Days

Figure 2.10 Changes in fresh and dry weight in megagametophyte, seedling, and total of both seeds and embryo of ponderosa pine seedlings during stratification and germination. From Ching and Ching (1972).

Compositional changes of Douglas fir seeds during germination are shown in Fig. 2.12. Lipids, the major food reserves, originally made up 48 and 55% of the dry weight of the gametophyte and embryo, respectively.

Figure 2.11 Starch distribution in cotyledons of black oak acorns: (A) cells of dormant acorns, (B) cells of stratified acorns, and (C) cells of germinated acorns. From Vozzo and Young (1975), Bot. Gaz., © University of Chicago Press.

Figure 2.12 (A-R) Changes in weight and composition of embryo, megagametophyte, and whole seed of Douglas fir during germination. D, Air-dried seed; S, stratified seed. From Ching (1966).

Figure 2.12 (A-R) Changes in weight and composition of embryo, megagametophyte, and whole seed of Douglas fir during germination. D, Air-dried seed; S, stratified seed. From Ching (1966).

During early germination, the lipids in the gametophyte decreased greatly and were used for embryo development. The dry weight of the embryo increased by 600%, and that of the megagametophyte decreased by 70%.

In oily seeds a concomitant increase in activities of lipase, isocitrate lyase, and fructose 1,6-biphosphatase indicates metabolism of stored lipids by gluconeogenesis. In hazel seeds held at 20°C, total lipase and isocitrate lyase activities were low. In seeds stratified at 5°C, total lipase and isocitrate lyase activity increased greatly in both the embryonic axis and cotyledons

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