Structure and Ultrastructure of the Cotyledon of Date Palm (Phoenix dactylifera L.)

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Abstract
The cotyledon of the embryo of the date palm (P. dactylifera L.) is composed of 3 cell types with similar ultrastructure. These 3 types (the parenchyma, protoderm and procambium) can be distinguished on the basis of position, size and shape within the embryo. The procambial strands in the cotyledon consist of a ring of sympodia that diverged from the hypocotyl; each sympodium bifurcates 2-3 times to form 49 or more separate bundles at the distal end of the embryo, where they are situated very close to the cotyledon surface. Although the most prominent organelles are protein and lipid bodies, all cells also contain crystalline protein fibers and small electron-dense bodies bound in vacuoles. The amount of water in the fixative affected several structural features of the cells, primarily the appearance of the plasmalemma. From the rate of hydration and the amount of extractable water in the tissue, the most realistic primary fixation was obtained with 2% formaldehyde in 80% glycerol. This study provides a structural basis for studies of palm germination.