Epicuticular wax
Encyclopedia
In botany
, the plant cuticle
is covered by epicuticular wax or bloom mainly consisting
of straight-chain aliphatic hydrocarbon
s with a variety of substituted groups, serving to decrease moisture loss and decay. Common
examples are paraffin
s in leaves of pea
s and cabbage
s, alkyl ester
s in leaves of carnauba palm and banana
, the asymmetrical secondary alcohol 10-nonacosanol in most conifers such as Ginkgo biloba and Sitka spruce
, many of the Ranunculaceae
, Papaveraceae
and Rosaceae
and some mosses, symmetrical secondary alcohols in Brassicaceae
including Arabidopsis thaliana
, primary alcohol
s (mostly octacosan-1-ol) in most grasses Poaceae
, Eucalyptus
and legumes among many other plant groups, β-diketone
s in many grasses, Eucalyptus
, box Buxus
and the Ericaceae
, aldehyde
s in young beech
leaves, sugarcane
culms and lemon
fruit and triterpene
s in fruit waxes of apple
, plum
and grape
These compounds are mostly soluble in organic solvents such as chloroform
and hexane
, making them accessible for chemical analysis, but in some species esterification of acids and alcohols into estolides or polymerization of aldehydes may give rise to insoluble compounds. Solvent extracts of cuticle waxes contain both epicuticular and cuticular waxes, often contaminated with cell membrane
lipids of underlying cells. Epicuticular wax can now also be isolated by mechanical methods which distinguish the epicuticular wax outside the plant cuticle
from the cuticular wax embedded in the cuticle polymer. These two are consequently now known to be chemically distinct, although the mechanism which segregates the molecular species into the two layers is unknown.
and reflect UV radiation. The shapes of the crystals are dependent on the wax compounds present in them. Asymmetrical secondary alcohols and β-diketones form hollow wax nanotubes
, while primary alcohol
s and symmetrical secondary alcohols form flat plates Although these have been observed using the transmission electron microscope and scanning electron microscope
http://www.blackwellpublishing.com/book.asp?ref=140513268X&site=1 the process of growth of the crystals had never been observed directly until Koch and coworkers studied growing wax crystals on leaves of snowdrop
(Galanthus nivalis) and other species using the atomic force microscope
. These studies show that the crystals grow by extension from their tips, raising interesting questions about the mechanism of transport of the molecules.
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
, the plant cuticle
Plant cuticle
Plant cuticles are a protective waxy covering produced only by the epidermal cells of leaves, young shoots and all other aerial plant organs without periderm...
is covered by epicuticular wax or bloom mainly consisting
of straight-chain aliphatic hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s with a variety of substituted groups, serving to decrease moisture loss and decay. Common
examples are paraffin
Paraffin
In chemistry, paraffin is a term that can be used synonymously with "alkane", indicating hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to a mixture of alkanes that falls within the 20 ≤ n ≤ 40 range; they are found in the solid state at room temperature and begin to enter the...
s in leaves of pea
Pea
A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...
s and cabbage
Cabbage
Cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae and is a leafy green vegetable...
s, alkyl ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s in leaves of carnauba palm and banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....
, the asymmetrical secondary alcohol 10-nonacosanol in most conifers such as Ginkgo biloba and Sitka spruce
Sitka Spruce
Picea sitchensis, the Sitka Spruce, is a large coniferous evergreen tree growing to 50–70 m tall, exceptionally to 95 m tall, and with a trunk diameter of up to 5 m, exceptionally to 6–7 m diameter...
, many of the Ranunculaceae
Ranunculaceae
Ranunculaceae are a family of about 1700 species of flowering plants in about 60 genera, distributed worldwide....
, Papaveraceae
Papaveraceae
Papaveraceae, informally known as the poppy family, are an economically important family of 44 genera and approximately 770 species of flowering plants in the order Ranunculales. The family is cosmopolitan, occurring in temperate and subtropical climates, but almost unknown in the tropics...
and Rosaceae
Rosaceae
Rosaceae are a medium-sized family of flowering plants, including about 2830 species in 95 genera. The name is derived from the type genus Rosa. Among the largest genera are Alchemilla , Sorbus , Crataegus , Cotoneaster , and Rubus...
and some mosses, symmetrical secondary alcohols in Brassicaceae
Brassicaceae
Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....
including Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
, primary alcohol
Primary alcohol
A primary alcohol is an alcohol which has the hydroxyl radical connected to a primary carbon. It can also be defined as a molecule containing a “–CH2OH” group.Examples include ethanol and butanol....
s (mostly octacosan-1-ol) in most grasses Poaceae
Poaceae
The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
, Eucalyptus
Eucalyptus
Eucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia...
and legumes among many other plant groups, β-diketone
Diketone
A diketone is a molecule containing two ketone groups. The simpliest diketone is diacetyl, also known as 2,3-butanedione. Diacetyl, acetylacetone, and hexane-2,5-dione are examples of 1,2-, 1,3-, and 1,4-diketones, respectively...
s in many grasses, Eucalyptus
Eucalyptus
Eucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia...
, box Buxus
Buxus
Buxus is a genus of about 70 species in the family Buxaceae. Common names include box or boxwood ....
and the Ericaceae
Ericaceae
The Ericaceae, commonly known as the heath or heather family, is a group of mostly calcifuge flowering plants. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th most speciose family of flowering plants...
, aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s in young beech
Beech
Beech is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America.-Habit:...
leaves, sugarcane
Sugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...
culms and lemon
Lemon
The lemon is both a small evergreen tree native to Asia, and the tree's ellipsoidal yellow fruit. The fruit is used for culinary and non-culinary purposes throughout the world – primarily for its juice, though the pulp and rind are also used, mainly in cooking and baking...
fruit and triterpene
Triterpene
Triterpenes are terpenes consisting of six isoprene units and have the molecular formula C30H48.The pentacyclic triterpenes can be classified into lupane, oleanane or ursane groups.Animal- and plant-derived triterpenes exist, such as:*squalene...
s in fruit waxes of apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
, plum
Plum
A plum or gage is a stone fruit tree in the genus Prunus, subgenus Prunus. The subgenus is distinguished from other subgenera in the shoots having a terminal bud and solitary side buds , the flowers in groups of one to five together on short stems, and the fruit having a groove running down one...
and grape
Grape
A grape is a non-climacteric fruit, specifically a berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or they can be used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, molasses and grape seed oil. Grapes are also...
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
and hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...
, making them accessible for chemical analysis, but in some species esterification of acids and alcohols into estolides or polymerization of aldehydes may give rise to insoluble compounds. Solvent extracts of cuticle waxes contain both epicuticular and cuticular waxes, often contaminated with cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
lipids of underlying cells. Epicuticular wax can now also be isolated by mechanical methods which distinguish the epicuticular wax outside the plant cuticle
Plant cuticle
Plant cuticles are a protective waxy covering produced only by the epidermal cells of leaves, young shoots and all other aerial plant organs without periderm...
from the cuticular wax embedded in the cuticle polymer. These two are consequently now known to be chemically distinct, although the mechanism which segregates the molecular species into the two layers is unknown.
Epicuticular wax crystals
Epicuticular wax forms crystalline projections from the plant surface, which enhance their water repellency, create a self-cleaning property known as the lotus effectLotus effect
The lotus effect refers to the very high water repellence exhibited by the leaves of the lotus flower ....
and reflect UV radiation. The shapes of the crystals are dependent on the wax compounds present in them. Asymmetrical secondary alcohols and β-diketones form hollow wax nanotubes
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
, while primary alcohol
Primary alcohol
A primary alcohol is an alcohol which has the hydroxyl radical connected to a primary carbon. It can also be defined as a molecule containing a “–CH2OH” group.Examples include ethanol and butanol....
s and symmetrical secondary alcohols form flat plates Although these have been observed using the transmission electron microscope and scanning electron microscope
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
http://www.blackwellpublishing.com/book.asp?ref=140513268X&site=1 the process of growth of the crystals had never been observed directly until Koch and coworkers studied growing wax crystals on leaves of snowdrop
Snowdrop
Galanthus is a small genus of about 20 species of bulbous herbaceous plants in the Amaryllis family, subfamily Amaryllidoideae...
(Galanthus nivalis) and other species using the atomic force microscope
Atomic force microscope
Atomic force microscopy or scanning force microscopy is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit...
. These studies show that the crystals grow by extension from their tips, raising interesting questions about the mechanism of transport of the molecules.