Vascular Tissues
2 likes1,037 views
1. Xylem is the water-conducting tissue found in tracheophytes. It is composed of tracheary elements, fibers, and parenchyma cells. 2. Tracheary elements include tracheids and vessels. Tracheids are imperforate while vessels have perforations along their length. 3. Phloem is the food-conducting tissue. It consists of sieve elements, companion cells, and parenchyma. Sieve elements transport sugars and other molecules between source and sink tissues.
Vascular Tissues
- 1. 1/13/2010 Found in Tracheophytes Complex Tissue Found in some seedless plants Cell types and development Principal water conducting tissue 1. Tracheary elements– tracheids and vessels Support -- elongated Storage --lignified secondary walls Primary xylem--procambium --dead at maturity Secondary xylem—vascular cambium TRACHEIDS vs. VESSELS --which is imperforate and only have pit pairs in their common wall? --which has perforations? 1
- 2. 1/13/2010 Lacking both P and S walls Part of the wall bearing perforation --- PERFORATION PLATE Where is perforation plate located? Perforation Plate a. simple b. multiple - sclariform -reticulate -foraminate Multiple perforations Common in tropical high mountain floras Temperate and mild mesothermic climate Pits– simple and bordered Scalariform occur in latest formed primary xylem; Non-seasonal mesic habitats secondary xylem Pit pairs Vessel- continuous tube; may contain at least or In Conifers hundreds or thousands of vessel elements – torus Wider vessels– roots; lianas --margo– flexible The basipetal increase in diameter is accompnained *aspirated condition by decrease in density -- crassula ( thickening of ML and P wall) 2
- 3. 1/13/2010 Vessels vs. tracheids? Vessel pit membrane vs. torus-margo membrane (conifers tracheids)? Wide vs. narrow vessels? CAVITATION --formation of cavities within the conduits resulting in breakage of the water columns --Embolism- air blockage -- CAUSES: Freezing and Drought Arrange the ff. from most prone To least prone to freeze induced AIR SEEDING embolism When tension exceeds the a. Wide vessel surface tension at the air-water b. b Narrow meniscus spanning the p p g pores in vessel the pit membrane, air may be pulled into a functional conduit c. Tracheid conifer 2. Supporting elements– FIBERS 3. Parenchyma * fiber-tracheids * ray parenchyma and axial parenchyma (2 X) * Libriform fibers -- lignified S walls * Septate fibers (eudicots and tropical hardwood) -- simple p almost always p pits y – retain protoplast at maturity * storage: starch, fats, tannins or crystals --storage of reserve materials * tyloses– secreted by parenchyma to vessel elements -- gelatinous fibers (contact cells) -- may be hormone-induced or defense mechanism 3
- 4. 1/13/2010 Tracheid -- more primitive Tracheary elements *less specialized state: conduction and support combined (tracheids) *more specialized – two lines of specialization diverged (vessel- conduction; fibers--support) Decrease in length Inclined transverse end walls Scalariform simple perforation plates Scalariform bordered pitting alternate bordered pitting Vessel outline: angular rounded INCREASED conductive efficiency or safety Tracheids fiber-tracheids fibers Going towards mechanical function 4
- 5. 1/13/2010 Protoxylem differentiates in parts of the Protoxylem primary plant body that have not compeleted few tracheary elements their growth and differentiation in monocots, protoxylem lacunae Metaxylme begins to differentiate in the still Metaxylem growing plant body but matures after elongation is completed. wider tracheary elements Fibers May be non-functional when plants undergo secondary growth 5
- 6. 1/13/2010 Principal food conducting tissue Transports: sugars, amino acids, micronutrients, lipids, HORMONES, FLORIGEN 1. Sieve elements 2. Parenchyma 3. Fibers 4. Sclereids 4 May be present in phloem also: Laticifers, resin ducts, various idioblasts 6
- 7. 1/13/2010 Presence of sieve areas (walls with pores) Modified primary pit fields enucleated Connecting strands– contents of ports connect protoplasts of neighboring sieve a. Sieve cells –less specialized a elements b. sieve-tube elements or members (only Presece of CALLOSE in each pore angiosperms) Thicker connecting strands Ordinary primary pit fields—less thicker Thin primary wall Presence of sieve plates *Sieve plate– wall part bearing sieve areas that are larger than those on other wall parts of the same cellll Protoplasts contain P-protein (slime) Associated with companion cells *companion cell -- specialized parenchyma cells closely related to sieve tube ontogenetically and functionally 7
- 8. 1/13/2010 Located at End walls Simple or compound Sieve pores are lined with CALLOSE Callose -- apparently plays a role in sieve pore development Changes in appearance of plastids stroma becomes less dense; thylakoids are sparse Appearance of P protein (eudicots) P-protein appears as slime plugs at sieve plates upon release of pressure when sieve tubes are severed (sealing of pores of injured elements; immobilize bacteria) Unspecialized sieve areas that are similar Derived from the same mother cell as their throughout the element associated sieve tube elements No sieve plates Contains many ribosomes, ER, mitochondria, Elongated and tapering at ends p plastids Gymnosperms and vascular cryptogams Nucleus prominent Informational molecules, ATP , proteins–are supplied to sieve tube elements Length of life same as sieve tube members 8
- 9. 1/13/2010 gymnosperms Gradual localization of highly specialized sieve Develops from phloem parenchyma or phloem areas to the end walls of elements ray cells Gradual changes in the position of the endwall Stain intensely with cytoplasmic stains from very oblique to horizontal y q Connected physiologically and Gradual change form compound to simple morphologically to sieve cells ones Has connections with sieve cells and lacks Gradual reduction of sieve areas on the side starch walls of the elements *specialization direction: root leaf (highly specialized) Protophloem -no companion cells -sieve tube (ST) elements active for short period -sieve areas difficult to distinguish -obliterated by surrounding cells (ST no nucleus so not able to divide) -remaining parenchyma fibers; collenchyma (leaves) Metaphloem - function for many years (plants without secondary growth) - longer and wider - with distinct sieve areas -companion and parenchyma present (eudicots; monocots no parenchyma) - lacks fibers (eudicots 9
- 10. 1/13/2010 10