Fig. 4.

Aniline blue staining for plasmodesmal callose in the first and the third leaves of 18-day-old A. thaliana plants grown under a 390 p.p.m. (control) or a 780 p.p.m. (experimental) atmospheric CO₂ concentration. Z-stacked confocal images of vein cells in the midrib of the first leaves (A, B) and the third leaves (C, D) of the control and experimental plants. (A) Control plants grown under a 390 p.p.m. CO₂ atmosphere. (B) Experimental plants grown under a 780 p.p.m. CO₂ atmosphere. Asterisks indicate sieve plates. SE, sieve element; CC, companion cell. Scale bars = 10 µm.