Agriculture Reference
In-Depth Information
Unlike in non-seed tissues where ROS production is
increased by ABA, ABA reduced ROS production in imbibed
rice seeds, especially in the embryo region. Such reduced ROS
also led to an inhibition of ASC production. GA accumulation
was also suppressed by reduced ROS and ASC level, which
was indicated by the inhibited repression of GA biosynthesis
genes, amylase genes, and enzyme activity (Ye et al. 2011).
Pullulanase from seeds after 8 days of germination was
almost equal to that from non-germinating seeds, which
shows that these two enzymes are the same protein, starch
debranching enzyme also known as R-enzyme. Therefore,
the same pullulanase may play roles in both starch synthesis
during ripening and starch degradation during germination
in rice seeds.
Pullulanase in non-germinating seeds was compared
with that in germinating seeds. Moreover, pullulanase from
the endosperm of rice (
Oryza sativa
. Cv. Hinohikari) seeds
was isolated and its properties suggest that the PI value
of pullulanase from seeds after 8 days of germination was
almost equal to that from non-germinating seeds. The enzyme
was strongly inhibited by O-Cyclodextrin. The enzyme
was not activated by thiol reagents such as dithiothreotol, 2
mercaptoethanol or glutathione. The enzyme most preferably
hydrolysed pullulan and liberated only maltotriose. The
pullulan hydrolysis was strongly inhibited by the substrate
at a concentration higher than 0.1%. The degree of inhibition
increased with an increase in the concentration of pullulan.
However, the enzyme hydrolysed amylopectin, soluble starch
and beta limit dextrin more rapidly as their concentrations
increased. The enzyme exhibited a glucosyltransfer activity
and produced an a-1, 6 linked compound of two maltotriose
molecules from pullulan (Yamasaki et al. 2008).
