Structural Changes During the in vitro Germination of Vanilla planifolia (Orchidaceae)

A study is reported of histogenesis and organogenesis duringthe processes leading up to seedling formation in cultures ofVanilla planifolia. Prior to germination, all cells of the embryoincreased in size rupturing the seed coat and initiating theprotocorm stage. The cells of the protocorm were heavily ladenwith starch grains. Although all of the cells of the matureembryo were heavily laden with protein bodies, these were confinedto the terminal cell descendents on emergence of the embryofrom the seed coat, and they disappeared during differentiationof the meristem, indicating that some reserves were mobilizedand utilized during germination. The terminal locus of embryonal axis did not differentiate intoa cotyledon and epicotyl as in other angiosperm embryos butformed a thick meristematic layer. Bipolar differentiation withinthe meristem produced the shoot, and after a few leaves hadbeen formed, the first root differentiated endogenously fromthe base of the meristem. Subsequent roots, however, appearedto originate more superficially. The chain of events appearsto be quite unique to Vanilla amongst the angiosperms. Vanilla planifolia, protocorm, starch grains, protein bodies