Fig. 1.

Experimental set-up for determining the effect of different CO₂ concentrations on the formation of chloroplast protrusions (CPs) in leaves of R. glacialis. On 15 August 2013, a potted plants (n = 5) were placed inside cylindrical exposure chambers made of highly transparent Plexiglas and exposed to natural solar irradiation with the exception of (3) which was kept in darkness. During the 2.5 h exposure, air with different CO₂ concentrations was streamed through the chambers. 1 10,000 ppm, 2 38 ppm, while 3 and 4 had normal CO₂ concentration (380 ppm). b Mean leaf temperature (red line; n = 16) and photosynthetically active photon flux density (PPFD; black line) for the whole duration of the exposure. c Typical CPs in leaf mesophyll of R. glacialis immediately after the 2.5 h exposure at 38 ppm CO₂ and at natural solar irradiation. The DIC microscopy image clearly shows CPs as broad and beak-like, stroma-filled extensions of the chloroplast envelope. d Schematic drawing of c; light blue areas indicate CPs. Horizontal bars 2 μm