Formation of chloroplast protrusions and catalase activity in alpine Ranunculus glacialis under elevated temperature and different CO(2)/O(2) ratios

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 CO(2) concentrations if CP formation is related to photorespiration, specifically focusing on hydrogen peroxide (H(2)O(2)) metabolism. Immediately after exposure to different CO(2) 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 CO(2) (38 ppm) and was lowest (3.0 %) at high CO(2) (10,000 ppm). The same relationship was found for CAT activity, which decreased from 34.7 nkat mg(−1) DW under low CO(2) to 18.4 nkat mg(−1) DW under high CO(2), while APX activity did not change significantly. When exposed to natural CO(2) 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 CO(2) concentration under light, CP formation is significantly lower, providing evidence for an association between CPs and photorespiration. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00709-015-0778-5) contains supplementary material, which is available to authorized users.