The Effect of Ethylene and Propylene Pulses on Respiration, Ripening Advancement, Ethylene-Forming Enzyme, and 1-Aminocyclopropane-1-carboxylic Acid Synthase Activity in Avocado Fruit

Abstract

When early-season avocado fruit (Persea americana Mill. cv Hass) were treated with ethylene or propylene for 24 hours immediately on picking, the time to the onset of the respiratory climacteric, i.e. the lag period, remained unchanged compared with that in untreated fruit. When fruit were pulsed 24 hours after picking, on the other hand, the lag period was shortened. In both cases, however, a 24 hour ethylene or propylene pulse induced a transient increase in respiration, called the pulse-peak, unaccompanied by ethylene production (IL Eaks [1980] Am Soc Hortic Sci 105: 744-747). The pulse also caused a sharp rise in ethyleneforming enzyme activity in both cases, without any increase in the low level of 1-aminocyclopropane-1 -carboxylic acid synthase activity. Thus, the shortening of the lag period by an ethylene pulse is not due to an effect of ethylene on either of the two key enzymes in ethylene biosynthesis. A comparison of two-dimensional polyacrylamide gel electrophoresis polypeptide profiles of in vitro translation products of poly(A+) mRNA from control and ethylene-pulsed fruit showed both up-and down-regulation in response to ethylene pulsing of a number of genes expressed during the ripening syndrome. It is proposed that the pulse-peak or its underlying events reflect an intrinsic element in the ripening process that in late-season or continuously ethylene-treated fruit may be subsumed in the overall climacteric response. A computerized system that allows continuous readout of multiple samples has established that the continued presentation of exogenous ethylene or propylene to preclimacteric fruit elicits a dual respiration response comprising the merged pulse-peak and climacteric peak in series. The sequential removal of cores from a single fruit has proven an unsatisfactory sampling procedure inasmuch as coring induces wound ethylene, evokes a positive respiration response, and advances ripening.The avocado is a climacteric fruit, wherein ethylene plays a key role in ripening (7). In several varieties of avocado (e.g. cv Hass and Fuerte), fruit fail to ripen on the tree after the fruit are mature and picking initiates the ripening process

Ethylene and Wound-Induced Gene Expression in the Preclimacteric Phase of Ripening Avocado Fruit and Mesocarp Discs

“…Within 2 to 3 h, single fruit were placed in 500-mL leakproof plastic canisters (Tupperware) fitted with input and output ports and kept at 2OoC in a constant-temperature incubator. The fruit'were treated with a continuous 30 mL/ min flow of water-saturated air or propylene at 500 pL/L in air, propylene being an effective ethylene analog that permits the determination of endogenous ethylene production in response to treatment by exogenous propylene (Eaks, 1980;Starrett and Laties, 1991a). A system of control valves allowed easy switching of gas mixtures during the course of an experiment.…”

“…cv Hass) were harvested and treated as described previously (Starrett and Laties, 1991a). Fruit were harvested from the University of California South Coast Field Station between 10 and 12 AM, or from an orchard in Carpenteria, CA, between 11 AM and 1 PM.…”

“…A system of control valves allowed easy switching of gas mixtures during the course of an experiment. Respiration was measured every hour by computer-controlled monitoring of COZ production with an IRGA (Anarad, model AR500) (Starrett and Laties, 1991a).…”

“…Although there is no reason to believe that cellulase and PG influence ripening in the lag phase-since their enzyme activity is lacking in preclimacteric fruit (Awad and Young, 1979), and EFE induction has been ruled out as causative to the initiation of the climacteric (Starrett and Laties, 1991a)-nevertheless we wished to know how induction of the genes in question is influenced by pulsing and wounding and whether induction is simply triggered by ethylene or rather requires the continuous presence thereof. With respect to P-450, as will be seen, the time course and responsiveness of induction fit our criteria for lag phase involvement and resemble the behavior of severa1 genes screened from the mixed library.…”

“…Because a 24-h pulse of ethylene or propylene following harvest shortens the lag period of mid-season fruit by several days (Starrett and Laties, 1991a), whereas wounding, i.e. slicing, causes mesocarp discs to ripen swiftly, we sought to identify genes that are activated gradually through the course of the lag phase in untreated fruit, are induced sooner by pulsing, and are turned on promptly by wounding.…”