In
botanyBotany, plant science, phytology, or plant biology is a branch of biology and is the scientific study of plant life and development...
, the
plant cuticlePlant 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 mainly consisting
of straight-chain aliphatic
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon and hydrogen are referred to as "pure"...
s with a variety of substituted groups. Common
examples are
paraffinIn chemistry, paraffin is the common name for the alkane hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to the solids with 20 ≤ n ≤ 40 ....
s in leaves of
peaA pea is most commonly the small spherical seed or the seed-pod of the legume Pisum sativum. Each pod contains several peas. Although it is botanically a fruit, it is treated as a vegetable in cooking...
s and
cabbageThe cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae , and is used as a leafy green vegetable...
s, alkyl
esterEsters 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
bananaBanana is the common name for a herbaceous plants of the genus Musa, and the commonly eaten fruit it produces. They are native to the tropical region of Southeast Asia, and are likely to have been first domesticated in Papua New Guinea. Today, they are cultivated throughout the tropics.Banana...
, the asymmetrical secondary alcohol 10-nonacosanol in most conifers such as
Ginkgo biloba and
Sitka spruceThe Sitka Spruce is a large coniferous evergreen tree growing to 50–70 m tall, exceptionally to 100 m tall, and with a trunk diameter of up to 5 m, exceptionally to 6–7 m diameter. It is by far the largest species of spruce, and the third tallest conifer species in the world...
, many of the
RanunculaceaeRanunculaceae is a family of flowering plants also known as the "buttercup family" or "crowfoot family". The family name is derived from the genus Ranunculus. Members include Anemone , Ranunculus , Aconitum , and Clematis...
,
PapaveraceaePapaveraceae is a family of flowering plants. The family has been universally recognized by taxonomists, and is also known as the "poppy family". It is a cosmopolitan family occurring in temperate and subtropical climates. Most are herbaceous plants, but a few are shrubs and small trees.The plants...
and
RosaceaeThe Rosaceae or rose family is a large family of plants, with about 3000 species in 100 genera . The name is derived from the genus Rosa...
and some mosses, symmetrical secondary alcohols in
BrassicaceaeBrassicaceae or Cruciferae, also known as the crucifers, the mustard family or cabbage family is a family of flowering plants . The name Brassicaceae is derived from the included genus Brassica. Cruciferae is an older name, meaning "cross-bearing", because the four petals of their flowers are...
including
Arabidopsis thalianaArabidopsis 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 alcoholA 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
PoaceaePoaceae or Gramineae is a family in the Class Liliopsida of the flowering plants. Plants of this family are usually called grasses, or, to distinguish them from other graminoids, true grasses; the shrub- or tree-like plants in this family are called bamboo...
,
EucalyptusEucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia. There are more than 700 species of Eucalyptus, mostly native to Australia, and a very small number are found in adjacent parts of New Guinea and Indonesia...
and
legumeIn botanical writing legume is a plant in the family Fabaceae , or a fruit of these specific plants. A'legume' fruit is a simple dry fruit that develops from a simple carpel and usually dehisces on two sides. A common name for this type of fruit is a pod, although "pod" is also applied to a few...
s among many other plant groups, β-
diketoneA 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,
EucalyptusEucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia. There are more than 700 species of Eucalyptus, mostly native to Australia, and a very small number are found in adjacent parts of New Guinea and Indonesia...
, box
BuxusBuxus is a genus of about 70 species in the family Buxaceae. Common names include box or boxwood ....
and the
EricaceaeEricaceae, the heath family or the heather family is a plant family, comprising mostly calcifuge plants that thrive in acidic soils. Many well-known plants of the Ericaceae live in temperate climates, such as cranberry, blueberry, various heaths and heathers , huckleberry, azalea and rhododendron...
,
aldehydeAn aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double-bonded to an oxygen atom , is called the aldehyde group...
s in young
beechBeech is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America.The leaves of beech trees are entire or sparsely toothed, from 5–15 cm long and 4–10 cm broad...
leaves,
sugarcaneSugarcane, or sugar cane, is any of six to thirty-seven species of tall perennial grasses of the genus Saccharum . Native to warm temperate to tropical regions of Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six meters tall...
culms and [lemon] fruit and
triterpeneTriterpene is one of a class of compounds having molecular skeletons containing 30 carbon atoms, and theoretically composed of six isoprene units; numerous and widely distributed in nature, occurring principally in plant resins and sap; an example is ambrein....
s in fruit waxes of
appleThe apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family Rosaceae. It is one of the most widely cultivated tree fruits...
,
plumA 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 the side buds solitary , the flowers being grouped 1-5 together on short stems, and the fruit having a groove running down one side,...
and
grapeA grape is the non-climacteric fruit, botanically a true berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, and grape seed oil...
These compounds are mostly soluble in organic solvents such as
chloroformChloroform is the organic compound with formula CHCl
3. This colourless, sweet-smelling, dense liquid is a trihalomethane. It is also considered somewhat hazardous...
and
hexaneHexane is an alkane hydrocarbon with the chemical formula CH34CH3 or C6H14. The "hex" prefix refers to its six carbons, while the "ane" ending indicates that its carbons are connected by single bonds...
, 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.
In
botanyBotany, plant science, phytology, or plant biology is a branch of biology and is the scientific study of plant life and development...
, the
plant cuticlePlant 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 mainly consisting
of straight-chain aliphatic
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon and hydrogen are referred to as "pure"...
s with a variety of substituted groups. Common
examples are
paraffinIn chemistry, paraffin is the common name for the alkane hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to the solids with 20 ≤ n ≤ 40 ....
s in leaves of
peaA pea is most commonly the small spherical seed or the seed-pod of the legume Pisum sativum. Each pod contains several peas. Although it is botanically a fruit, it is treated as a vegetable in cooking...
s and
cabbageThe cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae , and is used as a leafy green vegetable...
s, alkyl
esterEsters 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
bananaBanana is the common name for a herbaceous plants of the genus Musa, and the commonly eaten fruit it produces. They are native to the tropical region of Southeast Asia, and are likely to have been first domesticated in Papua New Guinea. Today, they are cultivated throughout the tropics.Banana...
, the asymmetrical secondary alcohol 10-nonacosanol in most conifers such as
Ginkgo biloba and
Sitka spruceThe Sitka Spruce is a large coniferous evergreen tree growing to 50–70 m tall, exceptionally to 100 m tall, and with a trunk diameter of up to 5 m, exceptionally to 6–7 m diameter. It is by far the largest species of spruce, and the third tallest conifer species in the world...
, many of the
RanunculaceaeRanunculaceae is a family of flowering plants also known as the "buttercup family" or "crowfoot family". The family name is derived from the genus Ranunculus. Members include Anemone , Ranunculus , Aconitum , and Clematis...
,
PapaveraceaePapaveraceae is a family of flowering plants. The family has been universally recognized by taxonomists, and is also known as the "poppy family". It is a cosmopolitan family occurring in temperate and subtropical climates. Most are herbaceous plants, but a few are shrubs and small trees.The plants...
and
RosaceaeThe Rosaceae or rose family is a large family of plants, with about 3000 species in 100 genera . The name is derived from the genus Rosa...
and some mosses, symmetrical secondary alcohols in
BrassicaceaeBrassicaceae or Cruciferae, also known as the crucifers, the mustard family or cabbage family is a family of flowering plants . The name Brassicaceae is derived from the included genus Brassica. Cruciferae is an older name, meaning "cross-bearing", because the four petals of their flowers are...
including
Arabidopsis thalianaArabidopsis 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 alcoholA 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
PoaceaePoaceae or Gramineae is a family in the Class Liliopsida of the flowering plants. Plants of this family are usually called grasses, or, to distinguish them from other graminoids, true grasses; the shrub- or tree-like plants in this family are called bamboo...
,
EucalyptusEucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia. There are more than 700 species of Eucalyptus, mostly native to Australia, and a very small number are found in adjacent parts of New Guinea and Indonesia...
and
legumeIn botanical writing legume is a plant in the family Fabaceae , or a fruit of these specific plants. A'legume' fruit is a simple dry fruit that develops from a simple carpel and usually dehisces on two sides. A common name for this type of fruit is a pod, although "pod" is also applied to a few...
s among many other plant groups, β-
diketoneA 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,
EucalyptusEucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia. There are more than 700 species of Eucalyptus, mostly native to Australia, and a very small number are found in adjacent parts of New Guinea and Indonesia...
, box
BuxusBuxus is a genus of about 70 species in the family Buxaceae. Common names include box or boxwood ....
and the
EricaceaeEricaceae, the heath family or the heather family is a plant family, comprising mostly calcifuge plants that thrive in acidic soils. Many well-known plants of the Ericaceae live in temperate climates, such as cranberry, blueberry, various heaths and heathers , huckleberry, azalea and rhododendron...
,
aldehydeAn aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double-bonded to an oxygen atom , is called the aldehyde group...
s in young
beechBeech is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America.The leaves of beech trees are entire or sparsely toothed, from 5–15 cm long and 4–10 cm broad...
leaves,
sugarcaneSugarcane, or sugar cane, is any of six to thirty-seven species of tall perennial grasses of the genus Saccharum . Native to warm temperate to tropical regions of Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six meters tall...
culms and [lemon] fruit and
triterpeneTriterpene is one of a class of compounds having molecular skeletons containing 30 carbon atoms, and theoretically composed of six isoprene units; numerous and widely distributed in nature, occurring principally in plant resins and sap; an example is ambrein....
s in fruit waxes of
appleThe apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family Rosaceae. It is one of the most widely cultivated tree fruits...
,
plumA 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 the side buds solitary , the flowers being grouped 1-5 together on short stems, and the fruit having a groove running down one side,...
and
grapeA grape is the non-climacteric fruit, botanically a true berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, and grape seed oil...
These compounds are mostly soluble in organic solvents such as
chloroformChloroform is the organic compound with formula CHCl
3. This colourless, sweet-smelling, dense liquid is a trihalomethane. It is also considered somewhat hazardous...
and
hexaneHexane is an alkane hydrocarbon with the chemical formula CH34CH3 or C6H14. The "hex" prefix refers to its six carbons, while the "ane" ending indicates that its carbons are connected by single bonds...
, 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 membraneThe cell membrane is the biological membrane separating the interior of a cell from the outside environment....
lipids of underlying cells. Epicuticular wax can now also be isolated by mechanical methods which distinguish the epicuticular wax outside the
plant cuticlePlant 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 effectThe Lotus effect refers to the very high water repellency 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, while
primary alcoholA 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 microscopeThe scanning electron microscope is a type of electron microscope that images the sample surface 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
snowdropGalanthus is a small genus of about 20 species in the family Amaryllidaceae commonly known as Snowdrops. They are among the first bulbs to bloom in spring, although certain species flower in late autumn and winter....
(
Galanthus nivalis) and other species using the
atomic force microscopeThe atomic force microscope or scanning force microscope is a very high-resolution type of scanning probe microscopy, with demonstrated resolution 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.