Red-Light-Induced Endosperm Preparation for Radicle Protrusion of Lettuce Embryos

Light microscopic examination of red-light-treated Lactuca sativa achenes at various stages of imbibition revealed that, prior to visible germination (radicle protrusion), the endosperm cells of the micropylar end undergo rapid characteristic structural changes. The cytoplasm becomes highly vacuolated, and reserve materials are mobilized. Generally, these cells swell, while the cell walls remain PAS positive. In dark-, far-red, and red + far-red-light-treated achenes, however, the endosperm remains unchanged. The structural changes may be a prerequisite for endosperm rupture and radicle protrusion.