Endogenous Ethylene and Abscisic Acid Relative to Phytogerontology

Abstract

Endogenous production of ethylene and endogenous levels of abscisic acid were measured from Hibiscus rosa-si nensis L. abscission zone explants at six stages of development: tight bud, open flower, closed flower, petal abscission, calyx abscission, and peduncle abscission.Explants acropetal and basipetal to the abscission zone produced less ethylene than the abscission zone explants. Ethylene production increased with time both prior to and during abscission, reaching a peak in the later stages of senescence after abscission was complete.Bound abscisic acid was greatest in segments acropetal to the abscission zone at the closed flower stage. Free abscisic acid was double that of bound abscisic acid in the tight bud stage with the basipetal level exceeding that of the acropetal level until flower closure. Acropetal-free abscisic acid began to rise at petal abscission increasing sharply to a peak at calyx abscission. both. However, ABA has exhibited ethylene production in pea seedlings and stimulated its production in orange peel (24). Ethylene has also been shown to enhance the effect of ABA (50). Some interactions have been observed between ethylene and other growth regulators (1,10,11,23,32,39,47,50). An investigation of endogenous levels of ABA relative to endogenous ethylene production is in order. The objective of this study was to characterize the endogenous levels of ethylene and ABA in Hibiscius rosa-sinensis L. abscission zones to determine possible cause and effect relationships during floral development. MATERIALS AND METHODSHibiscuts rosa-sinienisis L. flower stem explants were used because the abscission zone is accessible and senescence and abscission are rapid. Ethylene and ABA determinations were made from abscission zone No. 2 (Fig. 1) (Fig. 2), as defined according to the development, senescence, and abscission of the flower petals, calyx, and peduncle. Explants 1.5 cm long, with the abscission zone centered. were used for ethylene analysis (Fig. la). Explants were surface-sterilized in 0.5% sodium hypochlorite for 4 min, blotted dry, and aseptically transferred to sterile flow chambers.The flow chamber consisted of a 7 cm X 1.5 cm (i.d.) glass tube fitted at each end with a 5 cm X 4 mm (i.d.) glass tubing in a rubber stopper. The 20 explants rested on a gauze pad placed in the bottom of each chamber. The glass tubing at the top of the chamber was attached to a humidified air flow system (0.35 ml/min) similar to that described by Pratt et al. (42). Controls consisted of 1.5-cm explants acropetal to and basipetal to the abscission zone explant (Fig. la). Empty chambers were used as a check on the system. One-milliliter gas-tight plastic syringes were attached to the exhaust port of the flow chamber. The syringes remained attached without the plunger. At sampling time, a plunger was started into the syringe, the syringe was removed from the flow system, and the 1-ml sample was injected into a gas chromatograph. Gas samples were taken at 6 AM, 10 AM. and 4 PM daily for 7 days. Explant fres...

Changes of Respiration Rate, Ethylene Evolution, and Abscisic Acid Content in Developing Inflorescence and Young Fruit of Olive (Olea europaea L. cv. Konservolia)

“…The sharp increase in ethylene production (fivefold) from 4 days before FB to 7 days AFB coincides with the period of massive flower shedding. This might also be associated with pollination and petal wilting and abscission, as has been suggested by other investigators for other kinds of flowers (Blanpied 1972, Hall and Forsyth 1967, Morgan et al 1973, Reid 1985, Swanson et al 1975. The results for ethylene in this study, combined with those of Weis et al (1991), indicate that flower abscission in olive is related to ethylene production.…”

The Role of Ethylene in Corolla Unfolding in Ipomoea Nil (Convolvulaceae)

“…If previous studies are correct, it may be that the phytochrometiming event starts a cascade ofevents in which ABA may first elicit the production ofethylene which, in tum, induces corolla unfolding. ABAethylene relationships in which ABA stimulates ethylene production have been previously reported in other flowers (Swanson et al, 1975;Ronen and Mayak, 1981) but these interactions are usually associated with senescence.…”

“…ABAethylene relationships in which ABA stimulates ethylene production have been previously reported in other flowers (Swanson et al, 1975;Ronen and Mayak, 1981) but these interactions are usually associated with senescence. AVG was a gift from Maag Agrochemical Co. (Vero Beach, FL).…”

Optimal and Spatial Analysis of Hormones, Degrading Enzymes and Isozyme Profiles in Tomato Pedicel Explants During Ethylene-Induced Abscission

“…The levels of free ABA in the AZ of Hibiscus (Swanson et al 1975) and Lupinus luteus (Porter 1977) flowers were increased before separation. Our results showed that endogenous ABA in AZ of controls was reduced slightly but was promoted by ethylene-treatment.…”