Temporal expression profiling of lipase during germination and rice caryopsis development.

Lipolytic enzymes play an important role in plant growth and development. In order to identify their
functional roles, the temporal expression profiling of lipase was carried out during rice seed germination,
growth and development of caryopsis. Changes in specific activities during germination revealed that the
lipolytic activity increased significantly until the end of germination. As the lipase activity increased, two
different lipase species were observed, which were designated as Lipase-I and Lipase-II based on their
relative mobility. Lipase-II was active during germination. Lipase-I was responsible for lipid mobilization,
a requirement for the growth of root and shoot. In comparison with the endosperm, the lipolytic activity
in roots was three fold higher. During rice caryopsis development, the lipolytic activity increased
gradually from initial panicle development and reached maximum as the grain dried to harvest maturity.
Quantitative real-time PCR analysis revealed that the Lipase-II was a stage specific expressing gene
during reproductive growth. The transcript level of Lipase-II reached maximum with completion of
germination, then decreased and remained stable during post-germinative growth. During caryopsis
development, Lipase-II is predominantly expressed in the developing seeds. The transcript abundance
increased gradually during initial stages of development and reached a maximum until seed maturation.
The results implicate that the dynamic changes in the enzyme activity of the two isoforms of lipase and
gene expression patterns are associated with the energy reserve mobilization during seed germination
and reproductive growth.