Testa structure and Histochemistry Related to Water Uptake in Leucaena leucocephala Lam. (De Wit)

The testa structure and histochemistry of Leucaena leucocephala Lam. (De Wit) seed were investigated by bright-field and fluorescence light microscopy, and scanning electron microscopy. The testa consisted of several separate layers. Externally there was a non-cellular layer made up of two parts differing in histochemical characteristics: an "outer strip" rich in hydrophilic substances, and a "thicker part" showing the occurrence of phenolics, involved in water impermeability control. A second underlying thin layer was formed by the palisade cell caps, joined one to another. This layer, which we called the "cap film ", became metachromatic reddish-blue with Toluidine O pH 4·4 and reacted positively with Alcian blue pH 2·5, revealing the presence of polysaccharide hydrophilic material. The palisade cells consisted of two parts, having different structures and histochemical features. The furrowed upper part revealed the simultaneous presence of hydrophilic and hydrophobic substances in the furrows and in the ribs respectively. The corresponding periclinal section showed a central daisy-like pattern (made up of hydrophilic material) with a small chain of tiny spots (made up of hydrophobic material) all around it. The inner part of the palisade cells was also furrowed, but showed only hydrophobic substances of lipidic nature, detected by Auramine O and Phosphine 3R. The light line was found to be rich in callose as shown by the strong fluorescence induced by Aniline Blue. These findings add supporting evidence of the complex structure and composition of the Leucaena leucocephala testa.