Diurnal Fluctuations in the Content and Functional Properties of the Light Harvesting Chlorophyll a/b Complex in Thylakoid Membranes

Abstract

Diurnal fluctuations were observed in the content and some structural and functional properties of the light-harvesting chlorophyll (Chi) a/b pigment-protein complex of photosystem 11 (LHCII) in young developing wheat (Triticum aestivum) leaves grown under 16 hours light/8 hours dark illumination regime. The fluctuations could be correlated with the diumal oscillation in the level of mRNA for LHCII. The most pronounced changes occurred in the basal segments of the leaves. They were weaker or hardly discernible in the middle and tip segments. As judged from the diurnal variations of the Chl-a/Chl-b molar ratio, the LHCII content of the thylakoid membranes peaked around 2 pm. This can be accounted for by the cumulative effect of the elevated level of mRNA in the morning and early afternoon. In the basal segment, the extent of the fluctuation in the LHCII content was approximately 25%, as determined from gel electrophoresis ("green gels"). The amplitude of the principal bands of the circular dichroism (CD) spectra of isolated chloroplasts paralleled the changes in the LHCII content. Our circular dichroism data suggest that the newly synthesized LHCII complexes are incorporated into the existing helically organized macrodomains of the pigmentprotein complexes or themselves form such macrodomains in the thylakoid membranes. Chl-a fluorescence induction kinetics also showed diumal variations especially in the basal segments of the leaves. This most likely indicates fluctuations in the ability of membranes to undergo "state transitions." These observations suggest a physiological role of diurnal rhythm of mRNA for LHCII in young developing leaves.The light-harvesting Chl a/b pigment-protein complex of PSII (LHCII3) is the predominant integral protein complex of 'This work was supported by grants OKKFT (Tt) 222/1988 and 56/1986 from the National Foundation of Technical Development (Hungary).

Low temperature interrupts circadian regulation of transcriptional activity in chilling-sensitive plants.

“…Indeed, we showed in earlier work on tomato that overnight chilling caused no measurable change in chlorophyll content, a/b ratio (8), or in the ability of illuminated leaves to activate Rubisco (30). The situation may be different in developing photosynthetic tissue since the level of accumulated Cab protein is low enough that diurnal oscillations in the chlorophyll a/b ratio are detectable (31). The responses of Cab and rca transcriptional activity in tomato to low temperature may be most significant as models for the behavior of other, much less abundantly expressed genes for which the interruption or mistiming in expression could have serious consequences for photosynthesis.…”

Acclimation of photosystem II in a cyanobacterium and a eukaryotic green alga to high and fluctuating photosynthetic photon flux densities, simulating light regimes induced by mixing in lakes

“…Almost all of the Chi b is contained within the light-harvesting antenna of PS II (e.g. Busheva et al, 1991). A high Chi a/b ratio when Z,,, = 2 Z,,,, can be interpreted as a decrease in the number of light-harvesting complexes of PS II (LHC II), despite the fact that conditions when Z,,, = 2 Z^,,, provided the lowest TDLD.…”

Tansley Review No. 37 Circadian rhythms: their origin and control

“…The polypeptide is then processed, the pigment synthesized and the pigment-protein complex incorporated into the thylakoid membrane. Busheva et al (1991) have shown that the content, and some of the structural and functional properties, of the light-harvesting Chi a/b pigment-protein complex in young wheat leaves show diurnal rhythmicity under light/dark conditions. These fluctuations are correlated with the diurnal rhythm in the level of the mRNA for the Chi a/b pigment-protein complex.…”