Agriculture Reference
In-Depth Information
Before chilling 30°C, chilling at 5°C of fl ag leaf at milky
dough stage and 50 Klux.
Mature storage tissues such as cereal endosperm consist
primarily of starch and a minor pool of soluble sugar.
Consequently, the major fate of translocated photosynthate
entering the developing endosperm is to be metabolized
by invertase or sucrose synthase into precursors for starch
biosynthesis. The endosperm sucrose pool represents an
alternative storage from the increasing photosynthate. It is
unclear whether endosperm sucrose accumulation depends
on transport of unmetabolized sucrose into endosperm cell or
whether resynthesis of sucrose occurs from a pool of hexoses
and nucleotide sugars common to the starch biosynthesis
pathway (Smyth and Prescott 1989).
Resynthesis of sucrose might be catalyzed by sucrose
synthase and sucrose phosphatase activities. The presence of
sucrose phosphate synthases in many storage organs suggests
that some sucrose may be resynthesized using the nonreversible
pathway.
ADP glucose pyrophosphorylase (AGP) and sucrose
synthase (SS) are important enzymes in starch biosynthesis
pathway of rice endosperm (Fig. 34). It is hypothesized that
difference in individual grain weight among rice cultivars or
within a cultivar is directly related to the variation in activities
of these enzymes and hormonal manipulation of enzyme
activities can enhance grain yield. One potential mechanism
for yield increases is that reduction of ethylene concentration at
anthesis which may improve assimilate partitioning to grains
and increases its weight. In an experiment, three indica rice
cultivars differing in grain size and weight were grown in the
fi eld conditions during dry season. Dry matter growth, rate of
division of endosperm cells, starch and sugar concentrations
