Summary

Introduction: Plant cuticle is layer covering epidermis of leaves, young tissue and other aerial plant parts. Cuticles protect plants against dessication, UV radiation and various kinds of physical, chemical and (micro)biological agents. Moreover, the cuticle also provides some support. They are produced only by the epidermal cells of leaves, young shoots and all other plant organs that do not have a periderm.

Composition : ( lipids , hydrocarbon polymers impregnated with waxes)

Basic Frame-work: 1) A biopolymer, cutin , and 2) long chain fatty acid( wax).

Cutin is covalently crosslinked polymer of fatty acids. . Cutin monomers may be linked directly to each other or through esterification to glycerol. The cuticle can also contain a non-saponifiable hydrocarbon polymer known as Cutan.

Typical plant wax composition:

primary alcohols, aldehydes, alkanes, fatty acids, esters, and sometimes cyclic compounds like triterpenoids and sterols. In addition, there may be hydroxy-β-diketones, oxo-β-diketones, alkenes, branched alkanes, acids, esters, acetates and benzoates of aliphatic alcohols, methyl, phenylethyl and triterpenoid esters, and many more.

Structure:

Role:

Protection of plant from abiotic and biotic stresses such as pathogen , drought etc.

Extraction:

1) Macerating technique for plant leaves: ( millet , orchardgrass and alfalfa)

Steps- a) use rumen fluid ( mixture of interacting microorganism) as macerating medium full strength or diluted with a nutrient buffer solution in the ratio of 2:5.b) incubate at 39 C for 72 hrs

2) Dewaxed leaf discs ( washing with chloroform) are immersed at room temp. in a solution containing 1g of zink chloride in 1.7ml of hydrochloric acid. 4 to 5 ml reagent per dics( 2 cm 2) is used. Membranes begin to separate after I h1r and the reaction is considered complete if membranes are released oln placing a test disc into a large excess of distilled water. This normally occurs within 2 to 12 hr. ( citrus , ficus).

3) Discs, 1.5 cm in diameter, were punched from the fruits and the cuticles isolated using an aqueous mixture of 2% (w/v) pectinase and 0.2% (w/v) cellulase buffered at pH 3.6. After 5 days of incubation at 30 °C the cuticles were recovered, extensively washed in deionized water, air-dried, and stored for further use. Cuticular waxes were removed by refluxing the isolated cuticles in chloroform:methanol (1:1) for 8 h.( jose et al, 2004). Cutin samples were obtained after hydrolysis of de-waxed cuticles in a 6 M HCl solution for 12 h at 105 °C to remove polar hydrolyzable components and then depolymerized in a 3% (w/v) sodium methoxide solution for 18 h at 100 °C (Luque et al., 1995).

4) Enzymatic degradation— cuticle can be isolated from underlying tissue by enzymatic degradation of cell walls involving 2% pectinase and .2% cellulose at pH 4.5 ( Chaumat and Chamet, 1990 but they did at pH 3.8). ( tomato , pepper , rubber , pear , cleaver , Ivy etc.)

---cuticle washed with water and stored.

Method called chloroform dip removes soluble waxes leaving insoluble thin layer of cutin(Arab.)

Cuticular proteins:

Research:

1) Cuticular layer thickens upon drought stress.2) Wax components do not make a large contribution to the structure observed ( Arabidopsis).3) Most of the studies have been conducted to observe the change in ultrastructure( e.g thickness)

and permeability of cuticle under certain conditions.4) Brassica napus cultivars do not show an obvious cuticle layer at 1 week but at 3 weeks the

presence of a cuticle is seen through autofluorescence. 5) There is a considerable variation between plant species in the way in which the cuticle is

attached to the epidermal cell wall.