On the ultrastructure of needles of Pinus silvestris L.
Walles, Björn; Nyman, Bengt; Aldén, Torsten
The ultrastructure of the different cell types in mature needles of pine (Pinus silvestris L.) is described. The epidermal cells are protoplasma-free with prominent secondary walls. The sunken guard cells have chloroplasts of a simple structure and many mitochondria. A hypodermal layer is formed by living vacuolated fiber cells. The mesophyll cells, which have tanniniferous vacuoles, are rich in chloroplasts and mitochondria and contain microbodies. The resin ducts have secretory cells with a unique kind of plastid, apparently engaged in resin production. The endodermal cells are characterized by strongly osmiophilic globules in the vacuoles. The transfusion tissue consists of thin-walled deformed tracheids with bordered pits and parenchyma cells with tanniniferous vacuoles of different types. Like endodermal cells these parenchyma cells have simple amoeboid chloroplasts. Albuminous cells with numerous small tannin-free vacuoles and localized wall thickenings traversed by bunches of plasmodesmata are found on the outer side of each bundle. The adaxial xylem contains protoxylem tracheids with spiral wall thickenings and metaxylem elements with evenly thickened walls. A fusiform cambium is inserted between the xylem and the phloem. The sieve cells have unique multilayered secondary walls. Plastids in these cells contain clusters of protein fibrils which become released into the protoplast.
ultrastructure; needles; conifers; Pinus silvestris
Studia Forestalia Suecica
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