Agriculture Reference
In-Depth Information
DAG = Days after germination
Dry rice seeds contain more than 17,000 stored mi RNAs. The
RNA-binding proteins perform important role in keeping the
stability and regulating the junctions of those long lived mi
RNAs.
The presence of adequate level of the Gibberellic acid (GA3)
in the seeds stimulated the synthesis, activation and secretion of
hydrolytic enzymes mainly alpha-amylase, releasing reducing
sugars and amino acids which are essentials for embryo growth
(Mayer and Poljakoff-Mayber 1989).
During cereal seed germination, alpha-amylase in the
aleurone layer plays an important role in hydrolyzing the
endosperm starch into metabolisable sugars, which provide
the energy for growth of roots and shoots (Akazawa and Hara-
Mishimura 1985, Beck and Ziegler 1989). Previous physiological
and biochemical studies have revealed that alpha-amylase
expression in the aleurone layer occurs as follows. First, active
gibberellins (GA) biosynthesis commences in the embryo, and
the GAs transported from the embryo to the aleurone layer
(Fincher 1989). Active GA s trigger the expression of alpha-
amylase at the transcriptional level through the induction of a
positive transactivating factor for alpha-amylase transcription
(Gubler et al. 1995). The alpha-amylase is secreted from the
aleurone layer into the endosperm to catalyse the hydrating
reaction of stored starch (Fig. 4).
Amylase activity increased as a result of germination and
on the 8th day both total activity and specifi c activity reached
the maximum. Temperature-activity profi le of
in vitro
analysis
of germinating rice seed alpha amylase indicates the optimal
temperature at 65ºC, but at 10ºC the relative activities is
20%. Thus at cold temperature the activity of alpha-amylase
decreased appreciably (Shaw and Chuang 1982).
