Stele types. The arrangement of xylem and phloem in plant axes

Transcription

1 Stele types The arrangement of xylem and phloem in plant axes

2 Stele Anything from the endodermis inward The configuration of the vascular tissues in transverse section (=cross section) The configuration of the xylem in transverse section Stele terms are used for stems and roots to describe the vascular system There are three basic stele types in vascular plants

3 Stele types in vascular plants 1. Protostele = solid core of xylem, has no pith, no leaf gaps 2. Siphonostele = hollow cylinder of xylem, has pith, has leaf gaps 3. Eustele = xylem and phloem located in vascular bundles, sympodia, has pith, does not have leaf gaps

4 * Stele types

5 Protosteles Haplostele circular in outline Actinostele star-shaped stele Plectostele plates of xylem Medullated protostele (fossils and some lycopods) has a pith but no leaf gaps

6 * Protosteles * * * * *

7 Protosteles Haplostele found in stems of some ferns (fossil and living), also in roots of higher plants (seed plants), early land plants and Psilotum & Tmesipteris Actinostele found in roots of higher plants and stems of lycopods, Psilotum Note: when in roots the phloem is located in between the xylem arms Plectostele found in stems of lycopods

8 Gleichenia a fern stem (=rhizome) with a haplostele Phloem sieve cells Mixed protostele =has parenchyma mixed with xylem tracheids

9 Actinostele Star-shaped stele Found in roots of higher plants Ranunculus root x.s.

10 Actinostele Ranunculus (buttercup) root x.s. Psilotum axis

11 pericycle Endodermis x x x ph ph Developing root Suberized endodermal cell Casparian strip (suberin) mature root

12 Plectostele Lycopodium stem x.s.

13 Steles can change at different stem levels Lycopodium stem x.s.

14 Siphonosteles Siphonostele = hollow cylinder of xylem, has pith, has leaf gaps 1. Solenostele = simple siphonostele with few gaps (e.g., one at a time) stem produces few leaves or one leaf at a time 2. Dictyostele = highly dissected siphonostele (e.g., one producing several leaves at a time, therefore, many gaps This stele type is common in ferns (stems)

15 Fossil solenosteles

16 Solenostele Leaf gap pith stele cortex Adiantum (fern) rhizome x.s.

17 Amphiphloic siphonostele phloem =phloem on both sides of the xylem x pith

18 Dictyostele Polypodium (fern) rhizome (=stem)

19 Osmunda rhizome DICTYOSTELE

20 Osmunda ectophloic dictyostele = phloem on the outside of the xylem only

21 Lycopodium stem in l.s. Giving off leaf traces plectostele

22 Vascular plant steles Medullated Protostele *** *** Note: this is a mistake in your textbook p. 395 (should be as on this slide)

23 Eustele Has pith, NO leaf gaps Ring of vascular bundles e.g., Helianthus (sunflower) pith Found in dicot stems (a group of flowering plants) & Gymnosperms (seed plants such as conifers)

24 Eustele Monocot root

25 Atactostele Scattered vascular bundles in ground tissue no pith per se Corn Zea mays Stem Stele type found in Monocots= Grasses, orchids, aroids, Lilies, rushes, sedges

26 A P I C A L M E R I S T E M Coleus Leaf primordia Shoot apex T H E G R O W I N G T I P

27 l.s. shoot apex Plants grow in length by divisions of cells at apical meristems sa

28 Primary tissues Those tissues produced at an apical meristem; responsible for growth in length of a plant Maturation of these cells and their differentiation (differentiation = becoming different) All cells at the apex in a seed plant are identical in appearance: small, cuboidal, nucleate. Later they become different Primary tissues include: pith, cortex, epidermis, primary xylem, primary phloem, endodermis, pericycle

29 Shoot apex Seed plant Non-seed plant Apical cell

30 Apical cell division Equisetum apical cell

31 Secondary growth Growth produced at a lateral (rather than apical) meristem; responsible for the growth in diameter of a plant E.g.s, wood=secondary xylem, secondary phloem, periderm=bark Not all plant groups have secondary growth; often herbaceous plants do not There are 2 lateral meristems in typical seed plants vascular cambium phellogen (cork cambium)

32 Vascular cambium The lateral meristem that produces secondary xylem (wood), secondary phloem, and vascular rays A ring of meristematic cells that forms between the xylem and the phloem (in residual procambium) and in the ground tissue (parenchyma) between the vascular bundles Produces secondary xylem toward the inside and secondary phloem toward the outside, vascular rays in both directions

33 Secondary growth Tissues produced by a lateral meristemgrowth in diameter of the stem/root

34 Vascular cambium produces secondary xylem & phloem (conducting cells) & vascular rays (parenchyma) Secondary xylem = wood Lateral meristems Phellogen = cork cambium produces the bark system (periderm)

35 Vascular cambium formation in gymnosperm or eudicot eustele

36 Vascular cambium in the stem

37 Origin of the vascular cambium In woody shoots the vascular cambium arises from residual procambium between the xylem and phloem of the vascular bundles (=fascicular cambium) and from the parenchyma cells between the bundles (=interfascicular cambium) A ring of meristematic cells

38 Vascular cambium Produces secondary xylem toward the inside Secondary phloem toward the outside Vascular rays (parenchyma) in these two tissues Contains two types of initials that give rise to secondary tissues 1. fusiform initials 2. ray initials

39 Vascular cambium t.l.s. Give rise to vascular rays Give rise to xylem and phloem conducting cells (tracheids and sieve cells or sieve tube elements)

40 vc Ph fibers 1x 1ph

41 Secondary tissues are produced in radial rows Pinus Pseudotsuga Transition from earlywood to latewood

42 1x 2x 2ph p Vascular cambium periderm

43 3 year old stem

44 Cell divisions in the vascular cambium Multiplicative = anticlinal division-adds to the width of the vascular cambium to keep up with the growth in diameter Additive = periclinal division-produces the mother cells

45 Vascular rays are living parenchyma cells x.s. width of rays seen r.l.s. height of rays seen

46 Uniseriate, biseriate, and multiseriate rays Carpinus t.l.s. height and number of cells wide seen in rays

47 Periderm Protective tissue Secondary origin Called bark-or the bark system Consists of 3 parts Phellogen = cork cambium = lateral meristem Phellem = cork-produced to outside-cells suberized and sometimes also lignified Phelloderm = parenchyma-likeproduced toward the insideusually thin-walled cells

48 Stages in periderm formation

49 ph ph=phellog pd=phellod pl ph pd ep pl

50 Fate of the epidermis and cuticle is to be sloughed off the outside of the stem as phellem produced

51 Cork cells = PHELLEM Cork cambium = PHELLOGEN Cork parenchyma = PHELLODERM PERIDERM

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