Autecological studies on Audouinia capitata (Bruniaceae). 7. Nutritional aspects in the mature seed

Lipids and proteins are the major storage compounds present in the starchless endosperm of dormant A. capitata seed. Calcium oxalate crystals are present in protein bodies of the epidermal endosperm, and in the pericarp cells. The globoid inclusions of protein bodies are a major source of P, K, Cl and Mg and the epidermal endosperm crystals, a major source for Ca. No crystalloids are found in the protein bodies. The seeds store N and P. They also contain substantial concentrations of Cu, Zn and Mn. Lower amounts of these elements are present in the pericarp. Nutrients in the pericarp of the indehiscent fruit are probably utilized by the developing seedling. The high N, P and lipid content in the seed, and also the distribution pattern of calcium oxalate crystals in the seed and pericarp, seem to be beneficial evolutionary adaptations. Lipids in seeds from the soil seed bank differ quantitatively from those in fresh seeds. Low densities of protein bodies are found in many seeds resulting in deficiencies of proteins and mineral elements. This may partially explain high incidence of pre-emergent seedling mortality contributing to the rarity of the species. Lipiede en proteïene is die hoofreserwes in die stylselvrye endosperm van rustende saad van A. capitata. Kalsiumoksalaatkristalle kom in die proteïenliggaampies van die buitenste endospermlaag en in die perikarp voor. Die globoïedinsluitsels is ’n hoofbron van P, K, Cl en Mg, en die kristalle van die buitenste endospermlaag, ’n hoofbron van Ca. Kristalloïede word nie in die proteïenliggaampies aangetref nie. Die sade stoor N en P. Dit bevat ook aansienlike hoeveelhede Cu, Zn en Mn. Laer hoeveelhede van hierdie elemente kom in die perikarp voor. Voedingstowwe in die perikarp van die nie-oopspringende vrug word waarskynlik deur die ontwikkelende saailing benut. Die hoë N-, P- en lipiedinhoud in die saad, sowel as die verspreidingspatroon van kalsiumoksalaatkristalle in die saad en perikarp, is blykbaar voordelige evolusionêre aanpassings. Lipiede in sade van die grondsaadbank verskil kwantitatief van dié in vars sade. Lae digthede van proteïenliggaampies in baie sade gee aanleiding tot tekorte in proteïene en minerale elemente, wat belangrike faktore in die hoë voorkoms van vooropkoms-saailingmortaliteit mag wees en tot die skaarsheid van die spesie mag bydra.