senescence. Internal factors influencing senescence include age, levels of plant hormones and other growth substances, and developmental processes such as
reproductive growth Gan, 2004. Ethylene plays a key role in promoting senescence of climacteric fruits and flowers although it is less effective in
stimulating non-climacteric fruits and flowers to senesce. Other promotions of senescence process include sugar, jasmonic acid JA, salicylic acid SA,
brassinosteroids BRs, and abscisic acid ABA, while cytokinins CK, Polyamines PAs, Auxin, Gibberellins are considered to delay senescence
process Gan, 2004.
2.5. Ethylene Biosynthesis and its Physiological Effects
Ethylene is synthesized by most tissues in response to stress. In particular, it is synthesized in tissues undergoing senescence or ripening Davies, 2004.
Chaves and Mello-Farias 2006 provide a thorough review of the ethylene synthesis pathway that the end of the ethylene synthesis pathway involves three
enzymes to convert methionine into ethylene Figure 1. Two of these enzymes are involved in the formation and oxidation of the immediate precursor of
ethylene, 1-aminocyclopropane-1-carboxylic acid ACC. ACC-synthase converts S-Adenosylmethionine SAM into ACC and is the rate-limiting step in the
pathway. ACC-oxidase catalyzes the conversion of ACC to ethylene. The final conversion of ACC to ethylene is oxygen dependent Kende, 1993.
Ethylene is a plant hormone influencing plant processes such as the so called triple response, maintenance of the apical hook in seedlings, stimulation of
defense responses in response to injury or diseases, release from dormancy, shoot and root growth and differentiation, adventitious root formation, leaf and fruit
abscission, flower induction in some plants, induction of femaleness of dioecious flower, flower opening, flower and leaf senescence, fruit ripeing Davies, 2004.
Of particular economic importance is the role of ethylene as an inducer of fruit ripening Bleecker and Kende, 2000. Through this action, it induces changes
in certain plant organs, such as textural changes, color changes, and tissue degradation. Some of these changes may be desirable qualities associated with
ripening; in other cases, it can bring damage or premature decay Silva, 2008. In 9
climacteric fruits, ethylene is generally thought to be regulate fruit ripening by coordinating the expression of gene responsible for 1 enhancing a rise in the rate
of respiration, 2 autocatalytic ethylene production, 3 chlorophyll degradation, 4 pigment synthesis carotenoids and flavonoids, 5 conversion of starch to sugars,
production of aroma volatiles, and 7 increase of activities of cell wall-degrading enzymes pulp and peel softening, 8 changes in pH Grey et al., 1992; Lelievre
et al., 1997; Seymour et al., 1993. Kader 2002 recommended that respiration of mangosteen fruit kept at
20
o
C should be 6-10ml CO
2
kghr. Palapol et al. 2009 measured ethylene production of mangosteen fruit stored at temperature 25
o
C and found that ethylene production at stage 1 increased linearly until stage 5 dark purple by 5 days, then
decreased slightly after stage 5.
Figure 1. The ethylene synthesis pathway modified from Chaves and Mello- Farias, 2006.
2.6. Ethylene Action and Methods for Inhibiting Ethylene Responses
