Seed Germination and Root Elongation Assays

After surface sterilization of the seeds, 70 seeds of each genotype were sowed on 1/2 MS plates supplemented with ABA. Stratification was conducted in the dark at 4°C for 3 d. Radical emergence was recorded at the indicated times. At 6 d, seedlings with expanded green cotyledons were scored as the percentage of seeds. For root elongation assays, seeds were stratified for 3 d in the dark at 4°C (for experiments including abi1abi2hab1pp2ca quadruple mutant, all seeds were stratified for 10 d), sown, and grown on vertically oriented 1/2 MS plates for 4 d. Twenty seedlings with similar primary root length were transferred onto new 1/2 MS plates lacking or supplemented with the indicated concentrations of ABA. The plates were scanned after 6 d of growth, and primary root lengths were measured with ImageJ (http://imagej.nih.gov/ij/download.html).