Ultrastructure of the epidermis and stomatal complex of balsam fir (Abies balsamea)

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Abstract
The ultrastructure of the epidermis and stomatal complex of A. balsamea (balsam fir) was examined. Needles were fixed at the time of emergence from the bud and at intervals thereafter. Epidermal cells in the youngest needles examined had a prominent nucleus with several nucleoli, ribosome-rich cytoplasm, a few rudimentary chloroplasts and small vesicles with osmiophilic material. With maturation, the vacuole expanded to nearly fill the cell leaving only a thin layer of cytoplasm around the wall. The walls underwent a high degree of thickening, and a wax and cuticle layer developed. Guard cells were located below the needle surface with specialized subsidiary cells overarching them and creating a stomatal antechamber. This cavity contained wax formations deposited even before the needles emerged from the bud scales. Guard cells were substantially matured at the time of bud break with a characteristic pattern of wall structure. Chloroplasts, which developed multiple starch grains, were abundant near the polar ends of the cells. Radial micellation of the walls was pronounced. Specialized hinge areas were noted. A region on the ventral wall, facing the pore, lacked lignification and showed distinct bends in the fibrillar material, which may be associated with opening and closing the stomate.

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