Agriculture Reference
In-Depth Information
development has passed ethylene promotes developmental processes that lead
to obvious ripening, including further ethylene production.
In the Japanese pear cv. 'Nijisseiki', which does not show a respiration
climacteric, there is little ethylene production and no evidence of an increase
in this associated with the ripening which in other respects appears normal,
whereas 'Chojura' shows a respiration and an ethylene climacteric (Downs
et al.
,
).
'Fuji' apple also fails to show a classic climacteric ethylene emission ( Jobling
and McGlasson,
). 'Hosui' is also non-climacteric (Tian
et al.
,
' apple,
and a high proportion of progeny derived from this, have innately low ethylene
production and the start of autocatalytic ethylene production can be delayed
long into storage (Knee and Tsantili,
;Fan
et al.
,
; Fellman
et al.
,
). 'Gloster
).
It has been proposed that ethylene biosynthesis is regulated by two systems.
System
; Stow
et al.
,
is initiated or controlled by an unknown factor that is probably
involved in the regulation of senescence. System
which, during the ripening of climacteric fruits, results in the production of
large amounts of ethylene in an autocatalytic process with the production of
ethylene triggering further production. Non-climacteric fruits do not have an
active System
then triggers System
.
It is thought that all ethylene production is via a common biosynthetic path-
way (Adams and Yang,
). This proceeds from methionine
to
S
-adenosyl-methionine (SAM) and from SAM to
; Tucker,
-
carboxylic acid (ACC). The conversion of SAM to ACC by the enzyme ACC
synthase is considered to be a rate-limiting step. ACC oxidase is the enzyme
required to convert ACC to ethylene; it is sensitive to oxygen concentration.
Apples also contain ACC malonyl transferase activity and malonylation may
regulate the low rate of ethylene synthesis during growth of the fruit (Knee,
-aminocyclopropane-
).
Exposure to low temperature stimulates ethylene synthesis in pears, both on
the tree and when detached. A similar response is shown by 'Golden Delicious'
apples with simultaneous increases in ACC, ethylene concentration in the gas
spaces in the fruit and total ethylene production (Knee
et al.
,
). 'Cox's
Orange Pippin' and 'Bramley's Seedling' do not show this effect. Production
of ACC oxidase, in addition to ACC synthase, is induced by chilling pre-
climacteric 'Granny Smith' apples (Lelievre
et al.
,
). A short period of cold
stimulates ethylene biosynthesis in 'Royal Gala' and 'Starking Delicious' as
well as 'Granny Smith' (Larrigaudiere
et al.
,
).
Starch and sugar content
Carbohydrate from photosynthesis is transported to developing pome fruits as
sorbitol (see Chapter
,p.
). In the fruit it is converted mainly to fructose
