Seeds PDF - Fall 2023

PG303-PGC303 Seeds Dr. Samah Shabana Fall 2023  A seed is a fertilized ovule, which contains an embryo. It is a mature fertilized integumented ovule. Plant reproduction Fertilization of ovules by pollen grains Ovules are transformed to give...

PG303-PGC303 Seeds Dr. Samah Shabana Fall 2023  A seed is a fertilized ovule, which contains an embryo. It is a mature fertilized integumented ovule. Plant reproduction Fertilization of ovules by pollen grains Ovules are transformed to give seeds Ovary swells and enlarge to give the fruit (enclosing seeds) Seeds get dispersed and spread to different locations. At certain appropriate conditions and time, it germinate to a new plant.  Radicle is the first part to emerge from Radicle is directed downwards while the developing cotyledons and shoot is directed upwards. embryo and Cotyledons are the fist leaves of the directed developing embryo. downwards  Structure of plant ovule : The embryo sac (megaspore) 1. Integuments )‫(الغالف‬: encloses and protects the nucellus and the ovum. 2. Micropyle )‫(فتحة النقير‬: no integuments, an opening for entrance of pollen tube. 3. Nucellus: parenchymatous tissue surrounds the ovum 4. Chalaza the basal part of the nucellus from which the integuments arise Whole structure is attached to placenta by Funicle (c.f., umbilical cord). There are two poles (chalazal end) and (micropylar end) Some ovules have RAPHE Placenta Embryo sac contain 8 nuclei. (3+2+3) Three nuclei at micropylar end (one central, egg cell ------ develops into zygote (embryo) and the two adjacent (synergide) adjust orientation of pollen tube to fertilize egg cell, then they disintegrate. Two central unclei, fuse with the other male gamete to develop into endosperm (nutritive tissue). 2-3 antipodal nuclei which degenerate. (at chalazal end)  Double Fertilization ❑ One sperm unite with egg cell ( to give the embryo, male + female, n+n = 2n) ❑ The other sperm unite with 2 central nuclei to give the endosperm (nutritive tissue, n+2n= 3n) UnfertilizedStructure After of seed fertilization ovule Egg cell in Transformed to a zygote (diploid) which develops in an embryo embryo sac consists of radicle and two cotyledons. Two polar nuclei Triploid cell which proliferate to give the endosperm (nutritive tissue) Nucellus Develops into another nutritive tissue (perisperm) (may degenerate) integuments Form the seed coat (testa) after suberization and/or lignification which protects the seed integument Seed coat Embryo Endosperm  After fertilization of the Ovule Outside Integume Testa nts (Coats) √ Nucell Perisperm us √/X 2ry Nucellus Endosperm (Endosperm √/X Nucellus) Egg Embry o√ Inside Compare with bird egg Development of the seed:  The zygote becomes the embryo with its one (monocotyledons) or two (dicotyledons) a radicle and plumule.  This development may be so rapid and vigorous: the embryo absorbs the contents of the embryo sac and the nucellus producing a large embryo surrounded only by the testa, thus forming a non endospermic or exalbuminous seed.  Another type of development when the embryo develops moderately, but at the same time the cells of the nucellus multiply to form a tissue outside the embryo sac and surrounding the endosperm. This tissue is the perisperm. After fertilization The typical seed has: 1. Integuments form the seed coat (testa) with 2 and/or 3 distinctive marks 1. (Hilum) scar at attachment of ovule to funicle. (scar of different color) 2. Micropyle where there is no testa, through this openeing waters enter through it and radicle gets out of seed through it. 3. (And OR Raphe) a vascular bundle running through the testa. It is formed by the fusion of the funicle with the integument for some distance it runs to reach chalaza where it ramify to other tissues. (line / ridge / furrow) 2. Perisperm originate from nucellus. 3. Endosperm results from fusin of the polar nuclei and one sperm cell. 4. Embryo (from fusion of egg cell and the sperm ell) consists of radicle and cotyledons (one: monocot, two: dicot) Embryo Testa Perisperm Endosperm Always present Always present Present/absent Present/absent Develop in For protection nutritive nutritive whole plant Kernel: All tissues enclosed inside the testa Albuminous seed: contain endosperm ± perisperm Exalbuminous seed: consists of testa and embryo only A typical seed consists of Testa Kernel Embryo: developed from fertilized (egg) ovum Endosperm: surrounds the embryo and is developed from primary endosperm nucleus Perisperm: from the nucellus The kernel is all the layers enclosed within the testa 14  Hilum micropyle Funicle 18 Raphe always extend from hilum to position of chalaza (scratching its surface, elements will be stained red with phloroglucin + conc. HCl) Chick pea is ……… (albuminous/exalbuminous) Chick pea is ………. (monocotyledonous/dicotyledo nous) Mark the positions of micropyle, hilum and raphe.  Micropyle Integuments Nucellus Chalaza Funicle Comment 21  TYPES OF OVULES 1. Atropous [orthotropous]: (orthe: straight) Straight ovule , funicle, chalaza & micropyle on 1 straight line, no raphe (piper) 2. Anatropous: ovule inverted , raphe runs from one end to the other, micropyle adjacent to hilum & chalaza at distal end. (it is inverted 180⁰) (1/2 circumference of the seed) (Helianthus) Raphe: is formed by the fusion of the funicle with the integument for some distance. In raphe, a branch of vascular bundle runs to deliver food to the chalaza. (c.f. Umbilical cord) 3.Amphitropous: (Amphi-: both) ovule partly bent, micropyle & chalaza on a line at right angles to hilum, raphe = half distance from chalaza to micropyle, (1/4 circumference of the seed) (Allismaceae) Rotated 90⁰ * *in above mentioned types = nucellus is straight 4.campylotropous: (campylo: curved) ovule bent upon itself, funicle, chalaza & micropyle close to one another, no raphe & nucellus curved (Leguminosae) What is the type of the following ovules? Types of ovules:  Atropous: No raphe  Campylotropous:  Anatropous: raphe  Amphitropous: Imagine Funicle could be similar to…………. Chalaza could be similar to …………… Nucellus and integuments could be similar to …………………..  Types of embryo Orthoplocous radical bents Straight Incumbent #1 cots & e.g. linseed Accumbent radical bents Cots.fold# radical bents #1 cots midrib #2 cots. Coiled Curved Spiral 27  inccumbent Spiral accumbent orthoplocus coiled orthoplocus straight Accumbent: the radicle is bent against the two cotyledons (fenugreek)Coiled Incumbent: the radicle is bent against one coty;edon only. Orthoplocus: The radicle is bent against the cotyledons and both cotyledons are folded along their midrib. Types of outgrowth:  During the formation of certain seeds, arises an additional growths outside the integument or developed from the integuments. Different names are given to these outgrowths according to their origin and nature.  OUTGROWTHS OF TESTA 1.Arillus: from funicle or hilum, envelopes whole seed as in Cardamom 2.Arillode: from micropyle, covers part or whole seed in nutmeg: mace arises from funicle & micropylar tissue, so= arillus or arillode 3.caruncle: localised fleshy, from tissue in neighbourhood of micropyle & covering it, eg. ricinus 4.strophiole: local enlargement over position of raphe, eg. colchicum 5.wing: membraneous extention, Tuft of hairs: **maybe sessile at the summit eg. apocyanaceae borne on a slender stalk= awn as in strophanthus  The Testa It may be membranous (Almond) , leathery (Linseed) , Hard (nutmeg), Very thick and woody (papaya) Fleshy (Magnolia) 32 Outer surface of testa may be: Longitudinally striated (Almond) Smooth (Linseed) Pitted (Digitalis) Papillosed (Grain of paradise) 33  Reticulated Hairy (Nux vomica) (poppy) Rugged (Cardamom) 34  Microscopical characters  1- Testa and outgrowths , if present.  2- Perisperm.(parenchyma cells containing starch)  3- Endosperm (parenchyma cells containing starch,  4- Embryo. protein, or fixed oils “Nutrient”)  5- Cell contents. (starch, protein, fixed oils) Note: Perisperm, endosperm, embryo cells are similar among different seeds Only Testa cells are different and versatile between different seeds ❖ The testa: formed of one or two integuments; four basic layers can be observed. Epidermis ± hypodermis, Sclerenchymatous layer (protection, rigidity) pigment layer (responsible for color of seed) nutritive or hyaline layer (usually collapsed cells because of food consumed)  The epidermis (4 layers): Mucilagenous Palisade-like Sclereide Prosenchyma  Epidermis Hypodermis Sclerenchyma layer Testa Nutritive layer Pigment layer Endosperm Embryo Reserved food material:  Carbohydrates: Starch, cellulose, hemicellulose  Fixed oil and protein(aleurone grain) Types of aleurone grains:  Aleurone grains are either simple in structure and consist of amorphous mass of protein enveloped by a protein membrane e.g. Leguminous seeds.  they have inclusion embedded in an amorphous ground mass of protein, the whole being surrounded by a denser protein envelope.  globoid Aleurone grains  The ground substance  The ground substance in which the crystalloid, globoid., are embedded, it is quite amorphous and usually finely granular in appearance.  The crystalloids  like the ground substance, of proteinoid matter. They assume a crystalline form but differ from true crystals in the inconstancy shown by their angles and in the fact that, under certain conditions, they swell.  The globoids  rounded or ovoid in shape. They are insoluble in water and in dilute caustic potash, but are soluble in dilute acids and in solutions of various salts.  The calcium oxalate  Prisms, clusters and rosettes References  Elsevier platform  Trease and Evans pharmacognosy 16th edition chapter 41  Fundamentals of pharmacognosy and phytotherapy 2nd edition chapter 3