plant propagation ch 10; cuttings

How Hormonal Control Affects Adventitious Root and Bud (and Shoot) Formation

For root initiation, the presence of a metabolically active shoot tip (or lateral bud) is normally necessary. This is because it is thought that the bud contains hormones that promote rooting. The shoot tips may be necessary for just a few days (3 or 4) or longer depending on the species. It is important to know when the species that you are taking cuttings from has dormant buds (rest period). If you take cuttings during this time, it will significantly reduce the chance of the cuttings forming roots. • The presence of leaves on cuttings exerts a strong stimulating influence on rooting. Carbohydrates are translocated from leaves during root development. However, like buds, it is thought that the leaves contains hormones that promote rooting.

Lighting Effects on Cutting Propagation

Light Intensity AND Photoperiod AND Light Quality

Adventitious roots are of two types...

Preformed adventitious roots AND Wound-induced roots

Cutting Propagation

most important means for clonal regeneration. Cutting propagation depends on regenerative processes from adventitious organs such as roots and buds. Adventitious organs arise from the dedifferentiation of parenchyma cells; the process of dedifferentiation is the capability of previously developed, differentiated cells to initiate cell divisions and form a new meristematic growing point.

Leaf Cuttings with Wound Induced Secondary Meristems

new plants develop from secondary meristems arising from differentiated cells as a result of wounding. Plant examples - Sansevieria, Sedum, Saintpaulia, and Peperomia.

Temperature Effects on Cutting Propagation

optimum medium temperature for propagation of temperate-climate species is 65ºF - 77ºF; 13ºF higher for warm-climate species. Can reduce temperatures at night depending on species.

Adventitious root formation

roots that arise from any non-root plant tissue such as stems or leaves.

Water Relations and Humidity Control of Cuttings

the water status of cuttings is a balance between transpiration losses and uptake of water. It is directly proportional to volumetric water content of the propagation media. Media should be moist, but not so wet as to lead to anaerobic conditions which causes cutting death. It is also important to reduce water loss from leaves due to transpiration. This can be done by reducing the vapor pressure deficit (VPD) - the difference between the internal cutting leaf vapor pressure and that of the surrounding air.

Callus Formation and Rooting Organogenesis

• Callus - growing mass of unorganized parenchyma cells produced in response to wounding. Usually occurs at the basal end of a cutting during rooting. • Root organogenesis - the process of developing adventitious roots. Changes take place in the cells that lead to the development of the root primordiam whose vascular system is often connected to the parent tissue.

Patterns of Adventitious Root Formation

• Direct root formation - cells in close proximity to the vascular system form roots. Found in most easy-to-root species. • Indirect root formation - nondirected cell divisions, including callus formation, occur for an interim period before cells divide in an organized pattern to initiate adventitious root primordia. Found in most difficult-to-root plants.

Methods to control water loss from leaves are include...

• Intermittent Mist • Nonmisted Enclosures • Fog Systems

Root Cuttings - Adventitious Bud (and Shoot) and Root Formation

• Most often - the root cutting will first produce an adventitious shoot, and later produce roots, often from the base of the new shoot. Example - Sweet potato. • Some species - adventitious buds form readily on roots of intact plants, producing suckers. These can be dug and removed, and then cut into individual plants.

Leaf Cuttings with Preformed, Primary Meristems

a "foliar embryo" forms in the early stages of leaf development from small groups of vegetative cells at the edges of the leaf. As the leaf expands, the foliar embryo develops until it consists of two rudimentary leaves with a stem tip between them, two root primordia, and a foot that extends toward a vein. As the leaf matures, the foliar embryo cell division ceases, and it remains dormant. If the leaf is detached and placed in a moist rooting medium, the young plants break through the leaf epidermis and become visible in a few days. Plant examples - Tolmiea and Camptosorus.

Adventitious bud (and shoot) development

buds and shoots that arise from any plant part other than terminal, lateral, or latent buds on stems. They form irregularly on older portions of a plant and not at the stem tips or in the leaf axils. Unlike dormant buds, adventitious buds do not have a bud trace all the way to the pith. An adventitious bud is an embryonic shoot.

Stages of De Novo Adventitious Root Formation

• Stage I: Dedifferentiation and induction of specific differentiated cells before any visible histological changes .• Stage II: Root initiation formation (early): Increased vascular cambium activity, followed by divisions of dedifferentiated cells near vascular bundles or vascular tissue, that is, with phloem ray parenchyma. • Stage II: Root initial formation (late): Continued cell division of dedifferentiated parenchyma cells forms meristemoids that further develop into root initials. • Stage III: Root primordia formation: root initials develop into a fully organized meristem with a root cap in the stem tissue of the cutting. • Stage IV: Root primordia elongation: Root primordia elongate through the stem tissue, pushing out sclereids in the exterior of the cortex and emerging through the periderm.

Propagation systems are designed to maintain...

•An environment that has low evaporative demand and will minimize transpirational water losses from cuttings to help avoid substantial tissue water deficits .•Acceptable temperatures for the regeneration process. Need to pay attention to both the base and the leaves. •Appropriate light levels that promote photosynthesis and carbohydrate production to maintain both the cutting and promote root initiation.

Phytohormones and Plant Growth Regualtors

•Auxin has the greatest effect on root formation in stem cuttings. •Cytokinins have the best effect on adventitious bud formation in leaf cuttings.