Structural Aspects of Protein Accumulation in Developing Pea Cotyledons. II. Three-Dimensional Reconstructions of Vacuoles and Protein Bodies From Serial Sections

Abstract

The three-dimensional structure of vacuoles and protein bodies seen in developing cotyledons from pea (Pisum sativum L.) have been reconstructed from serial sections. At days 12 and 15 after flowering, serial sections 1 µm thick of epoxy-embedded seed tissue were used to determine vacuole morphology while, at day 20, serial sections 0.25 µm thick were examined by electron microscopy to ascertain protein body morphology. At day 12 there are one or two large vacuoles having extremely complex protrusions emanating from a larger central vacuolar volume. This gives rise to up to 20 apparently discrete vacuole profiles in a given section through a cell. By day 15, there are many smaller, approximately spherical, vacuoles and also some that are more complex. At day 20 most protein bodies are discrete, spherical structures, although a few irregularly shaped bodies are seen. The results support the concept of a large highly convoluted central vacuole fragmenting to give rise to the protein bodies seen towards seed maturity.