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Formation of chloroplast protrusions and catalase activity in alpine Ranunculus glacialis under elevated temperature and different CO2/O2 ratios

Buchner, Othmar, Moser, Tim, Karadar, Matthias, Roach, Thomas, Kranner, Ilse, Holzinger, Andreas
Protoplasma 2015 v.252 no.6 pp. 1613-1619
Ranunculus, alpine plants, ascorbate peroxidase, carbon dioxide, catalase, chloroplasts, hydrogen peroxide, irradiation, leaves, mesophyll, photorespiration, solar radiation, temperature
Chloroplast protrusions (CPs) have frequently been observed in plants, but their significance to plant metabolism remains largely unknown. We investigated in the alpine plant Ranunculus glacialis L. treated under various CO₂ concentrations if CP formation is related to photorespiration, specifically focusing on hydrogen peroxide (H₂O₂) metabolism. Immediately after exposure to different CO₂ concentrations, the formation of CPs in leaf mesophyll cells was assessed and correlated to catalase (CAT) and ascorbate peroxidase (APX) activities. Under natural irradiation, the relative proportion of chloroplasts with protrusions (rCP) was highest (58.7 %) after exposure to low CO₂ (38 ppm) and was lowest (3.0 %) at high CO₂ (10,000 ppm). The same relationship was found for CAT activity, which decreased from 34.7 nkat mg⁻¹ DW under low CO₂ to 18.4 nkat mg⁻¹ DW under high CO₂, while APX activity did not change significantly. When exposed to natural CO₂ concentration (380 ppm) in darkness, CP formation was significantly lower (18.2 %) compared to natural solar irradiation (41.3 %). In summary, CP formation and CAT activity are significantly increased under conditions that favour photorespiration, while in darkness or at high CO₂ concentration under light, CP formation is significantly lower, providing evidence for an association between CPs and photorespiration.