Changes in the Surface Appearance of the Endosperm During Lettuce Achene Germination

Abstract

The endosperm of lettuce achenes was observed with a scanning electron microscope (SEM). The surface of the endosperm of dry achenes and of 6-h imbibed achenes was smooth. Degradation of the endosperm in the micropylar region increased with time. Cracks and pits in the walls and surface of endosperm cells were evident, and the tip of the micropylar region of some achenes had a large break. The number of achenes with these openings increased to a peak after 12 h from the start of imbibition. The percentage of achenes with openings declined after 12 h because of germination. The percentage of germination after 24 h was the same as the percentage of achenes displaying endosperm degradation. Endosperm disruption was also determined in 12-h imbibed achenes in far-red light, darkness, and at temperatures of 24 or 35 C. Far-red light greatly inhibited both endosperm weakening (12 h) and germination (24 h); darkness was less effective. At 24 C, imbibition of achenes in darkness further decreased germination and endosperm weakening compared with light-treated achenes. Thermodormant achenes sown in darkness did not exhibit endosperm weakening, and thermodormant achenes sown in white light did. Light may play a role in endosperm weakening. Endosperm weakening after 12 h and germination after 24 h may be correlated.