treatment. The jars were continuously ventilated (100 ml/min) with water-saturated air, with or without 12 ,ul/l ethylene. Jars were sealed for 1 hr prior to removal of jar atmosphere samples for determination of CO2 and ethylene evolution. CO2 was determined by a Packard gas chromatograph equipped with a Poropak Q column and a thermal conductivity detector. Ethylene was determined by a Packa...

Fruit splitting in ‘Nova’ hybrid mandarin in relation to the anatomy of the fruit and fruit set treatments

“…The reason why GA 3 increased set at this moment but failed to do so at full bloom was not investigated. At a later date (12 weeks after full bloom), when the fruit was 30 ram in diameter, GA 3 reduced splitting, a response which may be related to the capacity of this hormone to block the ethylene-induced senescence of citrus rind (Goldschmidt et al, 1977;GarciaLuis et al, 1986). This change in the response, which is critically time -dependent, may account for the often conflicting literature reports on the effectiveness of GA 3 sprays to reduce splitting.…”

Functions of Hormones at the Cellular Level of Organization

“…However, in view of the original meaning of synergism as "working together", one should avoid the use of the term synergism in describing opposing actions of hormones, especially since" negative synergism" as used in this context may be confused with synergistic inhibitory interaction. Examples of antagonistic interaction include the effects of ABA and auxin on root tip surface charge (T ANADA 1972) the effects of ABA and kinetin on coleoptile elongation (KHAN and DOWNING 1968), the effects of GA and tannins on enzyme biosynthesis (JACOBSON and CORCORAN 1977) and the effects of ethylene and either GA3 or cytokinin on fruit senescence (GOLDSCHMIDT et al 1977).…”

Persistence of [14C] gibberellin A3 and [3H] gibberellin A1 in senescing, ethylene treated Citrus and tomato fruit

“…Tomato fruit were held in humid, aerated 16-liter glass containers at 25°C in the dark . The ethylene releasing compound, 2-chloroethylphosphonic acid (Ethephon) was supplied as a 25 µl droplet of 1 % solution applied to the calyx [9] . Experiments consisted of 3 to 5 single fruit replicates per treatment .…”

“…GA 3 opposed some of the senescence enhancing effects of ethylene in Citrus [9,10] and tomato [5,19] and higher levels of ethylene were needed to counteract the effect of GA3 [9] .…”