1/13/2010 1 Found in Tracheophytes Complex Tissue Found in some seedless plants Cell types and development Principal water conducting tissue Support Storage Primary xylem--procambium Primary xylem--procambium Secondary xylem—vascular cambium 1. Tracheary elements– tracheids and vessels -- elongated --lignified secondary walls --dead at maturity --dead at maturity TRACHEIDS vs. VESSELS --which is imperforate and only have pit pairs in their common wall? --which has perforations?
Transcript
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Found in TracheophytesComplex Tissue
Found in some seedless plants
Cell types and development
Principal water conducting tissueSupportStoragePrimary xylem--procambiumPrimary xylem--procambiumSecondary xylem—vascular cambium
1. Tracheary elements– tracheids and vessels-- elongated--lignified secondary walls--dead at maturity--dead at maturity
TRACHEIDS vs. VESSELS--which is imperforate and only have pit pairs in
their common wall?--which has perforations?
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Lacking both P and S wallsPart of the wall bearing perforation ---PERFORATION PLATEWhere is perforation plate located?Perforation Platea. simpleb. multiple
- sclariform-reticulate-foraminate
Multiple perforationsCommon in tropical high mountain florasTemperate and mild mesothermic climate
ScalariformNon-seasonal mesic habitats
Vessel- continuous tube; may contain at least or hundreds or thousands of vessel elements
Wider vessels– roots; lianasThe basipetal increase in diameter is accompnained
by decrease in density
Pits– simple and borderedoccur in latest formed primary xylem;
*aspirated condition-- crassula ( thickening of ML and P wall)
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Vessels vs. tracheids?Vessel pit membrane vs. torus-margomembrane (conifers tracheids)?Wide vs. narrow vessels?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 embolisma. Wide vesselb Narrow b. Narrow
vesselc. Tracheid
conifer
AIR SEEDINGWhen tension exceeds the surface tension at the air-water meniscus spanning the pores in p g pthe pit membrane, air may be pulled into a functional conduit
2. Supporting elements– FIBERS* fiber-tracheids* Libriform fibers* Septate fibers (eudicots and tropical hardwood) Septate fibers (eudicots and tropical hardwood)
– retain protoplast at maturity--storage of reserve materials-- gelatinous fibers
3. Parenchyma* ray parenchyma and axial parenchyma (2 X)
-- lignified S walls-- simple pits almost alwaysp p y
* storage: starch, fats, tannins or crystals* tyloses– secreted by parenchyma to vessel elements
(contact cells)-- may be hormone-induced or defense mechanism
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Tracheid -- more primitiveTracheary elements*less specialized state: conduction and support combined (tracheids)combined (tracheids)*more specialized – two lines of specialization diverged (vessel- conduction; fibers--support)
Tracheids fiber-tracheids fibersGoing towards mechanical function
1. Sieve elements2. Parenchyma3. Fibers4 Sclereids4. SclereidsMay be present in phloem also:Laticifers, resin ducts, various idioblasts
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Presence of sieve areas (walls with pores)enucleated
a Sieve cells –less specializeda. Sieve cells –less specializedb. sieve-tube elements or members (only
angiosperms)
Modified primary pit fieldsConnecting strands– contents of ports
connect protoplasts of neighboring sieve elementselementsPresece of CALLOSE in each poreThicker connecting strands
Ordinary primary pit fields—less thicker
Thin primary wallPresence of sieve plates
*Sieve plate– wall part bearing sieve areas that are larger than those on other wall parts of the
llsame cellProtoplasts contain P-protein (slime)Associated with companion cells
*companion cell-- specialized parenchyma cells closely related to sieve tube ontogenetically and functionally
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Located at End walls Simple or compoundSieve pores are lined with CALLOSECalloseCallose-- apparently plays a role in sieve pore development
Changes in appearance of plastidsstroma becomes less dense; thylakoids are
sparseAppearance of P-protein (eudicots)Appearance of P protein (eudicots)
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 throughout the elementNo sieve platesElongated and tapering at endsElongated and tapering at endsGymnosperms and vascular cryptogams
Derived from the same mother cell as their associated sieve tube elementsContains many ribosomes, ER, mitochondria, plastidspNucleus prominentInformational molecules, ATP , proteins–are supplied to sieve tube elementsLength of life same as sieve tube members
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gymnospermsDevelops from phloem parenchyma or phloem ray cellsStain intensely with cytoplasmic stainsStain intensely with cytoplasmic stainsConnected physiologically and morphologically to sieve cellsHas connections with sieve cells and lacks starch
Gradual localization of highly specialized sieve areas to the end walls of elementsGradual changes in the position of the endwallfrom very oblique to horizontaly qGradual change form compound to simple onesGradual reduction of sieve areas on the side walls of the elements
Protophloem-no companion cells-sieve tube (ST) elements active for short periodperiod-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 widerlonger and wider- with distinct sieve areas-companion and parenchyma present (eudicots; monocots no parenchyma)- lacks fibers (eudicots
