Lecture 13: vasculature

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