biology of adventitious root formation on cuttings
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
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)
• Absolutely necessary for cutting propagation to work
Two types of adventitious roots
Preformed (latent)• 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)
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)
Emerging preformed root initials of Hedera helix
Preformed adventitious roots on corn
Preformed adventitious roots on Kalanchoe panamensis
Aerial (preformed) roots on Ficus
Two types of adventitious roots
Preformed (latent)• 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)
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)
Response to wounding
1. Outer cells die and form a necrotic plate, wound is sealed with suberin, xylem plugs
2. Living cells behind the plate begin to divide and form callus (parenchyma cells)
3. Some cells near the vascular cambium and phloem begin to divide and initiate new adventitious roots (where exactly is still unclear!)
Callus
Response to wounding
1. Outer cells die and form a necrotic plate, wound is sealed with suberin, xylem plugs
2. Living cells behind the plate begin to divide and form callus (parenchyma cells)
3. Some cells near the vascular cambium and phloem begin to divide and initiate new adventitious roots (where exactly is still unclear!)
Direct formation of wound induced roots
1. Dedifferentiation of parenchyma cells2. Formation of root initials from cells near
vascular tissue (meristematic)3. Formation of root primordia (more
organized)4. Growth and emergence of the new root,
connect to existing vascular tissue
Root initials (slightly organized)
Root initial
Direct formation of wound induced roots
1. Dedifferentiation of parenchyma cells2. Formation of root initials from cells near
vascular tissue (meristematic)3. Formation of root primordia (more
organized)4. Growth and emergence of the new root,
connect to existing vascular tissue
Root primordia (more organized)Root cap
Meristematic cells
Direct formation of wound induced roots
1. Dedifferentiation of parenchyma cells2. Formation of root initials from cells near
vascular tissue (meristematic)3. Formation of root primordia (more
organized)4. Growth and emergence of the new root,
connect to existing vascular tissue
Growth and emergence of new rootRoot initial
Indirect formation of wound induced roots
• Callus formation (non-directed cell division; parenchyma)
• Cell differentiation
• Root initials• Root primordia• New roots and vascular connections
An important differenceLeaf and root cuttings• Have to generate
adventitious roots and adventitious shoots
Stem and leaf bud cuttings• Have to generate
adventitious roots only
Adventitious shoot formation
• Arise from any plant part other than terminal, lateral or latent buds on stems
• Kalanchoe panamensis
Rubber plant
• Adventitious shoot formation is the limiting factor!
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.
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.
Proximal and distal
Proximal
Distal
Cone of juvenility
• Adult = reproductive
Chronologically “newer” but physiologically “older”
Juvenile = vegetative
Chronologically “older” but Physiologically “young”
Hardwood Cuttings