Submergence or water logging impose

Submergence or water logging imposes a
complex abiotic stress on rice plant, affects
numerous physiological and metabolic processes
(Sarkar et al., 2006; Bailey-Serres and Voesenek,
2008; Jianxiong et al., 2010 ). Deepwater rice
responds to partial submergence to complete
submergence by enhancing cell division and
elongation in the internodal regions of underwater
stems and rapid cell expansion is necessary for fast
elongation under flooding and low-oxygen stress
(Rose-John and Kende, 1984; Kende et al., 1998). In
this experiment the three cultivars responded
differently to submergence in terms of survival and
elongation. Ninety percent of FR 13A plants
survived after 8d of submergence in comparison
with less than 20 % in Sabita and 15 % in IR42 (data
not shown). Plant height increased due to
submergence in all the cv. (Table 1) but the
elongation was greater in Sabita and IR42 compared
to FR13A. After 8 d of submergence, the increase in
plant height was more than 98 % and 95 % in Sabita
and IR42 respectively whereas FR13A only
increased by 34 %.
The levels of cellulose content in rice shoot were
not significantly different among tolerant and
susceptible rice cv. under control condition.
Submergence significantly decreased the cellulose
content in susceptible IR42 cv. as compared to air
grown control plants but in FR13A and Sabita the
cellulose content was not significantly changed
(Table 1). Similarly the hemicelluloses content also
significantly decreased under submergence in all
the rice cv. studied compared to the control plant
but the reduction was more pronounced in
susceptible cv. IR42 (39 %) than Sabita (26 %) and
FR13A (21 %). Lignin content in rice shoot was
significantly more in susceptible cv. IR42 in
compared to FR13A and Sabita and was significantly
decreased due to submergence in all the cvs. (Table
1). The decreased was more pronounce in IR42 (30
%) than that of FR13A and Sabita (17 %). Internodes
of deep water rice are induced to elongate rapidly