Agriculture Reference
In-Depth Information
Physiology
Pineapple, like most other succulents, fixes 40% to 100%
of its carbon in the dark via phosphoenolpyruvate
carboxylase, storing the carbon as malic acid. The CO 2 is
released from the malic acid in the light and is then fixed
via conventional C3 photosynthesis, a process referred to
as Crassulacean acid metabolism (CAM). Pineapple is
one of the typical PCK-CAM plants (Hong et al . 2004)
which have significant activities of PCK (pyruvate
carboxykinase) with lower levels of malic enzyme (ME)
(Winter & Smith 1996). Malate decarboxylation is a very
important metabolism in plant mitochondria, especially
in CAM plants in which malate is accumulated in the
vacuoles at night and released into the cytoplasm during
the day. Based on malate metabolism, CAM plants are
divided into ME-CAM and PCK-CAM. ME-CAM plants
have significant activities of malic enzyme without PCK,
and they use ME to decarboxylate malate, generating
pyruvate and CO 2 (Cuevas & Podestá 2000).
Pineapple is a nonclimacteric fruit but does produce
ethylene gas. When ethylene gas levels ranging from 0.01
to 1000 μl/l were applied to fruit just at the start of ripening,
no respiration or chemical changes were induced (Dull
et al . 1967) showing that external application of ethylene
does not affect ripening.
Two key enzymes involved in the ethylene biosynthesis
pathway, 1-aminocyclopropane-1-carboxylate (ACC)
synthase (acacc-1) and 1-aminocyclo- propane-1-
carboxylate (ACC) oxidase (acaco-1), have been isolated
from pineapple fruit and characterized (Cazzonelli et al .
1998). These two enzymes catalyse the last two steps in
the ethylene biosynthesis pathway (Yang & Hoffman
1984). Both enzymes have been proven to be important
in the overall regulation of ethylene biosynthesis;
however, ACC synthase is established as the limiting
enzyme in the pathway (Kende 1993). Southern blot
analysis suggested the presence of only one copy of
acacc-1 and one or two copies of acaco-1 in the pineapple
genome. Expression of some acacc-1 was detected in
green pineapples and there was a 16-fold increase in the
level of acacc-1 in ripe fruit tissue. Unwounded leaf
tissue did not show any detectable levels of acacc-1,
whilst wounded tissue showed low levels of expression.
Northern blot analyses have shown the expression of
acaco-1 to be highly induced in wounded pineapple leaf
tissue and to a lesser extent in ripening fruit tissue. The
accumulation of ACC synthase and ACC oxidase mRNAs
during pineapple fruit ripening raises new questions
about the putative role of ethylene during nonclimacteric
fruit ripening (Cazzonelli et al . 1998).
The nonclimacteric pineapple fruit produces around
22 ml CO 2 kg −1 h −1 at 23°C, with no dramatic respiratory or
biochemical changes during ripening (Dull et al . 1967).
A decrease in the oxygen concentration to 2.5% resulted in
a decrease in respiratory rate. In contrast an increase in the
carbon dioxide concentration up to 10% had no detectable
effect on the respiration rate (Dull et al . 1967). Measurement
of carbon dioxide exchange and acid levels in detached
pineapple leaves indicated the presence of photorespiration
in pineapple (Moradshahi et al . 1977).
Presence of preformed chitinase activity, which is
usually considered to be an antifungal or anti-pest defence
mechanism, was shown in pineapple using chitinase
activity gel and immunoblot analysis by Taira et al .
(2005a). Of the three chitinases, Type A (acidic class III)
was found to exist in all tissues, while type B (weakly basic
class I, which has strong antifungal activity) and type C
(acidic class I) are localized mainly in the leaf and stem. In
a pericarp, Type A exists at all stages during fruit
development, while type B and type C exist only at the
early stage. Synthesis of type A is induced by ethylene,
while that of types B and C is not affected by it. These
results suggest that the physiological roles of these three
types of chitinase in pineapple are different. At low ionic
strength, PL Chi-B exhibits strong antifungal activity
toward Trichoderma viride while the others do not. At high
ionic strength, PL Chi-B and -C exhibit strong and weak
antifungal activity respectively. PL Chi-A does not have
antifungal activity (Taira et al . 2005b).
POST-HARVEST HANDLING
Changes in maturation stage are evident when peel colour
turns from green to yellow at the base of the fruit. Harvesting
maturity is often when the base of the fruit has changed
from green to yellow colour. Generally when 30-50% eyes
have turned yellow from the base, the fruit becomes ready
to harvest. Harvesting maturity of pineapple may also vary
depending on purpose and market destination. For remote
markets it is best to harvest slightly early when at the
10-20% yellow stage or even 100% green but mature stage,
just before these striking colour changes begin. External
colour of pineapple is an important trait in consumer pref-
erence. Consumers judge fruit quality by skin colour and
aroma. A minimal content of soluble solids of 12% and a
maximal acidity of 1% ensure a minimal level of consumer
acceptance along with size and texture uniformity, absence
of rotting, sunburns cracks, bruises, internal breakdown,
endogenous brown spot and damage by insects. A SSC:TA
ratio of 0.9 to 1.3 is normally recommended (Soler 1992).
Immature fruit should not be shipped, since they do not
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