Characterization of the VFD cdka;1 mutant. (A–C) Comparison between a WT Arabidopsis plant (A), the cdka;1/− null mutant (B), and the cdka;1/− VFD mutant (C). The cdka;1/− VFD mutants are reduced in growth to a similar extent as the homozygous cdka;1 mutant but develop a root. (D) Upper row: CDK-kinase assays with plant material of WT, VF cdka;1/−, and VFD cdka;1/− using bovine histone H1 as a substrate. Lower row: CDKA;1 protein levels per kinase assay were visualized using an α-PSTAIRE antibody.