differentiation in seed plants. outlines: primary tissues xylem tissue arrangement and...

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Differentiatio n in Seed Plants

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Page 1: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Differentiation in Seed Plants

Page 2: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Outlines:

• Primary Tissues• Xylem Tissue Arrangement and

Differentiation• Stele Evolutionary Development• Leaf Evolutionary Development

Page 3: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Differentiation

• Developmental process by which a relatively unspecialised cell undergoes a progressive change to a more specialised cell

• I.e. the specialisation of cells and tissues for particular functions during development

• Depends on control of gene expression but determined ultimately by the cell’s final position– Cells capable of communicating positional

information from one cell to another

Page 4: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Embryo Differentiation:• Much variation in the patterns of

development observed particularly within the vasculature

Page 5: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary
Page 6: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Xylem Arrangement:

• With respect to the pattern or direction of differentiation of primary xylem from the PROCAMBIUM, 4 relationships are known.

• However, their recognition depends on a distinction between two kinds of PRIMARY XYLEM,

1. PROTOXYLEM

2. METAXYLEM.

Page 7: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

• the first-formed primary xylem,

• its elements usually smaller in diameter,

• differentiates before elongation of the organ has ceased,

• and lignified in annular or spiral fashion.

Protoxylem:

Page 8: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Protoxylem:

Page 9: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

• differentiates after the PROTOXYLEM,

• its elements are larger in diameter,

• they mature only after elongation of the organ has ceased,

• and their secondary wall pattern is usually reticulate or pitted.

Metaxylem:

Page 10: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Metaxylem:

Pits

Page 11: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

• However, there are transitions between protoxylem and metaxylem

• The four patterns of primary xylem differentiation from the procambium are: – EXARCH– MESARCH– ENDARCH– CENTRARCH

Xylem Differentiation:

Page 12: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

EXARCH MESARCH

ENDARCH

CENTRARCH

Page 13: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

• (Greek – “pillar”) The central cylinder, inside the cortex, of roots and stems of vascular plants.

• The term stele sums up the vascular system, associated tissues and the enclosed pith.

• General types of stele that evolved over time: • Protostele:

– Haplostele– Actinostele– Plectostele

• Siphonostele– Dictyotele– Eustele – Atactostele

STELES

Page 14: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Types of stele

Page 15: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Protostele: Haplostele• Protosteles are the simplest and are often

considered the most primitive type of stele.• It is essentially a solid core of xylem

surrounded by a cylinder of phloem, a protostele contains no pith

• Found in most roots and in extinct groups of seedless vascular plants

• If xylem area is circular in crossection it is called a Haplostele (See fig).

Page 16: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Protostele

Page 17: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Protostele: Actinostele• A protostele with radiating arms.

• The central xylem instead of being round becomes a radiated star shaped arm with the protoxylem being found in the arms and the metaxylem being found central.

Page 18: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Protostele

Page 19: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Protostele: Plectostele• Is a protostele in which phloem is

interspersed in masses between the xylem.

• That is, the radiating arms develop more into a plate like structure.

• The xylem although interrupted at a given level, forms a continuous system (see fig.).

Page 20: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Plectostele

Page 21: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

The Siphonostele

• Two main kinds of Siphonotele:– Ectophloic– Amphiphloic

Page 22: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

The Siphonostele: Ectophloic• The siphonostele is widely distributed, occurring

in ferns and in certain gymnosperms and flowering plants.

• In the siphonostele the xylem and the phloem forms a cylinder around a central pith with no gaps.

• The phloem may be both external and internal as it is in many ferns

• In ectophloic siphonosteles the phloem is restricted to the outer surface of the xylem.

Page 23: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

• In this case it is said to be amphiphloic siphonostele, and is sometimes called a solenostele.

Siphonostele: Amphiphloic

Page 24: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

SiphonosteleSiphonostele

Cortex

Page 25: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Siphonostele: Dictyostele

• In a solenostelic stem with short internodes, overlapping of the nodal leaf gaps results in a dissection of the stele (See fig).

• That is, there are one or two leaf gaps in the xylem and phloem created by leaf traces.

• In crossection the stele appears as discrete strands or bundles.

Page 26: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Siphonostele: Eustele• Where the xylem and phloem occur in

discrete collateral (situated side by side) or bicollateral strands or bundles; the arrangement is called a Eustele

Page 27: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Eustele

Page 28: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Siphonostele: Atactostele

• Here the discrete strands of xylem and phloem are scattered through the stem

• This is the arrangement found in monocotyledonous flowering plants.

Page 29: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary
Page 30: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

A. Protostele(haplostele) B. Protostele (actinostele) C. Protostele (plectostele)

D. Siphonostele (ectophloic)

E. Siphonostele (amphiphloic)

F. Dictyostele

H. Atactostele

G. Eustele Derivation of steles Derivation of steles from the primitive from the primitive

protosteleprotostele

Page 31: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Leaf development:

• Leaf Trace:– A vascular bundle branch that

extends from a stem bundle to the base of a leaf, where it connects with the vascular system of the leaf, is called a leaf trace

• Leaf Gap:– the gap in the ground tissue left

behind is called a leaf gap – Occur in more advanced

siphonostelic or eustelic stems

Page 32: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Vascular Arrangements:

Page 33: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

• There are two types of leaves depending on the type of leaf trace:

– Microphyll: A leaf arising out of a leaf trace without any gaps.

– Megaphyll: A leaf arising out of a leaf trace which has a leaf gap.

• In the microphyll the stele of the stem is protostellic with no gaps between the leaf traces.

• In the megaphyll the leaf trace can leave a gap which is filled by parenchymatous tissue. Usually siphonostellic.

Leaf Types:

Page 34: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary
Page 35: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary
Page 36: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Leaf Development (Microphyll):• Microphylls: relatively small leaves with a

single vascular strand, usually associated with Protosteles

• Typical of the seedless vascular plant group – Lycophytes (club mosses)

• Evolutionary development:– Began as scale-like outgrowths with no vascular

tissue (Enation)– Leaf trace then formed, initially at base– Eventually extended from the stele into the

emergent enation microphyll– No leaf gaps formed with the stele

Page 37: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Microphyll Development

Page 38: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Leaf Development (Megaphyll/Macrophyll):• Usually larger than microphylls

• Associated with the siphonosteles of Euphilophytes (which include Ferns and Seed Plants)

• Evolutionary development (Telome Theory):– Began with leafless dichotomously branching

plants– Unequal branching then occurred with some

becoming more dominant than others (“overtopping”) – pseudomonopodal growth

– Subordinate / lateral branches leaf via “planation” & “webbing”

– Associated with leaf gaps

Page 39: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary
Page 40: Differentiation in Seed Plants. Outlines: Primary Tissues Xylem Tissue Arrangement and Differentiation Stele Evolutionary Development Leaf Evolutionary

Recap…

• Three 1o tissues derived from 3 1o cambia– Protoderm Epidermal Tissues– Ground Meristem Ground Tissues– Procambium Vascular Tissues

• Two main kinds of Stele:– Protostele (primitive) Siphonostele

(more advanced)– Atactostele – most advanced

• Leaf development– Primative microphyll– Advanced megaphyll