Abstract
Oxygenation of ribulose-1,5-bisphosphate catalyzed by Rubisco produces glycolate-2-P. The photorespiratory pathway, which consists of photorespiratory carbon and nitrogen cycles, metabolizes glycolate-2-P to the Calvin cycle intermediate glycerate-3-P and is proposed to be important for avoiding photoinhibition of photosystem II (PSII), especially in C3 plants. We show here that mutants of Arabidopsis (Arabidopsis thaliana) with impairment of ferredoxin-dependent glutamate synthase, serine hydroxymethyltransferase, glutamate/malate transporter, and glycerate kinase had accelerated photoinhibition of PSII by suppression of the repair of photodamaged PSII and not acceleration of the photodamage to PSII. We found that suppression of the repair process was attributable to inhibition of the synthesis of the D1 protein at the level of translation. Our results suggest that the photorespiratory pathway helps avoid inhibition of the synthesis of the D1 protein, which is important for the repair of photodamaged PSII upon interruption of the Calvin cycle.
Highlights
Oxygenation of ribulose-1,5-bisphosphate catalyzed by Rubisco produces glycolate-2-P
When wild-type and photorespiratory pathway mutants that impair Fd-GOGAT, Ser hydroxymethyltransferase (SHMT), DiT2, and glycerate kinase (GLYK) (Fig. 1) were grown in high CO2 (0.6% CO2 in air), there was no significant difference in chlorophyll concentration between wild type and any photorespiratory pathway mutants, the chlorophyll a/b ratio was slightly lower in all photorespiratory pathway mutants
The presence of chloramphenicol suppressed the recovery of the level of Fv/Fm and completely abolished the differences of it between wild type and photorespiratory pathway mutants at both 40 mmol photons m22 s21 and 200 mmol photons m22 s21. These results indicate that impairment of the photorespiratory pathway suppresses the protein synthesisdependent repair of photodamaged photosystem II (PSII) in high light but not in low light in air
Summary
Oxygenation of ribulose-1,5-bisphosphate catalyzed by Rubisco produces glycolate-2-P. It is initiated by the oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco; Ogren and Bowes, 1971; Ogren, 1984) In this reaction, glycolate-2-P is produced and subsequently metabolized in the photorespiratory carbon cycle to form the Calvin cycle intermediate, glycerate-3-P (Ogren, 1984; Leegood et al, 1995). We conclude that the photorespiratory pathway minimizes photoinhibition by facilitating the repair process (avoiding suppression of the repair of photodamaged PSII) but not by suppressing the photodamage process
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