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Submitted By:
Deepak Das
Roll No
M.Sc. Life Sciences (Specialization in Plant Sciences)
Contents
• Introduction
• Meaning of Telome Theory
• Elementary Processes
• Concept of Telome Theory in Evolutionary
processes
• Merits
• Demerits
Introduction
Aquatic plants → Land plants
Early vascular land plants
Evolved from
Rhynia
Rhynia
• Telome theory was first proposed by –
Walt Zimmermann in 1930
• Based upon : Fossil record
• Evolutionary modification :
 True Leaf
 True Stem
 True Root
 Complex Vascular System
 Protected Sporangia
Meaning of Telome Theory
• Telome - “Single nerved ultimate terminal portion of a
dichotomising axis”
• 2 types of Telome:
Fertile Telome – Terminated by Sporangium
Sterile Telome – Without Sporangium
• The connecting axex between two telomes - Mesomes
• Several telomes grouped together to form Telome
truss/Syntelome
• Syntelome:
(i) Phylloid Truss – Only Sterile telomes
(ii) Fertile Truss – Only fertile telomes
A figure of Rhyniaceae showing different telomes
Kenrick, P. (2002). The telome theory. Developmental genetics and plant
evolution,
Process of Telome Theory
• Rhynia group of plants underwent certain
evolutionary processes
– Overtopping
– Planation
– Syngenesis
– Reduction
– Curvation
Overtopping
• One of the two
dichotomising branches
outgrows the other and
become larger and
mechanically stronger
• Larger branch forms –
Axis
• Overtopped branch
forms – lateral branches Overtopping process
Planation
Planation Process
• Rearrangement of
telomes and
mesomes from a
three dimensional
pattern to a single
plane
Syngenesis
Syngenesis Process
• Telomes and mesomes
fuse tangentially
• Parenchymatous tissue
is developed in between
• Known as webbing
process
• In stem of Selaginella
polystelic condition due
to - simple
parenchymous webbing
Reduction
Reduction Process
• Activity of terminal
meristem of each
telome supressed
resulting into much
shorter branches
• Responsible for –
Microphyllous
leaves of lycopsida
and Sphenopsida
Needle like leaves
of conifers
Curvation
Recurvation process
• The fertile Telomes
become curved or bend
downwards
• Two sub processes
 Incurvation -
downward shifting of
the sporangia from
terminal or ventral
surface of the leaf in
Pteropsida
 Recurvation -
downward bending of
the sporangia occurs
along with the
sporangial stalks in
Sphenopsida
Concept of Telome Theory
Origin of Sporophylls in Lycopsida
• Planation of the fertile and sterile Telomes
• Reduction of the mesomes and in number of
spornagia
• Protolepidodendron and Psilotum – like
axillary sporangia and single veined leaves are
evolved
Origin of Sporophylls in Sphenopsida
• Recurvation and Syngenesis processes are
involved
• The intermediate developmental stages are
seen in some fossil genera like Calamophyton,
Hyenia, Protocalamostachys and
Asterocalamites
Origin of Sporophylls in Pteropsida
• Overtopping, reduction, syngenesis and
incurvation are the processes involved
• Pinnately-veined sporophylls with marginal
sori developed by the lateral fusion of
mesomes
• In many ferns, the sori are shifted downwards
due to the incurvation process
Merits of Telome Theory
• Describes the origin and evolution of
sporophytes of land plants
• Structure of the sporophytes of the most
primitive known plants is defined
• The exact relationship between the root, stem
and leaves
• Connects the living and fossil plants.
Demerits of Telome Theory
• Does not explain how a telome-like characteristic
body has been developed [Bower (1935)]
• Telome theory does not explain the whorled or
spiral arrangement of sporangia [Thomas (1950)]
• For origin of Lycopsida, it is somewhat
hypothetical [Andrews (1960)]
• Does not provide an acceptable origin of all leafy
structures
• It does not explain the derivation of the
dictyostelic condition [Stewart (1964)]
Reference
• Beerling, D. J., & Fleming, A. J. (2007). Zimmermann's
telome theory of megaphyll leaf evolution: a molecular
and cellular critique. Current opinion in plant
biology, 10(1), 4-12.
• Kenrick, P. (2002). The telome theory. Developmental
genetics and plant evolution, 365-387.
• O.P.Sharma (2016), Series on “Diversity of Microbes
and Cryptogams – Pteridophyta” (pp 28.1-28.5) New
Delhi, India, McGraw Hill Education Pvt. Ltd.
• Vashishta, Sinha, Kumar (2006), Pteridophyta (pp 32-
36) New Delhi, India, S. Chand & Co Pvt. Ltd.
Telome Theory

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Telome Theory

  • 1. Submitted By: Deepak Das Roll No M.Sc. Life Sciences (Specialization in Plant Sciences)
  • 2. Contents • Introduction • Meaning of Telome Theory • Elementary Processes • Concept of Telome Theory in Evolutionary processes • Merits • Demerits
  • 3. Introduction Aquatic plants → Land plants Early vascular land plants Evolved from Rhynia Rhynia
  • 4.
  • 5. • Telome theory was first proposed by – Walt Zimmermann in 1930 • Based upon : Fossil record • Evolutionary modification :  True Leaf  True Stem  True Root  Complex Vascular System  Protected Sporangia
  • 6. Meaning of Telome Theory • Telome - “Single nerved ultimate terminal portion of a dichotomising axis” • 2 types of Telome: Fertile Telome – Terminated by Sporangium Sterile Telome – Without Sporangium • The connecting axex between two telomes - Mesomes • Several telomes grouped together to form Telome truss/Syntelome • Syntelome: (i) Phylloid Truss – Only Sterile telomes (ii) Fertile Truss – Only fertile telomes
  • 7. A figure of Rhyniaceae showing different telomes Kenrick, P. (2002). The telome theory. Developmental genetics and plant evolution,
  • 8. Process of Telome Theory • Rhynia group of plants underwent certain evolutionary processes – Overtopping – Planation – Syngenesis – Reduction – Curvation
  • 9. Overtopping • One of the two dichotomising branches outgrows the other and become larger and mechanically stronger • Larger branch forms – Axis • Overtopped branch forms – lateral branches Overtopping process
  • 10. Planation Planation Process • Rearrangement of telomes and mesomes from a three dimensional pattern to a single plane
  • 11. Syngenesis Syngenesis Process • Telomes and mesomes fuse tangentially • Parenchymatous tissue is developed in between • Known as webbing process • In stem of Selaginella polystelic condition due to - simple parenchymous webbing
  • 12. Reduction Reduction Process • Activity of terminal meristem of each telome supressed resulting into much shorter branches • Responsible for – Microphyllous leaves of lycopsida and Sphenopsida Needle like leaves of conifers
  • 13. Curvation Recurvation process • The fertile Telomes become curved or bend downwards • Two sub processes  Incurvation - downward shifting of the sporangia from terminal or ventral surface of the leaf in Pteropsida  Recurvation - downward bending of the sporangia occurs along with the sporangial stalks in Sphenopsida
  • 14. Concept of Telome Theory Origin of Sporophylls in Lycopsida • Planation of the fertile and sterile Telomes • Reduction of the mesomes and in number of spornagia • Protolepidodendron and Psilotum – like axillary sporangia and single veined leaves are evolved
  • 15. Origin of Sporophylls in Sphenopsida • Recurvation and Syngenesis processes are involved • The intermediate developmental stages are seen in some fossil genera like Calamophyton, Hyenia, Protocalamostachys and Asterocalamites
  • 16. Origin of Sporophylls in Pteropsida • Overtopping, reduction, syngenesis and incurvation are the processes involved • Pinnately-veined sporophylls with marginal sori developed by the lateral fusion of mesomes • In many ferns, the sori are shifted downwards due to the incurvation process
  • 17. Merits of Telome Theory • Describes the origin and evolution of sporophytes of land plants • Structure of the sporophytes of the most primitive known plants is defined • The exact relationship between the root, stem and leaves • Connects the living and fossil plants.
  • 18. Demerits of Telome Theory • Does not explain how a telome-like characteristic body has been developed [Bower (1935)] • Telome theory does not explain the whorled or spiral arrangement of sporangia [Thomas (1950)] • For origin of Lycopsida, it is somewhat hypothetical [Andrews (1960)] • Does not provide an acceptable origin of all leafy structures • It does not explain the derivation of the dictyostelic condition [Stewart (1964)]
  • 19. Reference • Beerling, D. J., & Fleming, A. J. (2007). Zimmermann's telome theory of megaphyll leaf evolution: a molecular and cellular critique. Current opinion in plant biology, 10(1), 4-12. • Kenrick, P. (2002). The telome theory. Developmental genetics and plant evolution, 365-387. • O.P.Sharma (2016), Series on “Diversity of Microbes and Cryptogams – Pteridophyta” (pp 28.1-28.5) New Delhi, India, McGraw Hill Education Pvt. Ltd. • Vashishta, Sinha, Kumar (2006), Pteridophyta (pp 32- 36) New Delhi, India, S. Chand & Co Pvt. Ltd.