Analysis of Germination Processes of Lettuce Seed by Means of Temperature and Anaerobiosis

Abstract

Although the seed of Grand Rapids lettuce has long been regarded as classical material for the study of photocontrolled germination (5,6,14,15), our knowledge of the nature and mechanism of its germin-ation is scanty (cf 11, 12, 32, 36). This condition is partly due to the complex nature of the processes, but is also in part due to the difficulty of separating the germination of the seed from the growtth of the embryo (22, 27). After the seed has been moistened with water, its photosensitivity increases sharply at first, reaches a maximum, then gradually decreases (6, 24, 26). The seeds photoinduced at the time of maximum sensitivity take at least 5 hours before visible protrusion of their radicles (22, 27), and 50 % of them have not protruded for about 9 hours. Thus the imbibition of water and the photoreaction are widely separated from any visible germination. Our studies suggest that the germination comprises 4 phases: A) preinduction phase, when the seed takes up water and prepares for induction by red light; B) induction phase, when red light brings about the maximum induction, and reversal by far-red is also maximal; C) postinduction phase, when the seecl undergoes a dark process; and D) phase of visible germination, when the radicle breaks through the surrounding coats. The existence of these 4 plhases becomes clear when an attempt is made to analyze the photoinduced germination processes per se as distinguished from the growtlh of the embryo (cf 12, 36). In a preliminary series of experiments it was found that germination did not take place under com-plete anaerobiosis, either in light or in darkness, but