The Cuticle, Cutin, Suberin & Waxes-1    
311 Syllabus

By now you should be convinced that the Plant Cell Wall is an extremely important structure. The most fundamental problems facing land plants are the acquisition, translocation and retention of Water.

Typical Primary Cell Walls take up water readily but they also release it readily. Plants produce some chemicals which infiltrate and cover the cellulose fibrils of the wall, and block the passage of water. Some of these may also reflect excess light, and some provide a barrier to pathogens.

The Epidermis is the Tissue which directly confronts the environment. Consequently, it displays many  important surface adaptations. The production of the CUTICLE is one of its most important adaptations.

SEM images of the surface wax for Rose (left) and Convallaria (left). The white material on the surface is Wax. Note the differences in the wax patterns. These can have ecological and taxonomic importance.

The Cuticle is complex. It contains two kinds of Hydrophobic hydrocarbons, Cutin and Wax. The chemical differences between these are not important for this course, but a few important points can be made.

Cutin is the major component of the Cuticle and it is consists of many long chain fatty acids. Remember that fatty acids are major parts of biological membranes. However, the fatty acids in Cutin are stabilized by covalent bonds and are Solid at physiological temperatures.

Wax is a complex mixture of long chain hydrocarbons. These usually crystallize on the surface of the Cuticle. It is often called Epicuticular Wax.

They are extremely hydrophobic and block water movement.

They may also be very reflective. This can prevent the damaging effects of  excess light. You may notice that many "desert plants" (xeromorphs) have a frosty appearance. Some are almost silver or white. Such surfaces reflect light!

Excess light absorption increases the temperature inside plants. This can lead to excess evaporation, and may even cause  physiological trauma.

Consequently, light reflection can be a very important adaptation.

Wax patterns can be diagnostic for plant identification.

Components of the Cuticle are secreted through the outer tangential region of the Plasmalemma. They travel through the outer Cell Wall and solidify on the surface. The exact path and mechanism by which the cuticle forms is still unclear.

The Cuticle is one of the most important adaptations of land plants!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

There are three layers which comprise the Cuticle.

1] The outermost layer is composed by Wax

2] The next region is called the Cuticle Proper and is pure Cutin.

3] The Cuticular Layer is next. This is a mixture of Cutin and Wall Polysaccharides (Cellulose, Hemicellulose).

4] These are underlain by a Cellulose Wall.

Suberin is similar to Cutin in many respects but is chemically distinct. It is located in the Casparian Strip of the Endodermis.

The Casparian Strip is one of the most important adaptations for land plants. We will discuss this later.

Suberin is a principal component of Cork Cell Walls which are part of the Periderm (Outer Bark). The Periderm may replace the Epidermis. It is an important secondary tissue which we will discuss later.

It is also present in Cell Walls at sites of Abscission and Wounding.