Morphology of secretory structures and essential oil composition in Mentha cervina L. from Portugal

ABSTRACT: Mentha cervina L. is an aromatic plant that is traditionally used in the Alentejo region of Portugal to flavour food dishes and for the medicinal properties of the essential oil produced in its glandular trichomes. The morphology and distribution of the secretory structures of 20 populations was studied by light and scanning electron microscopy and revealed a great similarity in the type and distribution of glandular and non-glandular trichomes. In addition, two populations were surveyed at different stages of their life cycles. This showed that both maximum trichome density and maximum filling capacity of the glandular trichomes are attained early on. The GC and GC–MS chemical analyses showed that pulegone (62–80%), isomenthone (3–18%) and limonene (3–7%) are the main components of M. cervina essential oils. Cluster analysis of the identified essential oil components revealed a major chemical consistency between the 20 populations evaluate

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\ub74 and reacted positively with Alcian blue pH 2\ub75, 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

Seed Coat Structure and Histochemistry of Abelmoschus esculentus. Chalazal Region and Water Entry

The seed coat structure and histochemistry of Abelmoschus esculentus were studied by bright-field, fluorescence and scanning electron microscopy. The seed coat was typical of species of the Malvaceae. The endotesta cells had inner tangential walls which were very thick and autofluorescent. The occurrence of phenolic substances at this level has been related to seed coat imposed dormancy. The palisade cells were composed of three differently shaped parts: an upper \u2018prismatic part\u2019, a medium \u2018transition part\u2019 and a lower \u2018twisted part\u2019. The former was rich in hydrophilic substances, the latter was lignified. The swelling of the \u2018prismatic parts\u2019 was related to seed coat cracks. The region controlling onset of water entry was thought to be the chalazal area. Thanks to the presence of a large amount of highly acidic polysaccharide, water was able to penetrate from the permeable maternal tissue, through the chalazal cap and plug as far as the boundary between the palisade and underlying mesophyll. During imbibition of water a kidney-shaped \u2018blister\u2019 was seen to rise, formed by separation of the palisade cells from an underlying single layer of subpalisade cells. The palisade layer forming the blister roof showed the same histochemical characteristic of other seed regions. The single layer of the blister floor showed an affinity with Toluidine Blue O and Alcian blue. Both blister roof and floor were strongly autofluorescent