The epidermis is the surface tissue covering all organs of the plant during primary growth

•  Root

•  Stem

•  Leaf

•  Epidermis in surface view

Functions

•  Protection from desiccation

•  Protection from disease organisms

•  Protection from insect damage

•  Gas exchange

•  Secretion

Origin

•  Epidermis differentiates from the protoderm

•  Usually one cell thick unless there are periclinal division of protoderm cells. Then you have multiple epidermis.

Cuticle and waxes

•  In shoots, the outer epidermal cells are covered with the cuticle.

•  The cuticle contains the lipid cutin, which is largely impermeable to water (and gases).

•  The development of the cuticle is regarded as one of the important evolutionary steps in the origin of the land plants.

•  Some plants have additional wax layers

•  Cuticle thickness and presence of wax layers is partly a function of habitat.

•  Arid climate species tend to have thicker cuticles

•  Mesic and aquatic plants have thinner cuticles

Cell types

•  ordinary epidermal cells

•  guard cells (in pairs) form stomata

•  trichomes

Stomata

•  Stucture of guard cells

•  Mechanism of opening and closing

•  Radial micellation

•  Stomata open when guard cells take up water and expand

•  The stomatal complex

•  The pair of guard cells is often surrounded by special cells that differ in shape from the ordinary epidermal cells

•  These surrounding cells are termed subsidiary cells

•  The shape and placement of subsidiary cells result from the pattern division of protoderm cells leading up to the formation of the guard cells.

•  Stomatal complex type has taxonomic value. Many taxa (genus, family) are characterized by a particular type.

•  Common stomatal complex types

•  Anomocytic. No subsidiary cells. Cells surrounding guard cells are not different that other epidermal cells.

•  Anisocytic. Guard cells surrounded by three subsidiary cells of unequal size.

•  Paracytic. One subsidiary cell on each side of the guard cells oriented parallel to the stoma.

•  Diacytic. One subsidiary cell on each side of the guard cells oriented perpendicular to the stoma.

•  Actinocytic. Several subsidiary cells that radiate from the center of the stoma forming a ring.

Trichomes

•  Trichomes are appendages of the epidermis.

•  Most are hair-like are are commonly called plant hairs.

•  There is a large diversity of forms - examples:

•  Can be unicellular or multicellular

•  Can be simple or branched

•  May have secretory function (glandular hairs)

•  Epidermal "peel" with trichomes

•  Complex trichomes are sometimes called scales

•  Peltate scales on leaves of Elaeagnus (whole mount)

•  Cross section of Elaeagnus leaf showing scale

•  Root hairs

•  Root hairs are simple, usually unicellular trichomes found in large numbers near the tips of growing roots.

•  They greatly increase the surface area of the epidermis that is in contact with the soil solution.

•  They increase the efficiency with which the root can absorb water and mineral nutrients.

•  Trichomes are valuable taxonomically and can aid in plant identification.

•  Trichomes have even been used in forensic science.

•  For example, marijuana (Cannabis sativa) has distinctive glandular and nonglandular hairs that are diagnostic. This has provided evidence in drug-related court cases.

Periderm

•  In plants having secondary growth, the epidermis is temporary. It is replace by the periderm, the secondary dermal tissue.

•  We will cover the periderm later in connection with secondary growth

Delta State University > DSU Sciences > Dr. Tiftickjian > Plant anatomy > Epidermis