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Senescence represents the last stage of flower development, ultimately culminating in the death of the petals. The senescence program is regulated by coordinated changes in gene and protein expression, and the later stages of senescence share many characteristics of programmed cell death.

The circadian clock is an endogenous cellular mechanism which allows organisms to anticipate daily environmental changes resulting from the earth’s rotation on its axis (Alabadi ., 2001). A wide variety of physiological and behavior responses in plants, animals, and some prokaryotes are regulated by the clock (Harmer , 2001; Young and Kay, 2001; McClung, 2006).

Abscission is preceded by the production of an abscission zone or layer at the base of organ. Abscission zone cells are not greatly different anatomically from the surrounding cells, but typically they are smaller and less vacuolated. Anatomical studies reveal almost complete disappearance of the middle lamella and extensive swelling and disorganization of the microfibrils in the primary wall in abscission zone cells. This changes result from the combined activities of several degrading enzymes. Several of these enzymes have been shown to be regulated by ethylene (Sexton and Roberts, 1982).

Ethylene and auxin (IAA) are important regulators of abscission. IAA retards, whilst ethylene is a potent accelerator of the process. The general rule portrays that provided the flux of IAA to the abscission zone region is maintained; the cell separation is inhibited and abscission does not occur (Addicott, 1982; Brown, 1997).

The proprietary elicitor, YEA!, is an organic patented material derived from exoskeletons of crustaceans. YEA! appears to be responsible for actually reducing ethylene biosynthesis. This was tested using triple response assays on etiolated seedlings, which is conducted using seeds germinated in the dark. Normally elongated hypocotyls (stems) are severely reduced in length by low concentrations of ethylene. When the seeds were germinated on agar medium containing 0.1 mg/mL YEA!, the results were the same as controls and indicated ethylene was not produced by the seedlings.

Abscission is a widespread physiological process that allows the natural separation of organs from the parent plant. Abscission of plant organs takes place through a highly coordinated sequence of biochemical events that leads to wall breakdown in a discrete group of cells located in predictable positions in the plant known as abscission zones (AZs).

Pistillate flower abortion (PFA), induced by excessive pollen load on female flowers and leading eventually to their abscission, affects severely fruit set and potential fruit yield in ‘Serr’ walnut variety. Such variety, owing to its nut quality, is extensively planted in Chile and in other walnut-producing areas in the world (California).

Ethylene-induced degreening is the postharvest technique used to modify the external colour of the early citrus fruit, stimulating an adequate development of its yellow–orange external colour. This process accelerates senescence by increasing the respiration rate, transpiration and dryness of button ends. The most common physiological disorders induced by degreening treatment are the rind aging as well as calyx browning and abscission.

(Campanulaceae) is an ornamental shrub native to Azores that produces long stems bearing many pink waxy bells on the terminal raceme (Crook, 1951). This study explored the sensitivity to exogenous ethylene of flowers in relation to their developmental stage in conformity with an approach to select new crops for ornamental purposes (Vonk Noordegraaf, 2000).

Alstroemeria belongs to Alstroemeriaceae family, and currently is extensively utilized as cut flower. Considering that it is an ethylene-sensitive flower, low concentration of this gas may deteriorate floral sticks, diminishing its commercial value. The effect of different ethylene concentrations on flower senescence of Alstroemeria var.