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Characterization of the influence of chlororespiration on the regulation of photosynthesis in the glaucophyte Cyanophora paradoxa

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ABSTRACT

Glaucophytes are primary symbiotic algae with unique plastids called cyanelles, whose structure is most similar to ancestral cyanobacteria among plastids in photosynthetic organisms. Here we compare the regulation of photosynthesis in glaucophyte with that in cyanobacteria in the aim of elucidating the changes caused by the symbiosis in the interaction between photosynthetic electron transfer and other metabolic pathways. Chlorophyll fluorescence measurements of the glaucophyte Cyanophora paradoxa NIES-547 indicated that plastoquinone (PQ) pool in photosynthetic electron transfer was reduced in the dark by chlororespiration. The levels of nonphotochemical quenching of chlorophyll fluorescence was high in the dark but decreased under low light, and increased again under high light. This type of concave light dependence was quite similar to that observed in cyanobacteria. Moreover, the addition of ionophore hardly affected nonphotochemical quenching, suggesting state transition as a main component of the regulatory system in C. paradoxa. These results suggest that cyanelles of C. paradoxa retain many of the characteristics observed in their ancestral cyanobacteria. From the viewpoint of metabolic interactions, C. paradoxa is the primary symbiotic algae most similar to cyanobacteria than other lineages of photosynthetic organisms.

No MeSH data available.


The effect of ionophore (nigericin) on chlorophyll fluorescence kinetics.After 2.5 min from turning on of red actinic light (solid upward arrow), saturating light was applied to obtain first Fm’. Soon after, ethanol for mock control (A) or nigericin (final concentration at 10 μM in the panel B experiment or at 50 μM in the panel C experiment) was added. After the level of fluorescence settled down to the steady state (Fs), saturating light was applied to obtain second Fm’. Then, red actinic light temporary turned off (solid downward arrow), and DCMU was added (thin upward arrow). Finally, red actinic light was turned on again and bring the cells to State 1 for the determination of Fm.
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f4: The effect of ionophore (nigericin) on chlorophyll fluorescence kinetics.After 2.5 min from turning on of red actinic light (solid upward arrow), saturating light was applied to obtain first Fm’. Soon after, ethanol for mock control (A) or nigericin (final concentration at 10 μM in the panel B experiment or at 50 μM in the panel C experiment) was added. After the level of fluorescence settled down to the steady state (Fs), saturating light was applied to obtain second Fm’. Then, red actinic light temporary turned off (solid downward arrow), and DCMU was added (thin upward arrow). Finally, red actinic light was turned on again and bring the cells to State 1 for the determination of Fm.

Mentions: Apparently the main cause of the chlorophyll quenching was not energy dependent quenching but state transition. This assumption was further tested by the addition of an ionophore, nigericin, under high red light condition. After the addition of nigericin (10 or 50 μM) under strong red actinic light (562 μmol m−2 s−1), the level of Fm’ was only slightly affected even though the level of Fs gradually increased (Fig. 4B,C). The calculated NPQ in the presence of 10 μM nigericin (0.338 ± 0.030) was not significantly different from that before the addition of nigericin (0.406 ± 0.033) or that in the presence of mock control (ethanol) (0.361 ± 0.034). Thus, the low level of Fm’ under strong light for several minutes could be fully ascribed to state transition, not to energy-dependent quenching, similarly to the case of Fm’ in the dark presented in Table 1.


Characterization of the influence of chlororespiration on the regulation of photosynthesis in the glaucophyte Cyanophora paradoxa
The effect of ionophore (nigericin) on chlorophyll fluorescence kinetics.After 2.5 min from turning on of red actinic light (solid upward arrow), saturating light was applied to obtain first Fm’. Soon after, ethanol for mock control (A) or nigericin (final concentration at 10 μM in the panel B experiment or at 50 μM in the panel C experiment) was added. After the level of fluorescence settled down to the steady state (Fs), saturating light was applied to obtain second Fm’. Then, red actinic light temporary turned off (solid downward arrow), and DCMU was added (thin upward arrow). Finally, red actinic light was turned on again and bring the cells to State 1 for the determination of Fm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384210&req=5

f4: The effect of ionophore (nigericin) on chlorophyll fluorescence kinetics.After 2.5 min from turning on of red actinic light (solid upward arrow), saturating light was applied to obtain first Fm’. Soon after, ethanol for mock control (A) or nigericin (final concentration at 10 μM in the panel B experiment or at 50 μM in the panel C experiment) was added. After the level of fluorescence settled down to the steady state (Fs), saturating light was applied to obtain second Fm’. Then, red actinic light temporary turned off (solid downward arrow), and DCMU was added (thin upward arrow). Finally, red actinic light was turned on again and bring the cells to State 1 for the determination of Fm.
Mentions: Apparently the main cause of the chlorophyll quenching was not energy dependent quenching but state transition. This assumption was further tested by the addition of an ionophore, nigericin, under high red light condition. After the addition of nigericin (10 or 50 μM) under strong red actinic light (562 μmol m−2 s−1), the level of Fm’ was only slightly affected even though the level of Fs gradually increased (Fig. 4B,C). The calculated NPQ in the presence of 10 μM nigericin (0.338 ± 0.030) was not significantly different from that before the addition of nigericin (0.406 ± 0.033) or that in the presence of mock control (ethanol) (0.361 ± 0.034). Thus, the low level of Fm’ under strong light for several minutes could be fully ascribed to state transition, not to energy-dependent quenching, similarly to the case of Fm’ in the dark presented in Table 1.

View Article: PubMed Central - PubMed

ABSTRACT

Glaucophytes are primary symbiotic algae with unique plastids called cyanelles, whose structure is most similar to ancestral cyanobacteria among plastids in photosynthetic organisms. Here we compare the regulation of photosynthesis in glaucophyte with that in cyanobacteria in the aim of elucidating the changes caused by the symbiosis in the interaction between photosynthetic electron transfer and other metabolic pathways. Chlorophyll fluorescence measurements of the glaucophyte Cyanophora paradoxa NIES-547 indicated that plastoquinone (PQ) pool in photosynthetic electron transfer was reduced in the dark by chlororespiration. The levels of nonphotochemical quenching of chlorophyll fluorescence was high in the dark but decreased under low light, and increased again under high light. This type of concave light dependence was quite similar to that observed in cyanobacteria. Moreover, the addition of ionophore hardly affected nonphotochemical quenching, suggesting state transition as a main component of the regulatory system in C. paradoxa. These results suggest that cyanelles of C. paradoxa retain many of the characteristics observed in their ancestral cyanobacteria. From the viewpoint of metabolic interactions, C. paradoxa is the primary symbiotic algae most similar to cyanobacteria than other lineages of photosynthetic organisms.

No MeSH data available.