Vitrified plants : towards an understanding of their nature

Submerged aquatic plants and plants in tissue culture both grow in an environment that does not allow transpirational pull to be exerted on plant organs. The tissue culture environment sometimes induces abnormal growth, a phenomenon known as vitrification or hyperhydricity. The hypothesis that a water-saturated environment induces vitrification by altering the structure of plants in vitro is explored by comparing characteristics of submerged aquatic and vitrified plants. Structural similarities include limited vascular development, reduced lignification of xylem cell walls, a thinner cuticle, absence of palisade tissue in leaves, abnormal stomata and large intercellular spaces in the leaves. However, a major difference is that in aquatic plants the intercellular spaces are air filled whereas those of vitrified leaves are, at least, partially filled with water. It is speculated that lack of water movement through plants grown in water-saturated environment influences xylem development and for plants grown in vitro it may contribute to the filling of the intercellular spaces. The comparison between submerged aquatic plants and vitrified plants suggests that vitrification is primarily a plastic response of plants to the in vitro environment and can only be remedied by altering the environment, particularly the humidity.