Lecture 1 Seeds, Pharmacognosy 2 (PG121) PDF

AMGAD MANSOUR, PhD Professor of Pharmacognosy  SEEDS What is seed? It is an integumented ‫ ﻣﺣﺎﻁﺔ ﺑﻐﻼﻑ‬fertilized ovule, specialized for the distribution, and continuation of the plant.  Structure of ovule A typical mature ovule consists of a mass of parenchymatous tissue,...

AMGAD MANSOUR, PhD Professor of Pharmacognosy  SEEDS What is seed? It is an integumented ‫ ﻣﺣﺎﻁﺔ ﺑﻐﻼﻑ‬fertilized ovule, specialized for the distribution, and continuation of the plant.  Structure of ovule A typical mature ovule consists of a mass of parenchymatous tissue, called nucellus which is with the exception of a narrow opening called micropyle; enveloped by two integuments.  The basal part of the nucellus, from which arise the integuments is somewhat swollen and called chalaza. The ovule may be attached at the chalaza to the placenta by small stalk, called funicle; Funicle may fuse for some distance with the integument to form raphe. Through the funicle runs the vascular bundles from the placenta to the base of the nucellus and terminates commonly in the chalaza. Types of ovules 1- Anatropous It is the most common type of ovules. Raphe is formed and extending the whole length of the seed e.g. Linseed and Almond 2-Atropous or orthotropous If the growth of the ovule is uniform, it is straight, not curved 3- Amphitropous The ovule is rotated on its stalk through an angle of 90º instead of 180º. There is short raphe runs from the Chalaza to the half the distance to the Micropyle. Short Raphe 4-Campylotropous It is characterized by a rapid growth of one side of the nucellus and the development on the other side almost arrested.  Structure of the Seed Seed consists of 3 parts (1) Seed coat (Testa) (2) Reserved food tissues (endosperm, perisperm) (3) Embryo (composed of 1-2 cotyledons)  Seed coat 2 integuments (testa) Remains of nucellus perisperm Fusion of polar nuclei Endosperm Fertillization of egg cell by pollen grains Embryo  Outgrowths of Testa 1-Arillus or Aril: 2-Arillode: arising from the 3-Caruncle: arising from Hilum Cardamom‫ﺍﻟﺣﺑﻬﺎﻥ‬ arising from micropyle micropyle ‫ﺟﻭﺯﺓ ﺍﻟﻁﻳﺏ‬e.g. nutmeg ‫ﺍﻟﺧﺭﻭﻉ‬as in Ricinus 4-Strophiole: 6-Plume: it is an extension arising along the 5-Wing: in the form of hairs at the line of raphe, It is an extension apex or the base of the seed. as in Colchicum. of the test It may be sessile or carried as in on stalk as in Strophanthus Strophanthus seed. and thus called awn.  Storage of Food in Seeds All seeds contain reserve foods for the nourishment of the embryo during germination. This may be present in the endosperm, or perisperm or both in case of albuminous seeds. The reserve food materials are two types viz. Carbohydrates (as starch) which supply C, H & O and fixed oil as well as proteins (as aleurone grains) which supply N, S & P. Albuminous: endosperm and perisperm developed and surrounded by integument e.g. linseed. Exalbuminous: free from endosperm and perisperm, food stored in cotyledons in embryo e.g. black mustard. N.B. Perisperm is remnants of nucellus. Endosperm is developed from the fusion of two polar nuclei in the embryo sac.  Forms of Embryo a)Accumbent The radicle is bent against the two flat cots as Foenugreek seed 1-Straight embryo as in Strophanthus or 2-Curved embryo : as in Stramonium. Linseed. 3- Bent embryo b) Incumbent: the radicle is bent against the flat surface of the one of the 2 cots as in Cannabis seed c) Orthopolocus: it is an incumbent in which the 2 cots are bent to include the radicle in between as in Mustard seeds. Seed coats may show the following structure 1- Epidermis 2- Hypodermis 3- Sclerenchymatous Layer 4- Nutrient Layer 5- Pigment Layer Foenugreek seed colocynth Nux-vomica Beaker shaped hypodermis Sclerenchymatous Palisade epidermis Epidermis Collenchymatous Parenchymatous layer layer of hypodermis of hypodermis Linseed Linseed Cardamom seed Parenchymatous Prosenchymatous epidermis epidermis 2- Hypodermis, it may be: a- Parenchymatous formed 1, 2 or 3 layer as in Cardamom seed. b- Collenchymatous formed of 1 or 2 layers as in Linseed. c- Large parenchymatous cells called giant cells as in Black Mustard. d- Beaker shaped cells with narrow apex and wide base, e.g. hypodermis of the Foenugreek seed. 3- Sclerendymatous Layer: In Nux vomica and Strophanthus, the epidermis is Sclerendymatous so the protective function of the testa was carried out by the epidermis and so the seed coat is formed of one integument. But when the epidermis of the seeds is parenchymatous or prosenchymatous, the seed coat is usually formed of two coats and showing a sclerenchymatous layer. The black Mustard & linseed and cardamom seed have sclerenchmatous layer. In colocynth seed, the entire testa consists of many layers of thickened cells. Linseed black Mustard In colocynth seed, the entire testa consists of many layers of thickened cells. cardamom seed 4- Nutrient Layer It is consisted of several layers of thin walled parenchyma. The cells of which are filled with starch granules. 5- Pigment Layer In all colored seeds, pigment is deposited in one layer of the testa e.g. linseed and black mustard seed. 6- Kernel is the seed without testa or it may consist of embryo with endosperm and perisprem as in nutmeg. a- Perisperm: When it is present, it is usually composed of thin walled parenchyma containing abundant starch granules as in Cardamom. b- Endosperm: It is composed of cellulosic walled parenchyma containing reserve food materials. The walls are thin, but in some seeds as Nux vomica, the walls become very thick and composed of hemicellulose. c- Cotyledons: It is formed from thin cellulsoic parenchymatous cells containing reserve food materials, like starch, fixed oil and aleurone grains.