The micromorphological distribution of bound calcium in needles of Norway spruce [Picea abies (L.) Karst.]

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Abstract
The distribution of bound calcium in spruce needles is visualized by various microscopical techniques. Ca pectate occurs in the middle lamellae of cell walls and in a surprisingly great concentration in the thick cell walls of the sieve cells and transfusion parenchyma. The major fraction of the calcium, however, is bound in the form of insoluble Ca oxalate crystals, which occur extracellularly on the outside of the walls of mesophyll cells which face the intercellular spaces. Furthermore, numerous small crystals appear within the cell walls of the epidermal cells, especially in the cuticular layer. The development and distribution of these apoplastic crystals is described in detail. Some hypotheses are finally presented for possible interpretations of these unusual patterns of the crystallization of Ca oxalate outside the vacuole.