Shoot and root apical meristem

Developmental stages or evolution of plant kingdom and their types, shoot and root apical meristem

1. Developmental Biology Presentation by Karthi.M Topic: Organization of shoot and root apical meristem

2. Paleozoic Era The Paleozoic Era started 542 million years ago ,ended 251 million years ago The era is usually broken down even further to six main periods. Cambrian: 542 to 488.3 million years ago Ordovician: 488.3 to 443.7 million years ago Silurian: 443.7 to 416 million years ago Devonian: 416 to 359.2 million years ago Carboniferous: 359.2 to 299 million years ago Permian: 299 to 251 million years ago

3. Introduction It is almost a point of definition for the algae that they are aquatic plants, although some of them have invaded moist habitats on land. The useful fossil record begins with the Cambrian period of the Paleozoic Era, over 500,000,000 years ago. Cambrian record, so far as plants are concerned, consists entirely of a wide variety of algae and bacteria. In fact, the early Paleozoic is often referred to as the Age of Algae and Invertebrates. But fossils from the Silurian period, beginning about 360,000,000 years ago This include primitive land plants and it is probable that their first appearance was in the preceding period, the Ordovician. When these first colonists left the waters to invade the more difficult.

4. ………… But more varied habitats on land, the algae remained the dominant members of the earth’s flora. But soon the land dwellers surpassed their aquatic progenitors. One of the crucial problem had to e solved before plants could invade the land was the protection of the zygote against drying. In all land plants, this is accomplished, with important differences in the details, by the retention of the zygote and the developing embryo with in the sex organs of the maternal plants. For this reason, the land plants are known collectively as the subkingdom Embryophyta .

5. The Meaning Of Evolution Is the process of change in living populations. The study of evolution – fundamentals branches of biology – Evolutionary biology It is the study of biology as a historical science, or the study of living systems as they change through time All living systems are products of evolutionary history

6. Evolution Of The Plant Kingdom Plants and their classification Algae Bryophytes Vascular Land Plants Plants with N aked Seeds Flowering Plants

7. Phylogeny Of The Eukaryotes Amoeboid and flagellated protozoans Origin of chloroplasts Red algae ( Rhodophyta ) Eukaryotic algae chrysophyta Brown algae( Phaeophyta ) P yrrophyta Euglenophyta Xanthophyta Green algae( chlorophyta ) Mosses and liverworts(bryophyte) VASCULAR LAND PLANTS( Tracheophyta ) Ciliated protozoans (ciliate) TRUE FUNGI( Eumycota ) Slime molds Cnidaria OTHER MULTICELLULAR ANIMALS Mesozoa Sponges( Porifera )

8. Plants and their classification International Rules of Botanical Nomenclature specify that the plant kingdom is to be separated into ‘divisions’ rather than ‘phyla’. Eichler (1883) and his contemporaries divided the entire plant kingdom into four divisions, as follows: The kingdom plantae contains only those eukaryotic organisms possessing chlorophyll pigments, plastids and also usually a cell wall . The ancestry of the plants is still an unsettled question

9. Division Thallophyta : plants without embryos. class Algae: Thallophytes containing chlorophyll class fungi: Thallophytes without chlorophyll Division Bryophyta : plants with embryos but without vascular tissues: mosses and their relatives Division Pteridophyta : vascular plants without seeds: ferns, horsetails, club mosses and their relatives. Division Spermatophyta : seed plants class Gymnospermae : seed plants without flowers, the seed being naked rather than enclosed in an ovary class Angiospermae : flowering plants, with the seeds protected in an ovary.

10. ……….. The embryophyta include the traditional divisions Bryophyta , Pteridophyta and spermatophyte. Klein and Cronquist (1967) have re-examined the classification of thallophytes and Cronquist,Takhtajan and Zimmerman (1966) have similarly re-examined the classification of the embryophytes . Division Pyrrophyta : dinoflagellates and cryptomonads Division Chrysophyta : golden-brown algae and diatoms Division Euglenophyta : euglena and its relatives Division Rhodophyta : red algae Division Phaeophyta : brown algae Division Chlorophyta : green algae Euglena Brown algae Red algae Diatoms

11. Bryophytes The phylum bryophyta is a relatively small group comprising the mosses, the liverworts and the hornworts. These are the amphibians of the plant world. They have met only minimum requirements of adaptation to the terrestrial environment. They are restricted to wet habitats and all of them require water for reproduction The embryos – multicellular-retained with female sex organs- it protecting them from drying.

12. All of the aerial parts of the plant are covered by a waxy cuticle which protects the plant against drying

13. Phylogeny of the bryophytes Bryophytes of the many characters which they share with the green algae. It is highly probable that the bryophytes were derived from an ancestor among the green algae. One group of bryophytes, the hornworts, suggests relationships to higher plants. While the gametophyte is a small, simple thallus , the sporophyte is larger It is well supplied with chlorophyll But still depends upon the gametophyte for absorption of water and minerals from the substrate

14. The capsule has a central axis of elongate cells which suggests vascular tissue. The epidermis has stomata like those on the leaves of vascular plants. With such an array of traits suggesting those of vascular plants, it is difficult to avoid the inference. that modern hornworts may be but little changed from an ancestral stock by which bryophytes gave rise to vascular plants. This inference appears to misleading, for vascular plants appear in the fossil record in the SILURIAN. The bryophytes appear more than 100,000,000 years later. Obviously if these data are correct, bryophytes cannot be ancestral to tracheophytes . So the weight of opinion among botanists now favors direct origin of the vascular plants, the phylum Tracheophyta , from a chlorophytan ancestor.

15. The Shoot Apical Meristem Shoot system: above ground structures of plants, leaves, buds, stems, flowers and fruits Nodes: where leaves are located Internodes: the spaces between nodes Buds: terminal, lateral, accessory Terminal Buds: located at the tip of the stem Terminal bud scar: indicate the amount of growth over the past year Lateral Bud: found at the side of a stem Accessory Buds: found in pairs and are located beside terminal or lateral buds

16. meristems Tissues of the stem capable of cell division Apical Meristem: found at the tip of the stem Lateral Meristem: found surrounding the stem Growth at the apical meristem is called as primary growth. The 3 types of tissues, apical meristem will be connect. Protoderm : will eventually make the epidermis of the stem. This is the outer protective covering of the stem. G round meristem: will make the different types of ground tissue. Parenchyma: stores water and food Collenchyma: supports young stems and roots Sclerenchyma: hard protection Procambium : will make the vascular tissue. It consist of both xylem(carries water) and phloem(carries food)

17. The Shoot Apical Meristem Contains Different Functional Zones and Layers It consists of different functional regions that can be distinguished by the orientation of the cell division planes and by cell size and activity The angiosperm vegetative shoot apical meristem usually has a highly stratified appearance, typically with three distinct layers of cells These layers are designated L1 , L2 , and L3 , where L1 is the outermost layer Cell divisions are anticlinal in the L1 and L2 layers; that is, the new cell wall separating the daughter cells is oriented at right angles to the meristem surface Cell divisions tend to be less regularly oriented in the L3 layer Each layer has its own stem cells, and all three layers contribute to the formation of the stem and lateral organs Active apical meristems also have an organizational pattern called cytohistological zonation . Each zone is composed of cells that may be distinguished not only on the basis of their division planes, but also by differences in size and by degrees of vacuolation

18. The shoot apical meristem generates the aerial organs of the plant . (A) This longitudinal section through the center of the shoot apex of Coleus blumei Shows the layered appearance of the shoot apical meristem Most cell divisions are anticlinal in the outer L1 and L2 layers, while the planes of cell divisions are more randomly oriented in the L3 layer. The outermost (L1) layer generates the shoot epidermis; the L2 and L3 layers generate internal tissues. (B) The shoot apical meristem also has cytohistological zones, which represent regions with different identities and functions The central zone contains the stem cells, which divide slowly but are the ultimate source of the tissues that make up the plant body The peripheral zone, in which cells divide rapidly, surrounds the central zone and produces the leaf primordia (A ©J.N. A. Lott/Biological Photo Service.).

19. The center of an active meristem contains a cluster of relatively large, highly vacuolate cells called the central zone . The central zone is somewhat comparable to the quiescent center of root meristems. A doughnut-shaped region of smaller cells, called the peripheral zone , flanks the central zone. A rib zone lies underneath the central cell zone and gives rise to the internal tissues of the stem. These different zones most likely represent different developmental domains. The peripheral zone is the region in which the first cell divisions leading to the formation of leaf primordia will occur. The rib zone contributes cells that become the stem. The central zone contains the pool of stem cells, some fraction of which remains uncommitted, while others replenish the rib and peripheral zone populations (Bowman and Eshed 2000).

20. The underground part of the plant is called root system. The underground main axis of the plant body is called root. It is the prolongation of radicle of the embryo. It is positively geotropic or negatively phototropic. It is not differentiated into nodes and internodes. It is non- chlorophyllous or brown coloured. It does not possess leaves, buds, flowers and fruits. Lateral roots are produced from main axis in acropetal succession. Lateral roots are formed from inner region of the main axis ( pericycle ). So these are called ENDOGENOUS ORGANS. Root System

21. The small hair like outgrowth present on the tips of lateral roots and main axis are called ROOT HAIRS. Root hairs are exogenous organs. Root hairs are found in mesophytes and xerophytes and absent in hydrophytes. The protective layer present around the root tip is called ROOT CAP. Root cap is made up of a dead tissue called CALYPTROGEN. Hence it is also called CALYPTRA. It is also well developed in mesophytes and xerophytes, absent in hydrophytes. In free floating hydrophytes root pockets are present .

22. Types of root system Tap root system The central main axis is called tap root. Tap root is formed by the prolongation of radicle of the embryo Lateral roots are produced obliquely in all directions from tap root in acropetal succession. It is most commonly found in DICOTYLEDONS. Fibrous root system or adventitious root system A bunch of new roots are produced from the base of the stem as fibres. So these roots are called fibrous roots and the root system is called fibrous root system. In this, roots are not formed from radicle. So these are aslo called adventitious roots, and the root system is called adventitious root system. It is most commonly found in MONOCOTYLEDONS. In angiosperms two types of root systems are present. They are: 1.Tap root system 2.Fibrous root system or Adventitious root system

23. The Root Tip Has Four Developmental Zones

24. Meristematic zone : lies just under the root cap quarter of a millimetre long root meristem generates only one organ, the primary root It produces no lateral appendages.

25. Elongation zone: site of rapid and extensive cell elongation Although some cells may continue to divide while they elongate within this zone the rate of division decreases progressively to zero with increasing distance from the meristem.

26. M aturation zone: cells acquire their differentiated characteristics Cells enter the maturation zone after division and elongation have ceased Differentiation may begin much earlier but cells do not achieve the mature state until they reach this zone radial pattern of differentiated tissues becomes obvious in the maturation zone

27. Root Apical Meristems Contain Several Types of Stem Cells The patterns of cellular organization found in the root meristems of seed plants It is substantially different from those ob served in more primitive vascular plants All seed plants have several stem cells I nstead of the single stem cell found in P lants such as the water fern Azolla . However , they are similar to Azolla

28. The Arabidopsis root apical meristem has the following structure : quiescent center is composed of a group of four cells A lso known as the center cells in the Arabidopsis root meristem quiescent- center cells in the Arabidopsis root usually do not divide after embryogenesis cortical–endodermal stem cells: It form a ring of cells that surround the quiescent center . These stem cells generate the cortical and endodermal layers They undergo one anticlinal division (i.e., perpendicular to the longitudinal axis ) these daughters divide periclinally (i.e., parallel to the longitudinal axis) to establish the files that become the cortex and the endodermis

29. each of which constitutes only one cell layer in the Arabidopsis root columella stem cells : the cells immediately above (apical to) the central cells They divide anticlinally and periclinally to generate a sector of the rootcap known as the columella root cap–epidermal stem cells: are in the same tier as the columella stem cells but form a ring surrounding them Anticlinal divisions of the root cap–epidermal stem cells generate the epidermal cell layer Periclinal divisions of the same stem cells, followed by subsequent anticlinal divisions of the derivatives, produce the lateral root cap

30. stele stem cells: A re a tier of cells just behind the quiescent- center cells These cells generate the pericycle and vascular tissues The stem cells, together with their immediate derivatives in the apical meristem, are called the promeristem (From Schiefelbein et al.1997, courtesy of J. Schiefelbein , © the American Society of Plant Biologists, reprinted with permission.)  

31. Reference 1. Book Title :Plant Physiology:Zeiger and Taiz , Edition-3 rd 2002,Publishers:sinauer associates Massachusetts, Page no:Chapter 16:340,350-352,354,356. 2. http :// www.els.net/WileyCDA/ElsArticle/refId-a0020121.html 3.shoot system review: https :// www.youtube.com/watch?v=pSMwZJS9JfE 4.Root system review: https ://www.youtube.com/watch?v=pSMwZJS9JfE