Inclusions in nuclei and plastids of Boraginaceae and their possible taxonomic significance

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Abstract
A survey of 68 species representing 28 genera in the family Boraginaceae was conducted at the ultrastructural level to determine presence of nuclear crystalloids in sieve elements and occurrence of crystalline structures in chloroplasts of phloem parenchyma cells. Nuclear crystalloids were identified in 55 of the species examined, and 25 of the species contained chloroplast crystals. The nuclear crystals were mainly composed of thin rods densely packed in parallel arrangement. Their sizes, shapes, and numbers varied, but they were basically prismatic or possibly cubical. During maturation, the sieve element nuclei disintegrated and the crystalloids were released into the cell lumen where they remained intact. Loosely arranged paracrystalline components associated with the dense nuclear crystalloids were found only in the genus Amsinckia. Crystalline inclusions in the parenchyma chloroplasts were made up of fibers loosely aligned in a herringbone pattern. The lability of the chloroplast crystals to the proteolytic enzyme, protease, was tested on 10 species, and only Onosma stellulatum Waldst. & Kit. chloroplast crystals were routinely digested. The high percentage of nuclear crystalloids found in this family suggests that these inclusions could be valuable as a systematic character. Key words: sieve elements, nuclear inclusions, plastid crystals, Boraginaceae.