Plant prop quiz 2

Leaf Cuttings —Adventitious Bud (and Shoot) and Root Formation

-- Leaf Cuttings with Preformed Primary Meristems -- Leaf Cuttings with Wound-Induced, Secondary Meristems

Bud effects on rooting

-In some cases buds may be essential or promotive. - Root promoting compounds are thought to be translocated from buds and/or shoot tips, particularly when cuttings are active and not at rest. -These may include auxin andother root promoting substances.

Stages of root formation (4)

1.Dedifferentiation of cells. 2.Formation of root initials - from cells near the vascular bundles or vascular tissue which have become meristematic by dedifferentiation. 3.Development into root primordia. 4.Emergence of roots through the epidermis and formation of vascular connections between the root primordia and the cutting

Stages 4: Root emergence

1.Developing adventitious roots will push their way through the cortex and epidermis and emerge to be functional roots. 2.Visible roots are evident 3. Cuttings do not need as frequent misting.

Cytokinins

Effective in initiating budsand shoots from leaf cuttings and in tissue culture systems.

Maintaining polarity is important in cuttings.

It still produces shoots at the proximal end,and roots at the distal end regardless of the orientation.

Rooting co-factors.

Non-auxin chemicals that promote rooting have been identified in some species. • These chemical act synergistically with auxin to promote rooting

Adventitious organs

Organs that arise from dedifferentiation of pyarenchyma cells

Auxins

Required for initiation of adventitious roots. Division of the first root initial cells are dependent on applied or endogenous auxin.

Callus Formation:

Rooting and Bud (and Shoot) Callus Formation: Organogenesis - Root Organogenesis - Shoot Organogenesis

IBA and NAA:

Synthetic auxins that have greater stability. Most widely used for rooting stem cuttings.

Polarity

The orientation inherent in a stem or root cutting stem or root cutting

Preformed (latent) root initials

develop naturally on the stem and lie dormant or active growth.

Wound-induced roots

develop only after the cutting is made in response to wounding. Formed "de novo" (= "anew") ex.Corn

Formation of adventitious roots and shoots requires plant cells to

differentiate and develop into a root or shoot system

An adventitious bud is an

embryonic shoot

The distal end

is nearest the stem or root tip

When a potential root initiation site is already present the initial cell divisions

lead to root production in situ

roots tend to grow in what type of rows

longitudal

indirect model (interim period of undifferentiated cell division—i.e., generally

more difficult to root

IAA: Synthetic auxins that have greater stability. Most widely used for rooting stem cuttings.

naturally occurring, very unstable, readily degraded auxin

Adventitious buds & shoots = those that arise from any plant part

other then terminal, lateral or latent buds and stems

Auxin moves in a

polar manner from distal to proximal ends.

Changes in endogenous levels may influence

propigation success

adventitious root formation through direct (cells in close proximity to vascular system—i.e., generally

root easier

Application of cytokinin inhibits

rooting in cuttings.

• Adventitious roots =

roots that arise on aerial plant parts, underground stems (tissues other than the seedling root and its branches).

Dedifferentiation

the ability of previously developed, differentiated cells to initiate cell divisions & form new meristems =adventitious roots and buds

Correlative effect

the control of one organ over the development of another - Bud effects on rooting - Leaf effects on rooting Plant growth regulators play a major role

Endogenous rooting inhibitors.

• Rooting inhibitors have been found in some difficult-to-root species • In some cases differences among cultivars and/or tissues of different ages correlate with the rooting ability of shoots.

Leaf effects on rooting

-The presence of leaves exerts stimulating influence - Carbohydrates are translocated from the leaves. -Auxins and other substances are transported polarly

Stages 2: Formation of root initials (3)

1. Dividing cells organize into a root initial. 2. An apical root tip forms. 3. No vascular connection has formed between the cutting and developing root yet

Stages 3: Root primordium formation (3)

1. Root primordia have a well defined root meristem and root cap 2. The vascular system is forming to connect with the xylem and phloem in the parent stem 3. Root primordia are breaking through the sclerenchyma ring and pushing aside the swollen cortex cells

Order of events to produce wound-induced roots

1. outer, injured cells die 2.a necrotic plate forms and seals the would (suberin) = cork and gum blocks xylem 3. parenchyma cells (callus) form behind plate 4.cells near the vascular cambium divide and produce adventitious roots

Stages 1: Dedifferentiation (2)

1.Cells in the cortex divide. 2. These divisions are polar and ordered and will develop into roots. * = dividing cells in the cortex are random and will not become roots. # = epidermal cells

Low auxin/high cytokinin favors

adventitious buds.

Generally, a high auxin low cytokinin ratio favors

adventitious root formation.

Stem and leaf-bud cuttings only need to produce

adventitious roots

The success of cutting propagation depends upon the development of

adventitious roots and/or shoots that develop from cells and tissues of the plant parts used as the cutting material

Root and leaf cuttings need to develop

both adventitious buds & adventitious roots

At high cytokinin concentration, only

buds and budlike tissue are visible with poor shoot development; roots

The proximal end is

closest to the root:shoot junction.