Plant Cell Walls - 8  
311 Syllabus

The Cell Wall is a Barrier to Pathogens  & Environmental Insults (Drought, Heat, Cold)

This is especially true for the Epidermis due to the presence of Cutin and Wax.

Wax is the outermost layer of Epidermal cell walls.

The Cuticle lies just below the wax. Thus, the wax is called Epicuticular (Epi means above).

These prevent the evaporation of water from leaves and stems.

They also deter fungal attack because they are almost indigestable.

	Asparagus Wax: The wax is the undulating, irregular material. Note the position of the Stomata. Wax further waterproofs Epidermal Cells and forms a protective layer which prevents excess evaporation when the Stomata are open. The wax is often reflective as well.
The images above represent Cuticle on the Epidermis of Cactus Seeds obtained with a Scanning Electron microscope at low magnification (c) and higher magnification (d). The Cuticle has an undulated appearance while the Cell Wall beneath it appears smooth (c)	Fungal Hyphae growing on a Leaf: The fungus has eroded the wax in a zone close to the hyphae. It will have a difficult time digesting the Cuticle which lies just beneath the Epicuticular Wax.

Signaling Molecules are present in the Cell Wall. These are important for normal growth and 
Pathogen Recognition.