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Structural changes during the in vitro germination of Vanilla planifolia (Orchidaceae)

Philip, V.J., Nainar, S.A.Z.
Annals of botany 1988 v.61 no.2 pp. 139-145
organogenesis, Vanilla planifolia, germination
A study is reported of histogenesis and organogenesis during the processes leading up to seedling formation in cultures of Vanilla planifolia. Prior to germination, all cells of the embryo increased in size rupturing the seed coat and initiating the protocorm stage. The cells of the protocorm were heavily laden with starch grains. Although all of the cells of the mature embryo were heavily laden with protein bodies, these were confined to the terminal cell descendents on emergence of the embryo from the seed coat, and they disappeared during differentiation of the meristem, indicating that some reserves were mobilized and utilized during germination. The terminal locus of embryonal axis did not differentiate into a cotyledon and epicotyl as in other angiosperm embryos but formed a thick meristematic layer. Bipolar differentiation within the meristem produced the shoot, and after a few leaves had been formed, the first root differentiated endogenously from the base of the meristem. Subsequent roots, however, appeared to originate more superficially. The chain of events appears to be quite unique to Vanilla amongst the angiosperms.