References

370 E. Wagner et al.
Table 25.1. Flowering of short-day plants (SDP) and long-day plants (LDP): essentials of the
photoperiodic reaction
SDP and LDP show opposite reactions to a given photoperiod
Reactions result from coincidence or non-coincidence of light and dark phases
of the photoperiod with corresponding phases of an endogeneous circadian rhythm
The main photoreceptors are the plant sensory pigment systems phytochrome
and cryptochrome
Circadian rhythm and phytochrome have the same properties in SDP and LDP
Critical photoperiodical induction produces irreversible changes in the leaves
of SDP and LDP leading to a common state both in SDP and in LDP
(proven by grafting experiments)
There is no difference between SDP and LDP in their response towards a common
inductor from a grafted leaf from an induced SDP or LDP
rhythmic kinetics of the stem extension rate (SER) and leaf movement (LM)
were investigated in the short-day plant Chenopodium rubrum and in the
long-day plant Chenopodium murale.
An undampened circadian rhythm in the SER was observed in continuous
light. Total stem elongation depends on the precise cooperation of stem
elongation of single internodes. In a specific experiment the first internode
completed growth while the second and the third internodes both contributedtothetotalSER.Thefractionofstemelongationduetothesecond
internode declined, while the growth rate of the third internode increased.
The two internodes thus displayed individual rhythms in the SER with the
same phasing and a reciprocal change in amplitude, precisely controlled
(Lecharny and Wagner 1984). As the stem grows, the internodes sustaining
the undamped circadian rhythm in the SER move up.
To observe whole plant behaviour time-lapse photography was used
showing rhythmic integration of the main shoot axis and side branches in
rhythmic growth as well as in LMs. The SER was continuously monitored
using an auxanometric system, while simultaneously analysing LM via
a video system. Changes in organ surface potential were investigated using
bipolar recordings with surface platinum electrodes (Fig. 25.1).
Cytoplasmic pH and Ca 2+ concentration at the apical meristem were
analysed using confocal laser-scanning microscopy and fluorescent dyes.
Rhythmic LMs in Chenopodium spp. do not depend on differential turgor
changes of flexor and tensor cells, as there are no pulvini at the basis of
the petioles, but they are due to the timing of differential growth at the
upper and lower surface of petioles and leaf basis. Detailed observation
of time lapse movies clearly shows that the rhythmic folding up of leaves
starts at the uppermost leaves surrounding the apical bud, progressing