References

18 Oscillations in Plants 271
prehensively reviewed by Lüttge and Hütt 2004). Termed as “deterministic
chaos”, such behaviour is routine in many physical and hydrodynamics
systems. It still remains unclear, however, to what extent biological systems
functionally exploit this behaviour (Lüttge and Hütt 2004).
Experimental evidence on chaos in plants is only gradually accumulating.
The period doubling of leaf electric and temperature oscillations in
response to rhythmical light (Shabala et al. 1986, 1997b), aperiodic leaflet
movement reminiscent of homoclinic chaos (Chen et al. 1995) and chaotic
behaviour in CO2 exchange (Lüttge and Beck 1992) were reported. Chaotic
oscillations in the plant cell expansion rate were predicted by Kellershohn et
al. (1996), and bifurcational regimes in stomatal oscillations were modelled
by Rand et al. (1981).
Such a dearth of experimental evidence of deterministic chaos in plants
is more than surprising. Biological systems may gain benefits from exhibiting
chaotic dynamics as it may contribute to the generation of diversity
and hence adaptability (Lüttge and Hütt 2004). Advantages of chaotic dynamics
were recently discussed (Lloyd 1997) and include greater flexibility
in response towards external influences, phenotypic diversity, larger functional
independence from external entrainment and higher dissipation of
disturbance. Overall, exploitation of these benefits ensures the evolutionary
survival of chaotic dynamics; thus, it can make “chaotic” behaviour in
plants physiologically important.
18.3.4
Resonant Regimes
The Dictionary of Physics defines resonance as a “condition in which a vibrating
system responds with maximum amplitude to an alternating driving
force”. Resonance phenomena are widely used in various areas of modern
life (engineering, medicine, etc.). Keeping in mind the wide range of
oscillatory activity in plants, we have to answer two questions: (1) are resonant
responses possible in plants? and (2) will such behaviour be beneficial
to plants?
The answer to both questions is “yes”. There is no shortage of theoretical
models predicting resonant plant responses to periodical disturbance.
Examples include photosynthetic responses (Kocks and Ross 1995), membrane
transport activity (Markevich and Sel’kov 1986; Tsong 1990) and
energy transduction in glycolysis (Termonia and Ross 1982). These model
predictions are further confirmed by experimental studies showing the
resonant type of responses in stomatal conductance, water uptake and leaf
surface electric potential to rhythmical light (Shabala 1989, 1997; Cardon
et al. 1994) or root medium environment (Shabala et al. 1991). Preliminary