Agriculture Reference
In-Depth Information
stored starch and other nutrients in the endosperm are digested
by these hydrolases to small molecules that are taken up by the
embryo to support seedling elongation (Jacobsen et al. 1995).
Sugars transported to the embryo in turn repress alpha-amylase
expression and GA biosynthesis in the embryo (Perata et al.
1997). Another plant hormone, abscisic acid, antagonizes GA
action and represses the expression of alpha-amylase, providing
a mechanism for preventing precocious germination (Jacobsen
et al. 1995). Accordingly, the expression of alpha-amylase in
germinating cereals is subject to multiple modes of regulation
by sugars and hormones, induced by GA and sugar depletion
and repressed by sugars and abscisic acid (Perata et al. 1997,
Yu et al. 1996). Expression of α-amylase genes during cereal
germination and seedling growth is regulated negatively by
sugar in embryo and positively by GA in endosperm through
the sugar response complex (SRC) and the GA response
complex (GARC) respectively (Chen et al. 2006).
Cold temperature enhanced ABA synthesis which intern
retards alpha-amylase activity, levels of sucrose, reducing
sugars and total sugars. Suppression of RNase activity and
decrease in RNA content were observed (Fig. 5).
Sugar response
complex (SRC)
Suppression of
Sugar in embryo
α-Amylase
+
GA
3
in endosperm
GA response
complex
Retarded
α-Amylase
activity
Enhancement of
+
α-Amylase
+
Enhanced ABA
synthesis
induced by cold
Retards α-Amylase &
ABA in endosperm
other enzymes
Fig. 5
Cold infl uence on α-amylase activity.
