Rhythmical behaviour
is a quintessential pattern of life itself. Biological oscillations kept many generations of scientists
fascinated, from such diverse areas of knowledge as physiology, biochemistry, biophysics, mathematics, and
biological cybernetics. An avalanche-like increase in publication number led to foundation of several
specialised journals on biological rhythms. However, plants have always been treated as
“Cinderellas” in studies on biological rhythms. In contrast to quite obvious circadian rhythms
(with 24 h period), ultradian oscillations (with periods of minutes) are not as widespread in plants as they
are in animal organisms, at least at first glance. With a possible exception of plant movements (such as
leaves or plant axial organs) and oscillations in stomatal aperture, many plant physiologists treat
oscillations as some unwanted “noise”. More recently, a breakthrough in understanding of the
signalling role of Ca2+ in cell metabolism caused a vivid interest in calcium oscillations in
stomatal guard cells, as reflected by a large number of excellent reviews [1-3]. The physiological role of
ultradian oscillations in other plant tissues and organs is still underestimated. In this review, an attempt
is made to summarise the recent progress in this area and highlight the paramount role of oscillatory
processes in plant life. First, advantages and principles of oscillatory control are considered in the context
of plant physiology, with a major emphasis on feedback control and self-sustained oscillations, as well as on
determenistic chaos and “strange” behaviour in plants. Next, a possible role for ultradian rhythms
in timekeeping and the link between ultradian and circadian oscillators is discussed. Several models of
circadian oscillators are analysed, and various pros - and contras - for each of them are
discussed. The major emphasis is made on possible role of cellular membranes as an important component of the
feedback loop in circadian clock mechanism. The importance of membrane- related oscillations is further
illustrated by their crucial role as a part of the encoding mechanism, mediating plant-environmental
interaction. Practical examples include cell differentiation and morphogenesis, growth, development and
adaptive responses to various abiotic and biotic stresses.
- Trewavas A (1999) Plant
Physiology 120: 1-6
- Blatt MR (2000) Current Opinion in Plant
Biology3: 196-204
- Webb AAR (2003) New
Phytologist160: 281-303
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