Cell-Wall Histochemistry and Anatomy of Taro (Colocasia esculenta.)

Abstract

The cell-wall histochemistry and anatomy of the corm, petiole and leaf blade of taro [Colocasia esculenta (L.) Schott], an important South Pacific food plant, are described. The results are discussed in relation to the possible protective action of taro cell walls (dietary fibre) against a range of diseases, including colorectal cancer. Cell walls may protect against colorectal cancer by adsorbing carcinogens, and lignified, suberised, and possibly cutinised walls adsorb hydrophobic carcinogens more than walls lacking these substances. The only cells in taro with lignified walls are xylem tracheary elements. The corm is covered with a thick periderm, and the histochemistry of the walls of the phellem indicates the presence of suberin and associated waxes. The leaf blade and petiole are covered by a cuticle, and the presence of cutin and associated waxes is also shown histochemically. Parenchyma is the most abundant cell type with unlignified walls and occurs as aerenchyma in the cortex of the corm and in the petiole and midrib of the leaf blade. Mucilage ducts occur throughout the corm and their contents stain with a reagent (β-glucosyl Yariv reagent) specific for arabinogalactan-proteins (a soluble dietary fibre). Large numbers of starch granules occur in the cortex and central cylinder of the corm, but few occur in the leaf.