Agriculture Reference
In-Depth Information
CO
2
in the atmosphere. Between 30 and 80% of the CO
2
taken
up by photosynthesis (P) each day is subsequently respired.
One of the most important environmental parameters
affecting rates of plant R is temperature. It is often assumed
that the relationship between plant R and temperature is
exponential with a constant Q
10
(about 2). The importance of
understanding variability in the Q
10
is highlighted by predicted
changes in the amplitude of diurnal temperatures experienced
by plants (Fig. 30).
The reduction in chlorophyll content has been implicated
to metabolic blocks in the porphyrin pathway that leads to
chlorophyll synthesis. Low temperature stress also affects
enzymes that carry out photosynthetic processes in the plant.
Because enzymes that are routinely involved in photosynthesis
have little energy, the rate of photosynthesis is slowed down
under low temperature. Satake and Hayase (1970) observed
higher cytological and histological disorders in the anthers of
cold stressed rice plants as compared to non-stressed plants.
Cold temperature stress at reproductive stage has also been
reported to cause fl ower abscission, pollen sterility, pollen
tube distortion, ovule abortion and poor seed set. Structural
and functionalities in the reproductive organs of cold-stressed
plants and failed fertilization or premature abortion of the
embryo have been observed.
The fl ower of rice diverged from those of model edicot
species such as Arabidopsis, etc. and is thus of great interest
in developmental and evolutionary biology. Specific to
grass species including rice, are the structural units of the
infl orescence called the spikelet and fl oret, which comprise
grass-specific peripheral organs and conserved sexual
organs. Recent advances in molecular genetic studies have an
