On the Development of Osteosclereids in Seed Coats of Pisum Sativum L.

The development of osteosclereids during seed-coat maturation in Pisum sativum was observed by light and electron microscopy. Osteosclereid precursors are small, densely staining cells which elongate and mature after the macrosclereids. The lateral cell walls in the region of the cell equator become heavily thickened preventing further expansion, while the ends of the cells retain their thin walls and continue to expand. This growth creates the bone-shaped cell typical of osteosclereids. The cells become separated from each other by accelerated circumferential expansion of the cell layers above and below them and by cell layers. Cell wall synthesis in osteosclereids involves coated and smooth vesicles from the Golgi, and vesicles with fibrillar contents from the endoplasmic reticulum.