Imaging and Measurement of Meristems

To observe ASP1-GFP fluorescence, shoot apices of transgenic plants (T0 generation) were embedded in 5% (w/v) agar and sliced into 30-µm sections using a vibratome. GFP fluorescence was observed with a confocal microscope (LSM510, Zeiss).

Inflorescence meristems were observed by scanning electron microscopy as described by Tanaka et al. (2015). A top view of the oval-shaped inflorescence meristem was used for measurement of the major and minor axes by ImageJ (https://imagej.nih.gov/ij/). To measure SAM size, shoot apices of 8-week-old plants were dissected and fixed in acetic alcohol (1:3). After treatment with a clearing agent (16 g of chloral hydrate dissolved in 8 mL of 25% [v/v] glycerol), the samples were observed under DIC optics. The SAM size was measured just above the P1 primordium by using ImageJ.