References

25 Hydro-Electrochemical Integration of the Higher Plant 377
Energy Charge [ NADPH 2/NADP ]
7
6
5
4
3
2
1
0
0.65
0.56
0
4.5 days 24 h various hours (0 - 72)
32.5°C / 10°C
20°C 20°C
12 24 36 48
Darkness [h]
[NADPH 2 / NADP]
[ATP] + 0.5 [ADP]
[ATP] + [ADP] + [AMP]
60 72
Fig.25.4. Circadian rhythm of NADPH2-to-NADP ratio and of “energy charge” of C. rubrum
seedlings. The seedlings were germinated in constant light and alternating conditions of
temperature for 4.5 days, thereafter transferred to constant 20 ◦ C for 24 h followed by a dark
period of varied duration (3-h increments) (Wagner et al. 1975)
1983, 1998). In C. rubrum there are semicircadian oscillations with specific
phasing in enzyme activities involved in glycolysis, photosynthesis and
respiration resulting in a circadian rhythm of adenylate energy charge and
redox state (Table 25.2, Fig. 25.4).
There is an inverse phase relationship between glyceraldehyde-3-phosphate
dehydrogenase (GPD) linked to photosynthesis (NADP-GPD) and the
enzyme linked to glycolysis (NAD-GDP) (Fig. 25.5). Adenylate kinase, a key
enzyme in energy dissipation displays circadian/semicircadian oscillations
in activity. The enzyme exists as isoenzymes in chloroplasts, mitochondria,
thecytoplasmandthenucleus.Theenzymeactivitiesaremodulatedby
light (phytochrome, cryptochrome), glucose feeding and photoperiod and
thermoperiod (Figs. 25.6–25.8).
The rhythm in enzyme activities may be amplitude-modulated by phytochrome.
The phytochrome action is gated by the phasing of the endogenous
rhythm reflecting a sequence of photophile and skotophile phases as
conceived by Bünning (1977) for the functioning of the physiological clock
(Figs. 25.9 and 25.10).