Root elongation assay

Seeds from transgenic and wild type lines were prepared and platted on 0.5× MS media. After stratification, plates were oriented vertically in 24-h light for 5 days. Seedlings were subsequently transferred to hormone-, BCAA-, metabolite- or herbicide-supplemented 0.5× MS media containing 3% (w/v) sucrose and 0.6% (w/v) agar to promote root growth. Root tips were marked on the base of the plate and the seedlings were grown vertically in constant light for an additional 5 days. Root elongation was measured and compared to growth on standard 0.5× MS media containing 3% (w/v) sucrose and 0.6% (w/v) agar plate.