Spherical organelles, analogous to seed protein bodies, fluctuate seasonally in parenchymatous cells of hardwoods

Abstract

A light microscopic study of the inner bark tissues of 11 temperate hardwoods showed seasonal differences in the degree of vacuolization and in the type and amount of storage material within phloem parenchyma and vascular cambium cells. Throughout the summer these cells were highly vacuolated, and starch-containing plastids were often present. During the overwintering period the typical large, central vacuoles were replaced by small, spherical organelles approximately 0.5–7.0 μm in diameter. The contents of the spherical organelles stained positively for protein. These organelles are considered to be analogous to protein bodies of seeds and to play a role in the storage of nitrogen. This study confirms and extends previous reports of protein bodies within parenchymatous cells of overwintering temperate trees. It further demonstrates that the organelles occur seasonally and that the formation of protein bodies for overwintering storage is a common phenomenon.