Histological and ultrastructural changes in canola (Brassica napus) funicular anatomy during the seed lifecycle

Abstract

We examined the dynamic cellular changes that occur in Brassica napus L. funiculus histology and ultrastructure over developmental time by using light and transmission electron microscopy. Over the course of development, the funiculus significantly increased in size. This was a result of increased cell numbers as well as the deposition of additional wall material in the epidermis and vasculature layers of the funiculus. Conversely, the intermediate cortex layer broke down, detached from adjacent tissues, and developed large intercellular spaces. There was a loss of cytoplasm in the epidermis although this tissue remained intact. This cellular degeneration was correlated with a reduction in starch and other changes in organelle features. A pronounced increase in the number of vascular elements, both in the xylem and phloem tissues, also occurred as the funiculus matured. We present the first detailed histological examination of the funiculus in B. napus, one of the most economically important crops in Canada, and discuss the importance of cellular changes required for development as they relate to the three primary tissue systems of the plant.