UT Arlington BIOL BIOL 3427 - Embryo (3 pages)

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Embryo



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Embryo

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Pages:
3
School:
University of Texas at Arlington
Course:
Biol Biol 3427 - Plant Science
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EMBRYO DEVELOPMENT When a pollen grain fertilizes an ovule inside of the ovary development of the embryo begins Embryonic development occurring within the growing seed creates a new individual from a fertilized egg The embryo goes through several increasingly complex stages as its mitotic divisions continue These stages include the early proembryo the globular stage the heart stage cotyledons begin to emerge the torpedo stage differentiation of the vascular tissues begin and finally the mature embryo The endosperm of most developing seeds is at first non cellular or liquid In both corn and coconuts a portion of the endosperm remains liquid after the outer part of the endosperm has become cellular After the endosperm has become cellular it begins to convert available nutrients into insoluble reserves such as starch proteins and vegetable oils storing up these products for the future use of the embryo during seed germination The final important feature of embryo development within the seed is the cessation of growth when the embryo attains full size This is commonly called embryo dormancy This is a temporary physiologically imposed dormancy If it fails the embryo continues to grow and the seed germinates within the fruit the seed becoming useless as a means of reproduction 1 Obtain slides of various stages of Capsella embryo development Identify as many of the following stages as you can globular heart shaped torpedo and mature 2 Compare what you see to slide pictures of embryo development 3 Examine a prepared slide of a corn grain Identify the endosperm cotyledon coleoptile root root cap coleorhizae and shoot apical meristem Seedling Development A typical seed consists of 1 Embryo the young plant within the seed consisting of a Epicotyl will form the leaf of the new plant b Hypocotyl will form the stem of the new plant c Radicle will form the root of the new plant 2 Endosperm food reserve derived from fertilized polar nuclei 3 Cotyledons will serve as food for the sprouting plant 4 Seed coat a structure derived from the wall of the ovule to protect the inner parts 5 Hilum the funicular scar on the seed coat 6 Micropyle a hole through the seed coat See if you can identify these structures by looking at the seeds you dyed to test for viability There are two types of seedling development epigean and hypogean In epigenous development the cotyledons emerge from the soil In hypogenous development the cotyledons remain in the soil Look at the corn and pea seedlings and see if you can determine which kind of development these plants undergo 1 Early development of Capsella The asymmetric division of the zygote gives rise to the embryo and the extra embryonic suspensor through which nutrients are transported to the embryo 46 The suspensor also pushes the embryo into the lumen of the embryo sac 47 In later development the uppermost cell of the suspensor gives rise to the hypophysis of the embryo 48 which takes part in developing the root cap and tip The embryo is simple and lacks some structures present in the mature plant However the shoot apical meristem from which all later above ground meristems are derived becomes established at this stage The various appearance of the embryo at various stages has been used to provide a context for discussing developmental events Their names are given here In the following images the descendants of the apical cell are shown in yellow and the descendants of the basal cell are shown in pink from Chun Ming Liu Embryogenesis Plant embryogenesis begins with an asymmetric cell division resulting in a smaller apical terminal cell and a larger basal cell This first asymmetric division provides polarity to the embryo Most of the plant embryo develops from the apical terminal cell The suspensor develops from the basal cell The suspensor anchors the embryo to the endosperm and serves as a nutrient conduit for the developing embryo Further cell division leads to the globular stage The three basic tissue systems dermal ground and vascular can be recognized at this point based on characteristic cell division patterns The globular shape of the embryo is then lost as the cotyledons embryonic leaves begin to form The formation of two cotyledons in dicots gives the embryo a heart shaped appearance In monocots only a single cotyledon forms Upright cotyledons can give the embryo a torpedo shape and by this point the suspensor is degenerating and the shoot apical meristem and room apical meristem are established These meristems will give rise to the adult structures of the plant upon germination Further growth of the cotyledons results in the torpedo and walking stick stages At this point embryogenesis is arrested and the mature seed desiccates and remains dormant until germination


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