1. Introduction
The rate of C
2
H
4
production varies with the type of plant tissue and its stage of development.
In climacteric fruits, C
2
H
4
is produced at different rates based on fruit stage of growth. Such fruit is
characterized by a low rate of C
2
H
4
production during the preclimacteric or unripe stage basal
C
2
H
4
, followed by the climacteric, a sudden in- crease in C
2
H
4
production during fruit ripening, a phenomenon referred to as autocatalytic C
2
H
4
Abeles, 1973. After the climacteric rise, C
2
H
4
production significantly declines during the post- climacteric phase Hoffman and Yang, 1980.
Nonclimacteric fruits, on the other hand, exhibit no increase in C
2
H
4
production during matura- tion and ripening Knee et al., 1977.
Autocatalytic C
2
H
4
production is a common feature of ripening in climacteric fruit, in which
increased synthesis of C
2
H
4
is triggered by exoge- nous C
2
H
4
application Burg and Burg, 1965; Abeles, 1973. Several reports however, have
demonstrated autoinhibition of C
2
H
4
production. McMurchie et al. 1972 reported that C
2
H
4
treat- ment inhibited C
2
H
4
production of banana pulp slices. Similarly, propylene treatment, which ini-
tiated ripening, suppressed C
2
H
4
production in intact green bananas. In the non-ripening stages
of sycamore fig, C
2
H
4
acts as an autoinhibitor of its own production, but this does not occur in the
ripening stages Zeroni et al., 1976. C
2
H
4
autoin- hibition was also noticed in avocado fruit Za-
uberman and Fuchs, 1973, immature tomato locule gel tissue Atta-Aly et al., 2000 and pea
segments Saltveit and Dilley, 1978.
It has been suggested that C
2
H
4
autocatalysis involves increased synthesis of ACC synthase and
the enzyme responsible for the conversion of ACC to C
2
H
4
Riov and Yang 1982; Atta-Aly et al., 2000, whereas autoinhibition involves suppres-
sion of the activity of either both enzymes Riov and Yang, 1982 or only ACC synthase Atta-Aly
et al., 2000. Ethylene, therefore, seems to play a role in regulating its own production Yang and
Hoffman, 1984. Studies involving treatment with exogenous ethylene or propylene have indicated
that fruit response to C
2
H
4
may also serve to distinguish between climacteric and nonclimac-
teric fruits McMurchie et al., 1972. The response of harvested fruit to applied C
2
H
4
depends on various factors, including tissue sensitivity and
stage of maturation, as well as whether or not the fruit is climacteric Biale and Young, 1981.
The objectives of this work, therefore, were to study C
2
H
4
feedback mechanisms autocatalysis and autoinhibition in tomato and strawberry
fruits at different developmental stages; to deter- mine the steps in C
2
H
4
biosynthesis which con- trol C
2
H
4
feedback mechanism; to examine the relation between C
2
H
4
feedback mechanism and the behaviour of both tomato and strawberry,
climacteric and nonclimacteric fruit, respectively; to determine the most suitable stage to induce
fruit ripening with exogenous C
2
H
4
application.
2. Material and methods
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