Medicinal Seeds: Pharmacognosy & Bioactive Principles

Learning Objectives

• The lecture aims to help students discuss pharmacognostical features of medicinal seeds, outline bioactive principles, discuss phytoconstituent detection procedures, and list therapeutic and toxic effects.

Seed Introduction

• A seed is defined as a mature fertilized ovule enclosing an embryo.
• The function of a seed is to ensure plant continuation and distribution.
• A seed’s main parts consist of the embryo, the endosperm, and the seed coat.

Ovule Structure

• A mature ovule consists of the stalk or funicle, and the body.
• The hilum is the point of funicle attachment to the ovule body.
• Sometimes the funicle extends to the base of the ovule to form a ridge, called the raphe.
• Chalaza is the site where vascular strands come from the funicle to the other parts of the seed and the location of the "mouth of the ovule".
• Micropyle is the point where the radicle of the seed germinates to give rise to the root.
• The embryo sac is the female gametophyte, located inside the ovule's nucellus.
• A mature embryo sac consists of three cells at each end, on either side of a centrally placed nucleus.
• The group of cells towards the micropylar end is called the egg apparatus.
• The central cell of the egg apparatus is the egg cell or ovum, which forms the female gamete.
• Synergids are the other two cells, one on each side of the egg cell, which are nonfunctional, short-lived, and disintegrate after fertilization.
• Antipodal cells are the group of three cells at the chalaza end, opposite to the egg apparatus; they have no definite function and disintegrate after fertilization.
• Definitive nucleus (secondary) nucleus is the large nucleus at the center of the embryo sac, which fuses with a male gamete to form the endosperm nucleus, which grows into the endosperm.

Ovule Forms

• Orthotropous ovules are straight, with the funicle, chalaza, and micropyle lying on one vertical line. Examples include Rumex and Piper.
• Anatropous ovules are inverted, the ovule body bends back alongside the funicle, and the micropyle lies close to the hilum
• Amphitropous ovules are transverse when the ovule body lies transversely at a right angle to the funicle, found in citrus.
• Campylotropous ovules are curved, with the ovule body curved like a horseshoe so that the micropyle and chalaza lie at one pole; the funicle does not fuse with the integuments, found in Brassica and Mirabilis.

Seed Structure

• The kernel consists of all tissue enclosed by the testa.
• The testa, or seed coat, develops from the integuments of the ovule
• Arillus/aril is an expansion extending from the funicle/placenta over the seed surface, like a bag that partly covers the seed, such as in cardamom.
• Arillode is an expansion extending from the micropyle over the seed surface, can be partly or completely cover the seed, such as in nutmeg.
• Caruncle is protuberance tissue arising from the testa near the micropyle, covers the area which is a localized fleshy outgrowth, example castor seed.
• Strophiole is protuberance originating from the hilum, like a crest, example colchicum and gram seeds.
• Wing is when the extension of the testa itself will cause a membranous sheet, example Pinus.
• Plume is the extension of the testa as a tuft of hair found on seed either at the top (Apocynaceae) or at the base (Salix) or carried by a stalk (Awn) in Strophanthus.
• The embryo is developed from the fertilized ovum.
• The endosperm surrounds the embryo and is developed from the primary endosperm nucleus.
• The perisperm is formed from the nucellus.
• Endosperm and perisperm are considered reserve food materials, like starch granules, aleurone grains, and fixed oil.
• Exalbuminous seeds have a kernel consists of only an embryo, like mustard.
• Albuminous seeds has a kernel that consists of an embryo and is surrounded by endosperm (linseed, fenugreek, Nux vomica) or endosperm and perisperm (cardamom, nutmeg)

Embryo

• The embryo consists of the plumule (primary shoot), the radicle (primary root), cotyledons (one (monocotyledons) or two (dicotyledons), and the hypocotyledons (region between the base of the cotyledons and the top of the radical).
• Embryo forms: straight (linseed, Nux-vomica), coiled or curved (poppy seeds), or spiral (Stramonium).
• Radical is bent on itself and can be accumbent (radicle bent against the edges of the two straight cotyledons, e.g., fenugreek), incumbent (radicle bent against one of the straight cotyledons, e.g., cannabis), or orthoplocous (cotyledons in the accumbent embryos are folded to enclose the bent radicle, e.g., mustard)

Testa Histology

• The testa consists of some or all of the following layers: Epidermis, Sub-epidermal layer, Sclerenchyma layer, Pigment layer, and Nutritive layer.
• The epidermis may be palisade-like cells (radially elongated cells with thickened cellulosic walls and thick cuticle, e.g., fenugreek), lignified sclereids (pitted walls, thickened, lignified hairs, e.g., Nux Vomica), prosenchymatous cells (elongated fiber-like cells), or mucilaginous cells (lumen filled with mucilage, e.g., linseed and mustard).
• The sub-epidermal layer may be basket-like cells (fenugreek), very large parenchymatous cells (mustard seed), or collenchyma (linseed).
• The sclerenchymatous layer, may be formed of one of multiple layers, that is, developed in any part of the testa. The sclerenchymatous layer can be the outer epidermis of the Testa (Nux vomica and Strophanthus) or the inner epidermis of the inner coat (linseed or cardamom).
• The pigment layer is responsible for the color of the seeds. It may constitute the outer or inner epidermis, or any other layer of the testa.
• The nutritive layer, originally formed of thin-walled parenchyma filled with starch, provides materials for the seed during ripening.
• The most important reserve food materials in seeds are starch, protein, fixed oil, and fat.

Semen Trigonellae

• Botanical origin: Dried seeds of Trigonella foenum-graecum L., belonging to the Fabaceae family.
• Description: Known as very hard seeds with a strong characteristic door. Seeds are irregularly rhomboidal, oblong, or square in outline, somewhat flattened and divided into 2 unequal parts by a groove in widest surfaces.
• Main active constituents: consist of Pyridine-type alkaloid, Steroidal sapogenin, non-essential amino acid, fixed oil (5-10%), and Mucilage 24%
• Uses and therapeutic use: Aids in lactation, improves insulin and weight loss. Can also raise testosterone, antioxidant, anti-inflammatory, and commercial steroid, such as contraceptive, synthesis

Semen Psyllii

• Botanical origin: The dried ripe seeds of Plantago afra (P. psyllium), P. indica (P.arenaria) and P. ovata, belonging to the Plantaginaceae family
• Common names are Planatgo seeds and Flea seeds
• Active ingredients: all seeds contain mucilage in the epidermis of the testa the volume is measured. On hydrolysis fraction causes yield d-xylose, l-arabinose and aldobiuronic acid, has fixed oil, and aucubin glycoside
• Uses: Plantago seeds are demulcents and treat chronic constipation, help with weight loss, ispaghula husk is used for purpose but has swelling factor, bulk forming laxative, treat high cholesterol, and an ingredient in manufactured breakfast cereals
• Psyllium side effects can include bowel obstructions, gases and stomach bloating, and choking.

Semen Lini

• Botanical origin is from the dried ripe seed of Linum usitatissimum L., and Family Linaceae.
• Macroscopical characters: The ovate seeds which are flattened, colored brown, glossy and pitted. Odorless although tasting oily and mucilaginous a transverse cut shows two large planoconvex cotyledons
• Constituents: fixed oil, mucilage, proteins
• Linseed oil: Extraction is done mechanically via a mill and will product a by product that is cake, a yellowish-brown drying oil.
• If exposed to air it may thicken gradually.
• Fats in linseed include: unsaturated fatty acid and saturated acids
• Uses include: Linseed poultice is used to make demulcent preparations, hydrolyzed linseed oil has usefulantibacterial properties, linseed is a valuable cattle food (aides in cardio protection), and reduces risk, blood sugar levels and atherosclerosis.