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Body Plan of angiosperm seedling
Apical basal pattern, radial pattern, three tissue system
Apical meristems
At tips of roots and shoots there is meristematic tissue that continues to source new cells and differentiates cells as it matures
Protoderm primary meristem
Matures into epidermis
Ground meristem primary meristem
Matures into ground tissues ( parenchyma, collenchyma, sclerenchyma)
Procambium primary meristem
Matures into primary xylem and primary phloem
Differentiation
Process by which cells specialize, controlled by gene expression
Xylem
Water conducting cells, support plant and store food
Secondary xylem
Evolve from the vascular cambium
Secondary vs primary growth
Herbaceous plants only have primary growth but woody (conifers) have secondary growth that happens after reaching maturity by using vascular cambium and cork cambium
Ttracheids pits
Thin modified primary cell walls, allow control over pores, can contain air embolism by closing the pit cell
Vessel elements perforation plates
Perforation plates lack secondary and primary cell walls, ladder like openings or ridges
Differentiation of vessel elements
Secondary cell wall deposition, primary cell wall expands and disintegrates and cell undergoes apoptosis
Fibers
Sclerenchyma cells line trachea ray elements, no protoplast and die at maturity but have thick cell walls
Xylem parenchyma
Adjacent to tracheary elements, water moved from and into these cells along xylem path, water moves out via pits
Phloem
Transports sugar, amino acids, lipids, micronutrients, hormones, proteins, RNA, and signaling molecules
Sieve elements
Principal conducting cells of phloem, cluster of pores joining to adjacent cells
Sieve elements: sieve cells
cells with sieve pores
Sieve elements: sieve tube elements
Only in angiosperms, long vessels with sieve plates at the ends, callose deposition
P protein
Forms a plug in sieve plate in case there’s something in it that needs to be sealed
Forisome
Occur in some legumes, non dispersive p protein body, act as gate keeper for sieve plate
Companion cells
Specialized parenchyma cells, is living at maturity, tightly associated to sieve tube elements, deliver molecules
Mother cell of sieve tube element
Divides forming sieve tube element and companion cell and then p proteins arise in the cytoplasm then one of the cells dies and the other remains