Seed structures, fertilization and examples

• The lecture covers introductory information about seeds, including definitions, structures, markings, types, classifications, and examples of medicinal seeds containing cardiac glycosides and alkaloids.

Seed Basics

• A seed is a mature, fertilized, and enlarged ovule.
• Seeds facilitate transportation and ensure the continuation and distribution of plants.
• A fruit is a mature, fertilized ovary containing the seeds.
• Seeds are surrounded by the ovary wall, also known as the pericarp.

Ovule Structure

• The ovule consists of the pericarp, integuments (future testa), ovary wall, nucellus, megasporocyte and endosperm, funicule (future hilum) and chalaza.
• The megasporocyte creates what differentiates into a zygote

Fertilization Effects

• After fertilization, the ovule becomes a seed.
• Integuments or coats become the seed coat.
• The nucellus becomes the perisperm.
• The embryo sac or megaspore becomes the zygote and primary endospermic nucleus.
• The zygote then becomes the embryo (cotyledons + radicle + plumule).
• The primary endospermic nucleus becomes the endosperm.

Surface Markings on the Testa

• Hilum: A scar left after the funicle (stalk) is removed from the seed.
• Micropyle: A minute hole at the top of the seed that allows water transport during seed germination.
• Chalaza: Position at the base of the nucellus where the vascular strand of the stalk branches.
• Raphe: Vascular strand in anatropous and amphitropous seeds located where the stalk.

Ovule Types

• Atropous (Orthotropous): The ovule is erect, with the funicle, nucellus, and micropyle on a straight line; there is no raphe.
• Anatropous: The stalk grows rapidly, adhering to one side causing the ovule to invert 180°.
• The micropyle comes close to the hilum with the chalaza at the opposite end.
• The raphe extends along the ovule's length.
• Amphitropous: The stalk adheres to the ovule, rotating it 90°.
• The hilum, chalaza, and micropyle are widely separated, with the raphe running only from the hilum to the chalaza.
• Campylotropous: The nucellus and coats develop rapidly while the other side is arrested. The hilum, chalaza, and micropyle are together at one end, and there is no raphe.

Kernel Composition

• The kernel includes all structures of the seed enclosed in the testa.
• The kernel may be composed of the embryo alone, such as in beans.
• The kernel may be composed of the embryo and endosperm, such as in linseed.
• The kernel may be composed of the embryo, endosperm, and perisperm, such as in cardamom.

Seed Types

• Exalbuminous (Non-Endospermic) Seeds: The embryo is surrounded by the testa, and the nucellus and embryo sac are absorbed, e.g., beans
• Albuminous (Endospermic) Seeds: The seed is composed of the embryo and endosperm surrounded by the testa; linseed.
• The perisperm, derived from the nucellus, surrounds the endosperm and embryo, e.g., cardamom.

Embryo Types

• Straight
• Curved
• Coiled
• Bent on Itself:
  • Incumbent: The embryo is bent, and the radicle is against the cotyledons (e.g., cannabis).
    • Accumbent: The embryo is bent so the radicle is against two cotyledons (e.g., foenugreek).
  • Orthoplocous: The cotyledons fold along the midrib, enclosing the bent radicle against the cotyledons (e.g., mustard).

Outgrowth Types

• Arillus: Arising from the funicle or hilum being dry and membranous (e.g., cardamom).
• Arillode: Arising from the micropyle and being fleshy.
• The outgrowth in Nutmeg, Mace arises from both the funicle and micropyle.
• Considered as arillus or arillode
• Caruncle: Arises from the micropyle and is localized and fleshy (e.g., castor seed).
• Strophiole: Barrel or wing-shaped enlargement along the raphe (due to increased parenchyma; e.g., Colchicum).
  • Wing: Extension of the testa that is membranous (e.g., Pinus).
• Plume or Tuft of Hairs:
  • Sessile: Arising from the base or apex of seeds (e.g., Argel and Salix).
  • Stalked: Arises at the apex of the seed/Awn (e.g., Strophanthus).

Reserve Food Material

• Seeds contain carbohydrates like starch, cellulose, sugars, and hemicellulose.
• Seeds contain fixed oils and proteins found in aleurone grains.
• Aleurone grain (protein body), is a specialized dry vacuole where storage proteins accumulate in a stable form.
• The cells containing aleurones form the aleurone layer. -Aleurone grains are important in the differentiation between different seeds and other plant organs.

Types of Aleurone Grains

• Simple (e.g., cereals)
• Globoids (e.g., plantago)
• Globoid and Crystalloid (e.g., castor seeds)

Seed Classification by Reserve Material

• Starchy seeds (e.g., wheat)
• Oily seeds (e.g., castor)
• Hemicellulosic (horny) seeds (e.g., Nux vomica)
• Mucilaginous seeds (e.g., psyllium)
• Proteinous seeds (e.g., Vicia faba)

Seed Histology

• Seed Coat:

• Epidermis including palisade-like layer (e.g., leguminous seeds).

• Sclerids (e.g., Nux vomica).

• Mucilaginous layer (e.g., linseed and mustard).

• Prosenchyma (e.g., cardamom).

• Sclerenchyma layer

• Pigment layer

• Nutrient layer

• Perisperm and endosperm

• Embryo

Medicinal Seeds and Active Constituents

• Seeds containing cardiac glycosides, e.g., Strophanthus
• Seeds containing alkaloids, e.g., Nux vomica and Colchicum
• Seeds containing mucilage, e.g., linseed and fenugreek
• Seeds containing volatile oil, e.g., cardamom and nutmeg
• Seeds containing derived volatile oil, e.g., black mustard
• Seeds containing fixed oil, e.g., almond seed and castor seed

Seeds Containing Cardiac Glycosides

• Cardiac glycosides are composed of aglycone and a sugar part.
  • Aglycone = steroidal nucleus + lactone ring.
• The lactone ring is either 5-membered (cardenolide) or 6-membered (bufadienolide). -Sugar part may contain deoxy sugar, like cymarose or digitoxose

Semen Strophanthi (Seeds Containing Cardiac Glycosides)

• It is also known as Strophanthus Seed, Arrow poison seed.
• Origin: Dried ripe seeds of Strophanthus kombe, S. hispidus, & S. gratus deprived of their awn; Fam. Apocynaceae.
• Geographical Source: Indigenous to East Africa
• Shape: Flattened, lanceolate to ovate lanceolate Oule type: Anatropous
• Seed type: Albuminous
• Embryo type: Straight

Strophanthus kombe Characteristics

• Odor: Slight unpleasant odor
• Taste: Bitter

Strophanthus kombe Powder Characteristics

• Color: Greenish-brown to brown
• Odor: Unpleasant
• Taste: Bitter

Active Constituents of Strophanthus kombe

• Cardiac glycosides occur in 1.8-10% amounts; including K-strophanthin (or K-strophanthoside), which is a mixture of cymarin, K-strophanthoside B, K- strophanthoside A, and cymarol.
• 30% Fixed oils
• Alkaloids: choline and trigonelline.
• Resin

Chemical Tests For Cardiac Glycosides

• Prepare chloroform-based extract of the powder.
• Keller-Killani test used for 2-deoxy sugar
• Kedde’s test: Used for 5-membered lactone ring
• Baljet’s test: Also used for the 5-membered lactone ring
• Libermann-Burchard’s test for steroidal nucleus

Chemical Reactions indicating Cardiac Glycosides

• Keller Killiani Test: Acetic acid and ferric, creates a brown layer at the junction and upper layer appearing bluish green
• Kedde's Test: A violet color results from reacting with Dinitrobenzoic acid
• Baljet's Test: With picric acid, an orange red color indicates a positive result.
• Libermann-Burchard's Test: A reddish violet color at the junction that acquires a green color with acetic anhydride

Identity

• When the section of seeds is treated with sulphuric (80%), the endosperm acquires an emerald green color while the embryo acquires a green color

Action and Uses of Cardiac Glycosides

• It is a cardiac stimulant and cardiotonic. Cardiac stimulant & cardiotonic properties.
• Improves action for those with congestive heart failure {digitalis}.
• Mild diuretic that improves blood flow.
• Less cumulative and less gastrointestinal irritant versus digitalis.

Seeds Containing Alkaloids

• Nux Vomica
• Colchicum
• Stramonium

Semen Strychnii (Nux Vomica)

• Also referred to as Nux vomica
• Seed source: Strychnos nux-vomica (Fam. Loganiaceae) dried ripe seeds.
• Ceylon, India, and Siam forests are indigenous areas
• Type of Seed: Very hard, horny, and albuminous
• Outgrowth: Absent
• Ovule: Atropous type
• Embryo: Straight

Active Constituents of Semen Strychnii

• 2.5 % Alkaloids, mainly strychnine and brucine
• Glycosides (loganin, intermediate alkaloid).
• Fixed oil

Chemical test indication

• When mixed with Mandelins reagent produced a violet color, most prominently innermost
• Nitric acid produces a orange red color, most prominently outermost

Uses

• Increases blood pressure
• May be used as a respiratory stimulant during cases of poisoning
• Folk medicine has employed it as a bitter tonic and stomachic.
• Improves appetite and digestion (folk medicine)
• Treat constipation (small doses)

Toxicity

• Death by asphyxia due to convulsions of the respiratory muscles
• Toxic and induces convulsions in large doses.

Semen Strychnii (Nux Vomica) Macroscopical Characters

• Shape: Disc or compressed button, covered in short hairs, satiny
• Ridge: Raised ridge from the micropyle
• Odor: Odorless
• Taste: Bitter

Semen Strychnii (Nux Vomica) Transverse Section

• Epidermal cells with trichomes (10 lignified ribs each)
• Hyaline layer
• Hemicellulosic endosperm (plasmodesmata, fixed oil, aleurone grains)

Semen Colchici

• Dried ripe seed of Colchicum autumnale Fam. Liliaceae.
• Alkaloids (0.5 - 0.8%) colchicine
• Resin
• Fixed oil

Chemical test indication

• When mixed with Conc. HCL it prodcued a Yellow endosprem

Side effects

• Teratogenic damage.
• Kidney & liver damage
• Loss of Hair
• Bone damage marrow

Semen Colchici (Cont.)

• Treats relieve pain and inflammation of Gout , and Mediterranean conditions
• Plant hormone in used for polyploidy
• Prevent cell division when using for caner