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Biology of adventitious root formation on cuttings

Biology of adventitious root formation on cuttings. The biology of what actually triggers adventitious root formation is largely unknown… But here’s what we do know…. Adventitious root formation. Roots Arise from tissue other than existing roots (e.g. stems, leaves)

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Biology of adventitious root formation on cuttings

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  1. Biology of adventitious root formation on cuttings

  2. The biology of what actually triggers adventitious root formation is largely unknown… • But here’s what we do know…

  3. Adventitious root formation • Roots • Arise from tissue other than existing roots (e.g. stems, leaves) • Absolutely necessary for cutting propagation to work

  4. Two types of adventitious roots Preformed (latent) Wound induced Develop only after the cutting is taken In response to wounding De novo = “anew” Direct – cells in close proximity to the vascular system (easy-to-root taxa) Indirect – from callus (difficult-to-root taxa) • Root primordia are pre-formed but lie dormant • Emerge in response to environmental conditions • Easy to root species • Salix (Willow) • Hydrangea • Populus (Poplar) • Ribes (Currant)

  5. Emerging preformed root initials of Hedera helix

  6. Preformed adventitious roots on corn

  7. Preformed adventitious roots on Kalanchoepanamensis

  8. Aerial (preformed) roots on Ficus

  9. Two types of adventitious roots Preformed (latent) Wound induced Develop only after the cutting is taken In response to wounding De novo = “anew” Direct – cells in close proximity to the vascular system (easy-to-root taxa) Indirect – from callus (difficult-to-root taxa) • Root primordia are pre-formed but lie dormant • Emerge in response to environmental conditions • Easy to root species • Salix (Willow) • Hydrangea • Populus (Poplar) • Ribes (Currant)

  10. Response to wounding • Outer cells die and form a necrotic plate, wound is sealed with suberin, xylem plugs • Living cells behind the plate begin to divide and form callus (parenchyma cells) • Some cells near the vascular cambium and phloem begin to divide and initiate new adventitious roots (where exactly is still unclear!)

  11. Callus

  12. Response to wounding • Outer cells die and form a necrotic plate, wound is sealed with suberin, xylem plugs • Living cells behind the plate begin to divide and form callus (parenchyma cells) • Some cells near the vascular cambium and phloem begin to divide and initiate new adventitious roots (where exactly is still unclear!)

  13. Direct formation of wound induced roots • Dedifferentiation of parenchyma cells • Formation of root initials from cells near vascular tissue (meristematic) • Formation of root primordia (more organized) • Growth and emergence of the new root, connect to existing vascular tissue

  14. Root initials (slightly organized) Root initial

  15. Direct formation of wound induced roots • Dedifferentiation of parenchyma cells • Formation of root initials from cells near vascular tissue (meristematic) • Formation of root primordia (more organized) • Growth and emergence of the new root, connect to existing vascular tissue

  16. Root primordia (more organized) Root cap Meristematic cells

  17. Direct formation of wound induced roots • Dedifferentiation of parenchyma cells • Formation of root initials from cells near vascular tissue (meristematic) • Formation of root primordia (more organized) • Growth and emergence of the new root, connect to existing vascular tissue

  18. Growth and emergence of new root Root initial

  19. Indirect formation of wound induced roots • Callus formation (non-directed cell division; parenchyma) • Cell differentiation • Root initials • Root primordia • New roots and vascular connections

  20. An important difference Leaf and root cuttings Stem and leaf bud cuttings Have to generate adventitious roots only • Have to generate adventitious roots and adventitiousshoots

  21. Adventitious shoot formation • Arise from any plant part other than terminal, lateral or latent buds on stems • Kalanchoepanamensis

  22. Rubber plant • Adventitious shoot formation is the limiting factor!

  23. References • Principles of Propagation by Cuttings, Dr. Fred Davies, Department of Horticultural Sciences, Texas A&M University, College Station, Texas • Hartman, H.T. and D.E. Kester. 1997. Plant propagation: principles and practices. Sixth ed. Prentice Hall, N.Y.

  24. A word about auxin • Auxins will only speed up and enhance rooting of cuttings. • Difficult to root species or cuttings taken from physiologically mature stock plants may not respond to auxin.

  25. Proximal and distal Distal Proximal

  26. Cone of juvenility • Adult = reproductive • Chronologically “newer” but physiologically “older” Juvenile = vegetative Chronologically “older” but Physiologically “young”

  27. Hardwood Cuttings

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