Figure 2.

Cytokinin levels and activity in seedlings exposed to high CO₂. (a,b) Cytokinin (CK) levels in shoots and roots of Col-0 seedlings exposed to low and high CO₂. iP-type CK precursor levels (a) and tZ-type CK precursor levels (b) in shoots and roots are presented. (c) Expression levels of type-A ARR genes in Col-0 seedlings exposed to low and high CO₂. Transcript levels of ARR4, ARR6, and ARR15 were analysed by quantitative RT-PCR. Expression levels were normalized using At4g34270 as an internal control. Twelve-day-old seedlings grown on 1/2 MS agar plates at 280 ppmv were exposed to 280 ppmv (280) or 780 ppmv (780) CO₂ for the indicated periods. Error bars represent standard deviations of three biological replicates. Asterisks indicate statistically significant differences between 280 ppmv CO₂- and 780 ppmv CO₂-treated samples at the same exposure time (*p < 0.05; **p < 0.01; Student’s t-test). FW, fresh weight; tZ, trans-zeatin; iP, N⁶-(∆²-isopentenyl)adenine. The concentrations of cytokinin molecular species are shown in Supplementary Table S2.