PLSC 368: Lecture 9



    - Kinds of Cuttings
            a. Stem cuttings
            b. Leaf-bud cuttings (single-eye cuttings)
            c. Root cuttings
            d. Leaf cuttings

    - Totiopotency
            -The ability of an individual cell to reconstitute the entire plant parts and functions
            -Each cell has all the genetic information necessary for plant regeneration

    - Dedifferentiation
            -The capability of previously developed, differentiated cells to return to a meristem


    A. What is Adventitious Root?
            Roots arising from any plant parts other than by the normal development of seedling roots

            Two types:            From preformed roots (aerial roots)
                                         Response to wounding (at cut stem base)

              Root Formation After Wounding
                1. A necrotic plate is formed at wounding site
                    -corky material (suberin) seals the wound
                    -gummy material plugs the xylem
                    -protection against desiccation and pathogens

                2. Living cells behind the plate divide
                    -form a wound periderm (a layer of parenchyma cells)
                3. Initiation of adventitious roots
                    -cells in the region of vascular cambium and phloem divide and become root primodium

              Four Stages of  de novo (anew) Adventitious Root Formation
                1. Dedifferentiation
                    -by specifec differentiated cells
                2. Formation of root initials
                    -dedifferentiated cells near vascular bundles become meristematic
                3. Root primordia are formed
                    -from root initiating cells
                4. Root emergence
                    -vascular tissues are formed and connected to the cutting

    B. Root Formation in Herbaceous Plants
            -Adventious roots originate just outside and between vascular bundles
                The tissue from which roots originate varies
                 i.e.  phloem parenchyma (mung bean, pumpkin)
                       epidermis (crassula)
                       pericyle (coleus)

    C. Root Formation in Woody Perennials
            -Adventitious roots originate from living parenchyma cells in young secondary phloem
                Also from vascular rays, cambium, phloem, lenticels ro pith

                   Site of Adventitious Roots
                    - Just outside the vascular tissue in most woody plants
                    - Phloem ray parenchyma
                    - Callus
                    - Pericycle
    D. Root Formation from Preformed Root Initials (burrknots, rootgerms)
            -Burrknots in cherry
            -Root primordia in Ficus pumila, Golden pothos, salix


     -  Callus forms at the cut end
            under environmental conditions favorable for rooting
     -  Callusing and adventitious rooting independent of each other in most species
     -  In difficult to root species, adventitious roots may form from callus
            i.e. Pinus radiata, Sedum, Hedera helix
                root formation of friable callus may be detrimental
                 (i.e. tissue culture rooting)


    A. Leaf Cuttings with Primary Meristems
            -Foliar 'embyos' (young plants) are resent of leaf margins or bases
            -Leaf cuttings made from leaves containing the latent primary meristems
            -Plants:          Bryophyllum (Kalanchoe)
                                 Tomiea (piggyback plant)*
                                 Comptosorus (walking fern)

    B. Leaf Cuttings with Secondary Meristems
            -New plants are formed on secondary meristems
                Secondary meristems arise from mature cells after wounding

            -Both the roots and shoots are generated (the root from first before the shoots)
                 i.e. African Violet
                        -Endogenous roots from cells between vascular bundles
                        -Exogenous shoots from subepidermis or subepidermal cortex tissues
            -Plants:           Sainpauliaionantha (African Violet)
                                 Sansevieria (snake plant)
                                 Carassula argentea (Jade plant)
                                 Lilium longiflorum (Easterlily) -from scale leaf
                                 Peperomia, Sedum, Ficus, etc.

    - Buds develop from pericycle (between endodermis and phloem) near the vascular cambium
    - Adventitious root formation often more difficult than the formation of adventitious buds
         Adventitious roots form at the base of adventitious shoots on the root cutting

    - Adventitious shoots arise more readily from roots of juvenile plant than from roots of mature plants
    - Plants propagated by rhizomes and stolons (both modified stems) are not root cuttings
    - Plants regenerated from root cuttings may exhibit a new phenotype in case of periclinal chimera
            i.e. Thornless boysenberry and Thornless trailing black berry both produce plants that are thorny when propagated by root cuttings


    - Shoots form at the distal end (nearest the shoot tip)
       Roots form at the proximal end (nearest the crown

    - Reversal of the position of cuttings with respect to gravity does not alter the polarity

    - Small pieces of stem tissues still exhibit polarity effect
    - Auxin movement and distribution involved in polarity
    - Polarity research in NASA spaceships?

       Phytohormones- a group of organic compounds, other than nutrients, produced by plants which, in
                                   low concentrations, regulate physiological processes in growth and development
        Plant Growth Regulators- phytohormones or synthetic compounds that modify plant physiological process

    A. Auxins
            -Natural:       Indoleacetic Acid (IAA)
            -Synthetic:     Indolebutyric Acid (IBA)
                                 Naphthaleneacetic Acid (NAA)
            -Enhances root initiation, activates cambial cells, apical dominance
            -Synergistic to cytokinin,  GA activities
            -Concentration Specific

    B. Cytokinins (promotes cell division)
            -Natural:       Zeatin
            -Synthetic:    Kinetin, Benzyl adenine (BAP)
            -Enhances shoot initiation and development
            -Synergistic to auxins
                Low auxin and high cytokinin------------>adventitious buds
                High auxin and low cytokinin------------->adventitious roots

    C. Gibberellins (GA)
            -Promotes cell elongation, division
            -May inhibit both adventitious bud and root formation
            -Concentration dependent

    D. Abscisic Acid (ABA)
            -Regulates stomatal activity, dormancy
            -Antagonistic to GA
            -Effect on root promotion not well understood

    E. Ethylene (C2H4)
            -Involved in fruit ripening, abscission, dormancy
            -Promotes rooting in intact plant parts
            -Production enhanced by auxin applied

VIII. Effects of Buds and Leaves

    A. Presence of buds on the cutting stimulates rooting
            -buds essectial for rooting (auxin source)

            -removal of buds or a ring of bark below a bud results in no rooting
            -buds of non-rest stage nore stimulatory for rooting
            -after buds are broken, rooting reduced (apple, plum)

    B. Presence of leaves stimulatory to rooting
            -Carbohydrates translocated to root initiation site
            -Auxin source
            -Cuttings containing leaves root better

    C. Rooting Cofactors
            -Synergistic to auxins
            -A group of compounds (polyphenol oxidase, IAA oxidase, etc.) needed
                for activation of root initiation
            -Translocated from leaves to rooting site

    D. Endogenous Root Inhibitors
            -Present more in hard-to-root plants
            -Synthesized in roots and moved upward into shoots
            -Reduce root quantity and quality
                Found in pear, Vitis (grape), Eucalyptus
                Leaching the inhibitors out of cut ends recovers rooting


    - Three Classes:
            1) Rapid rooting        - plants contain all necessary substances required for rooting (cofactors, auxin, etc.)
                                             - roots immediately under favorable environment
            2) Auxin requiring      - plants contain all internal cofactors but lack auxin
                                             - root well when auxin is applies
            3) Cofactor-deficient - one or more cofactors lacking
                                             - auxin application fails to stimulate rooting


    A. Environmental Conditions
            -light intensity and duration

    B. Physiological Status
            -stock plant health and etiolation
            -mineral nutrition

    C. Type of Wood Selected
            1. Rooting difference between lateral and terminal shoots
            2. Proximal vs. distal selections
            3. Flowering vs. vegetative woods
            4. 'Heel' vs. 'nonheel' cuttings     i.e. quince, cuttings with 'heel' better

    D. Seasonal Timing
            -for diciduous woody plants