Circadian expression of the light-harvesting protein of Photosystem II in etiolated bean leaves following a single red light pulse: Coordination with the capacity of the plant to form chlorophyll and the thylakoid-bound protease

Abstract

The appearance of the light harvesting II (LHC II) protein in etiolated bean leaves, as monitored by immunodetection in LDS-solubilized leaf protein extracts, is under phytochrome control. A single red light pulse induces accumulation of the protein, in leaves kept in the dark thereafter, which follows circadian oscillations similar to those earlier found for Lhcb mRNA (Tavladoraki et al. (1989) Plant Physiol 90: 665-672). These oscillations are closely followed by oscillations in the capacity of the leaf to form Chlorophyll (Chl) in the light, suggesting that the synthesis of the LHC II protein and its chromophore are in close coordination. Experiments with levulinic acid showed that PChl(ide) resynthesis does not affect the LHC II level nor its oscillations, but new Chl a synthesis affects LHC II stabilization in thylakoids, implicating a proteolytic mechanism. A proteolytic activity against exogenously added LHC II was detected in thylakoids of etiolated bean leaves, which was enhanced by the light pulse. The activity, also under phytochrome control, was found to follow circadian oscillations in verse to those in the stabilization of LHC II protein in thylakoids. Such a proteolytic mechanism therefore, may account for the circadian changes observed in LHC II protein level, being implicated in pigment-protein complex assembly/stabilization during thylakoid biogenesis.

Expression studies in tetrapyrrole biosynthesis: inverse maxima of magnesium chelatase and ferrochelatase activity during cyclic photoperiods

“…In another experimental system using other plant species the chlorophyll-synthesizing capacity parallels the cycling rate of ALA synthesis (Beator et al 1992;Beator and Kloppstech 1993;Bei-Paraskevopoulou et al 1995). A simultaneous activation of Mg-chelatase would tentatively ensure the supply of Mg-porphyrins.…”

Etioplast and etio-chloroplast formation under natural conditions: the dark side of chlorophyll biosynthesis in angiosperms

“…From the dynamic point of view that implies that Chl and host protein productions have to be coordinated (Apel and Kloppstech 1980;Plumley and Schmidt 1995). Indeed these processes are controlled by phytochrome through the circadian clock (Bei-Paraskevopoulou et al 1995;Matsumoto et al 2004; McCormac and Terry 2002b) (Fig. 5).…”

Thylakoid-bound proteolytic activity against LHC II apoprotein in bean

“…This suggests that the protease activity in thylakoids is also under control of the biological clock. The oscillations observed in the proteolytic activity of the isolated primary thylakoids were found to be of opposite sign to those earlier described for the appearance of the LHC II protein in LDS-solubilized total leaf protein extracts and the capacity of the plant to form Chl in the light (Bei-Paraskevopoulou et al 1995).…”

“…V/a such cation concentration changes, Pfr may similarly affect the oscillations in the degrading activity of thylakoids obtained from etiolated leaves following a Red light pulse. Phytochrome is believed to synchronize the biological clock in etiolated bean leaves, and to affect circadian oscillations in LHC II mRNA, capacity for Chl synthesis and stabilization of the LHC II protein in total leaf extracts (Tavladoraki et al 1989;Argyroudi-Akoyunoglou et al 1991;BeiParaskevopoulou and Argyroudi-Akoyunoglou 1991;Bei-Paraskevopoulou et al 1995). How this synchronization occurs is unknown.…”

“…How this synchronization occurs is unknown. It is possible that oscillations in Ca + + concentrations, induced by phytochrome photoreception, may result in oscillations of the protease binding, and thus in oscillations of the LHC II level in thylakoids (Bei-Paraskevopoulou et al 1995). Further work is under way to elucidate this point.…”