Structure and Development of Plant Body

Structure and Development of Plant Body

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  STRUCTURE & DEVELOPMENTOF PLANT BODY: Internal organization of the plant body By N.Sannigrahi, Associate Professor, Department of Botany, Nistarini College, Purulia(W.B) 723101, India The complex multicellular body of the seed plants, a result of evolutionary specialization is the outcome of a series of gradual developmental changes for the establishment of morphological & physiological differences between the various parts of the plant body. The division, differentiation, dedifferentiation & dedifferentiation are the events happen to establish the present state.
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  Plant Structure
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  STRUCTURE • Through thelife long journey of seed plants, it experiences two kind of structure-Primary & secondary. • Primary-This structure initiates at the juvenile stage when cotyledonary leaves sprout-giving rise to plumule & radicle.The former gives rise to shoot systems & the later gives rise to root system. Whatever be the story, the three type of tissues developed- Epidermal, Ground & Vascular tissues. The epidermal gives the external coverings, the ground as the transition & the vascular for vascular supply.
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  Ontogeny repeats phylogeny:Interaction between Genes & Environment • With about 250,000 known plant species, the angiosperms are most diverse plant groups. • A plant’s structure reflects interactions with the environment in two time scale .Over long term, the entire plant species have, by natural selection, accumulated morphological adaptations that enhance the survival & reproduction, • Over short time, the individual plants exhibit structural responses to their specific environment. • The architecture of the plant is a dynamic process , continuously shaped by plant’s genetically directed growth pattern( Homeotic genes) along with the fine tuning with environment.
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  Internal beauty: Pleasureto anatomists
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  Anatomical comparison
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  Inside the wood
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  Secondary Structure • Afterenjoying a optimum growth stage, the secondary development switches on for increasing the girth of the plant body. This is mediated by secondary meristematic tissues-Vascular cambium & Cork cambium. The vascular cambium as remains within the stealer region popularly brings intrastealer growth & the cork cambium lies in the non-stealer region, brings extra-stealer growth. The intrastealer growth transforms into the secondary xylem called wood & extra stealer region transforms the bark or periderm.
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  Wood-the beauty
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  Three tissue systems
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  Epidermal Tissue system •The dermal tissue or Epidermis is generally a single layer of tightly packed cells that covers & protects all young parts of the plants. Single layered very often interrupted by stomata, continuous layers perform many functions- • Covering layer to protect against mechanical injury • Save evaporation from internal tissues, • Photosynthesis & secretion • Storage house of water of xerophytes • Secretory tissues like nectaries, stomata a etc. • Stomata of different types trichomes hairs, are some modifications.
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  Ground tissues • Inbetween epidermis & Vascular cylinder, cortex is the ground tissues, • Mostly thin walled parenchyma tissues but collenchymas, sclerenchyma and sclerides in addition to parenchyma tissues • Very often formed hypodermal regions and starch sheath • Endodermis , a barrel shaped cells arranged Act as protective coverings and to maintain root pressure, very often storage of starch grains, • Pericycle & pith also become the part of the ground tissues.
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  Primary Vascular tissues •Procambium-the meristematic tissues give morphological vascular units gives first xylem & first phloem separated radially by procambium in stems & leaves and transitionally by promeristem in roots. • Exarch primary vascular bundles consists of three major zones-Xylem(Wood), Phloem(Bast) and cambium • Xylem-Vessels or tracheae, Trachids, Wood fibers and xylem or wood parenchyma • Vessels –annular, spiral, scalariform, reticulate and Pitted • Xylem-primary & secondary either Exarch, endarch or mesarch, it may be protoxylem or metaxylem
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  Phloem • Phloem-may beproto phloem & metaphloem, Primary & Secondary phloem, • Consists of Sieve tubes, companion cells, Phloem parenchyma & phloem fibers or bast fibers • Cambium-Primary & secondary • Vascular bundles-Radial(roots), Conjoint(Collateral & Bicollateral), Concentric • Conjoint Open(Cambium) or closed(No cambium)
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  Different tissues arrangement
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  Dicot VS Monocotstem
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  Leaf anatomy
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  STELE • Central vascularcylinder with or without pith and delimited the cortex by endodermis. • Protostele, siphonostele,Sloenostele, dictyostele, Polycxyclic stele & Eustele • Protostele (Without Pith)- Haplostele, Actinostele , Plectostele & Mixed pith stele, • Siphonostele-Medullated contains a tubular vascular region and parenchymatous central region-Cladosiphonic (Leaf gaps absent) & phyllosiphonic (Leaf gaps & branch gaps present)
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  PHLOEM ANATOMY
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