References

18 Oscillations in Plants 269
The foundations of the systems theory suggestthatiftherelationship
between several parameters within the system is described by linear equations,
such a system should eventually reach its stable state (Stucki and
Somogyi 1994). Once disturbed, such a system will eventually return to
a new steady state through a series of damped oscillations. This is often observed
for plant photosynthetic responses (Kocks and Ross 1995), changes
in stomatal aperture (Barrs 1971) or cell electrophysiological characteristics
(Tyerman et al. 2001).
The story is quite different if the system is governed by non-linear mechanisms.
In that case, a limited cycle (a two-dimensional attractor), rather
than a singular point, will be a stable condition (Stucki and Somogyi 1994).
Thus,self-sustainedoscillationsareexpectedtobefoundinsuchnon-linear
systems.
Thereisnodoubtthatmostphysiologicalprocessesinplantsaregoverned
by non-linear mechanisms. Physiologically it means that within some
narrow range of parameters (light intensity, ambient temperature, water
and nutrient availability, etc.), plant responses might be linear. In this
case, a sudden perturbation within this range will cause only a brief series
of damped oscillations in plant physiological responses. As soon as
the disturbance is beyond the range of the linear response, non-damping
self-sustained oscillations are expected.
18.3.2
Advantages of Oscillatory Strategy
Every plant physiologist will probably agree that circadian rhythmicity
in plants is a result of evolutionary adaptation of energy metabolism to
optimise energy conservation with respect to daily environmental cycles of
energy supply (Wagner et al. 1975). Researchers are less in agreement when
discussing the functional role of ultradian oscillations in plants. Although
there is no lack of theoretical investigations (see later) showing advantages
of oscillatory strategy, direct evidence for plants is still rather rudimentary.
Earlier Rapp (1987) described at least five positive functional advantages
which periodic behaviour confers to living organisms. These are revisited
next.
18.3.2.1
Temporal Organisation
Separate temporal compartments may be necessary where mutually incompatible
biochemical reactions occur in an identical spatial (subcellular)
compartment. Examples may include protein synthesis and degradation.