LOW-TEMPERATURE SCANNING ELECTRON-MICROSCOPIC OBSERVATIONS ON ENDOSPERM IN IMBIBED AND GERMINATED LETTUCE SEEDS

Lettuce (Lactuca sativa L.) seeds were observed using low-temperature scanning electron microscopy (LTSEM). The structure of imbibing and ge rminating seeds was characterized and compared with that of seeds in w hich these processes were inhibited by high temperature, far-red irrad iation, or polyethylene glycol. Germination is not associated with gen eral breakdown or digestion of the entire endosperm at the micropylar region. Embryos of seeds imbibed in polyethylene glycol, which inhibit ed germination, appeared to lack turgor and were not able to emerge fr om the endosperm. Thermal or far-red inhibitory treatments were associ ated with the appearance of complex membraneous structures in cells of the endosperm and the embryo.