Kinematic Analysis
The kinematic analysis was performed according to Sprangers et al. (2016). It includes measurements of leaf length, cell length profile along the leaf axis, calculation of leaf elongation rate and estimation of the size of the leaf basal meristem. Leaf length was measured daily with a ruler on the fifth leaf from the moment it was visible among the older leaves. LER was calculated for the first 3 days of its growth as the difference in length divided by the time difference between successive measurements. For meristem measurements, samples harvested 3 days after leaf emergence were analyzed by fluorescence microscopy (AxioScope A1, Axiocam ICm1, Zeiss, Germany) at 20× magnification. The size of the meristematic zone of the leaf was estimated by locating the most distal mitosis in the cell files. Cell length was measured by light microscopy (AxioScope A1, Axiocam ICm1, Zeiss, Germany) using differential interference contrast at 40× magnification and the online measurement module in the Axiovision software (Zeiss, Germany). The leaf growth zone was split in ten 1cm-long- segments and cell length measurements were carried out at four locations in each segment: at the tip (0 cm), at one-third of the segment (0.3 cm), at two-thirds (0.6 cm), and at the end of the segment (0.99 cm). Around 20 cells were measured at each location. The raw data obtained for individual leaves were smoothed and interpolated at an interval of 50 mm using the kernel-smoothing function locpoly of the KernSmooth package (Wand and Jones, 1995) for the R statistical software environment (R Core Team, 2011; https://www.R-project.org), which allowed averaging between leaves and comparison between treatments. At least 5 plants were measured per line/treatment combination.