Agriculture Reference
In-Depth Information
8.2 Genetic Engineering Approach
C
4
crops can assimilate more CO
2
than that of C
3
crops due to specialized C
4
me-
tabolism cycle and can reduce photorespiration by 80 % by increasing bundle
sheath CO
2
level significantly (Kajala et al.
2011
). In recent times, installation of
C4 mechanism into staple food crops like rice, wheat and potato is considered as
the futuristic answer to the problem of increasing food insecurity in today's world.
International C4 Consortium led by International Rice Research Institute (IRRI)
has been trying to install two-cell C4 cycle in rice for achieving higher productivity
and higher resource utilization efficiency. This task itself is an enormous challenge
to the scientific community, however the conversion is not impossible as all C4
cycle enzymes are found in C3 plants at low level and no new genes are associated
with C4 pathway (Sage
2004
; Brown et al.
2010
). The aim of such a research is to
down-regulate the expression of mesophyll cells and change the leaf anatomy i.e.,
increased vein density and number of M cells in between veins as low as possible.
This feature of the C4 rice would help reduce emission of methane as M cells play
an important role in determining the methane conductance through the rice plant.
8.3 Temperature Regulation
Various studies have reported a positive correlation between CH
4
flux and soil tem-
perature (Conrad et al.
1989
; Sass et al.
1991
) but no significant relation is found
between methane emissions and amount of light incident on the rice plant (Nouchi
et al.
1990
). Gas permeability of root epidermal layers and structure of aerenchyma
gets adversely affected by aging (Armstrong
1971
; Arikado et al.
1990
). At maturity,
CH
4
emission is reduced due to choking of aerenchyma but increased air temperature
during maturation of crop does not play any significant role (Watanabe et al.
1994
).
Hosono et al. (
1997
) reported the effect of temperature on the rate of CH
4
emis-
sion. Their study showed that when temperature was increased from 15 to 30 °C,
the methane diffusion increased by 2-2.2 times. The study also suggested that air
temperature has much less effect on CH
4
conductance than that of rhizosphere soil
temperature. The correlation between soil temperature and conductance was report-
ed to be statistically significant (
p
< 0.01). At 28 °C soil temperature, conductance
was six times higher than that of at 18 °C.
8.4 Water Management
It has been reported that the degree of water submergence could influence the rate of
methane flux from rice plants (Wang et al.
1993
). Wang et al. (
1997a
) have studied
