Agriculture Reference
In-Depth Information
storage tissue of a turgid, fully developed leaf from a fi eld-grown plant
occupies about half the leaf cross section at the middle of the blade. This tissue
becomes narrower as moisture stress increases. This tissue is absent towards
the tip and margins.
Carbon is assimilated in pineapple leaves by the Crassulacean acid
metabolism (CAM) pathway. The principal features of this pathway are large
diurnal fl uctuations in organic acids, mainly malic, and an inverted pattern
of gas exchange due to the fi xation of CO 2 into malate at night and its release
and reduction to carbohydrate during the day (Malezieux et al. , 2003). The
inverted pattern of gas exchange is the result of changes in the intercellular
CO 2 concentration. At night the CO 2 acceptor molecule phosphoenolpyruvic
acid (PEP) is produced using stored carbohydrate. The PEP is carboxylated
to form oxaloacetic acid, which is then reduced to form malate. The malate
is transported to the cell vacuole, where it is stored until the following day.
Shortly after sunrise, malic acid moves from the vacuole to the cytoplasm, is
decarboxylated to produce a molecule of CO 2 and a molecule of pyruvic acid;
the low intercellular CO 2 level begins to increase and the stomata soon close.
In the morning to early afternoon hours, the released CO 2 is fi xed and reduced
to carbohydrate by normal Calvin cycle or C-3 photosynthesis. As the malic
acid level declines, the intercellular CO 2 level also decreases and the stomata
open. During the remainder of the afternoon hours, CO 2 is assimilated from
the atmosphere by conventional C-3 photosynthesis. Normal night opening of
pineapple stomata requires sunlight on the previous day.
In fl orescence and fl ower
The infl orescence is terminal (Fig.12.1), developing from the apical meristem
of the plant. Peduncle elongation begins at the time reproductive development
is initiated and continues after fl ower formation. The fi rst sign of fl oral
initiation, whether natural or induced, is a rapid increase in diameter of the
apical meristem, and 5-6 days after this change takes place, the peduncle
begins to elongate. It continues to elongate as the infl orescence develops.
The infl orescence can consist of up to 200 individual trimerous fl owers with
a phyllotaxy of 21/55 for large fruits of 'Smooth Cayenne' and 13/34 for
smaller ratoon crop fruit (Ekern, 1968). Individual fl owers are composed of
three sepals, three petals, six stamens and a tricarpellate ovary. One to several
fl owers open each day over a period of 3-4 weeks, starting from the base of
the infl orescence (Okimoto, 1948). The fruitlets develop from fl owers that do
not abscise and each fl ower is subtended by a fl eshy bract (Fig. 12.1). The style,
stamens and petals wither and the remaining fl oral parts develop into the
fruitlet (Okimoto, 1948). The ovules and pollen grains are functional but seeds
are not normally formed as 'Smooth Cayenne' is strongly self-incompatible.
 
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