Development of the recalcitrant (Homoiohydrous) seeds of Avicennia marina: anatomical, ultrastructural and biochemical events associated with development from histodifferentiation to maturation
1992
Farrant, J.M. | Pammenter, N.W. | Berjak, P.
Early histodifferentiation of the embryo of Avicennia marina (Forssk.) Vierh. was characterized by the formation of endosperm haustoria. Once the growth phase was initiated, subsequent embryo development was extra-ovular. The mature seed, therefore, was enclosed by a pericarp originating entirely from the ovary wall. Growth and reserve deposition was not initiated until 45-50 d after fruit set (DAFS), when respiratory activity had peaked. Water content remained constant from the earliest stages of embryogenesis to seed abscission and respiratory activity, although declining somewhat after the completion of histodifferentiation, remained relatively high throughout seed development. The ultrastructure of the meristematic root primordia was indicative of metabolic activity, remaining essentially similar in all respects from the end of histodifferentiation until the mature seeds were abscised. During this phase cotyledon cells became highly vacuolated and the soluble sugars, which constituted the major nutrient reserves of mature seeds, increased considerably. Seeds of A. marina initiate germination, without the requirement for additional water, as soon as they are shed. It is proposed that the accumulation of soluble sugars, rather than insoluble complex reserves, is a major factor in the developmental strategy of these highly recalcitrant seeds.
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