Ultrastructural and chemical studies on seeds of Bulnesia schickendantzii and Bulnesia bonariensis

Bulnesia, a genus of the Zygophyllaceae, comprises two subgenera, subgenus Bulnesia and subgenus Gonopterodendron. One species of each subgenus was studied: B. schickendantzii and B. bonariensis, respectively. B. schickendantzii endosperm consists of four to six cell layers. Cell walls are composed of a middle lamella, a very thick outer wall and a thin inner wall. B. bonariensis endosperm is reduced to one layer of cells. The cell walls are formed by a middle lamella and a thinner wall. Protein bodies are observed in the embryo of both species and in the endosperm of B. schickendantzii. Lipid vesicles are present in the embryo and endosperm of both species. Phytin crystals, present in the protein bodies of B. schickendantzii, are rare in the protein bodies of B. bonariensis. B. schickendantzii endosperm contains the majority of sugars and proteins. In B. bonariensis the higher percentage of carbohydrate and protein is found in the embryo. Determination of neutral sugars was performed after acid hydrolysis. Sugars were analysed as alditol acetates by gas-liquid chromatography. Arabinose, xylose, galactose and glucose are the main monosaccharides but the ratio differs in tissues of both species. Soluble proteins were analysed by polyacrylamide gel electrophoresis, showing a different profile in tissues of both species. Very few bands are glycosylated. The ultrastructural and chemical differences observed between both species suggest the segregation of Gonopterodendron from the genus Bulnesia as a separate genus and encourage further studies of the other six species in order to confirm this assertion.