Fluctuation of Vegetative Storage Proteins in the Seedlings of Swietenia macrophylla, Analogous to the Seasonal Changes of Those in the Shoot of the Adult Tree

In order to identify appropriate plant materials for studying the gene expression and biological function of vegetative storage proteins (VSPs) in woody plants, the VSPs in the seedlings of Swietenia macrophylla King were investigated by using light microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)and Western-blotting. The seed of S. macrophylla was rich in storage proteins that accumulated in the vacuoles of cotyledon parenchyma cells in appearance of compact spherical grains. The growth and development of S.macrophylla seedlings were characterized by an obvious growth rhythm. The storage proteins in seeds disappeared during seedling growth while VSPs appeared in the stem 2 weeks after seedling leaves matured. Thereafter,the VSPs in the seedling stem almost exhausted during new shoot growth, and when the leaves of new shoot just matured, both the stem beneath the new shoot of seedlings and the stem of new shoot started to accumulate VSPs. Nitrogen application dramatically increased the level of VSPs, but had little influence on the dynamics of VSP consumption and accumulation in seedling stem. Together with these data, the fluctuation of VSPs in seedlings was very similar to that in the branches of the adult trees. In addition, seedlings are easy to be treated due to their small size. Our results suggested that S. macrophylla seedlings were suitable for investigating the biological roles of VSPs and the mechanism of nitrogen storage in trees.