Plant cuticle
The cuticle of plants is a waxy coating which is formed only in epidermal cells of leaves, young shoots and other tissues exposed to the air without periderm. Due to their hydrophobic properties, it reduces water losses; in plants in dry areas to 0.01 % of what would make an equal and free water surface. At locations which, however, the exchange is required, the cuticle may also be porous or cracked. The rhizodermis has even no cuticle so as not to impede water and nutrient uptake.
Chemical constituents
The cuticle consists of an insoluble cuticular membrane impregnated with and covered with soluble waxes. Cutin is the most well known, structural components of the cuticular membrane. The cuticle may also include a non- saponifiable hydrocarbon called Cutan. The epicuticular waxes, which cover the cuticle, composed of a mixture of hydrophobic, aliphatic compounds of hydrocarbons having a chain length of 16 to 36, the cutin is synthesized as a monomer in the epidermis, and then crosslinked in the cuticle. The same applies to the wakefulness and deposits, but the diffuse easily in and through the cuticle. To this end, they will probably dissolved in short-chain hydrocarbons that evaporate at destination. But it is also involved lipid transfer proteins.
Structure and Function
The plant cuticle can follow growth, in contrast to insects, which have to molt. This is because cross-linking of Cutinmatrix then further monomers can be incorporated and dissolved by Cutinases. When the cuticle is growing faster than the epidermis, it comes to Cuticularfältelung. This leads to a poorer wettability, water droplets, due to the surface tension touching only the tips of the Cuticularfalten and stick so bad. So is the cuticle and the defense, because when it rains virus particles, bacterial cells and spores or growing Pilzfilamenten be washed off. In plants at very dry sites can be found also very thick cuticles. These are difficult to chemically and mechanically vulnerable and also withstand Kauwerkzeugen of smaller animals.
On the cuticle epicuticuläre waxes can be stored additionally. These crystalloids can take numerous forms, as needles, plates or packets, arranged seemingly randomly or in planned manner, etc. Strong wax precipitates can already be seen with the naked eye; they look like ripe, such as plums or cabbage leaves. Wax coatings reduce transpiration more, reflect, or scatter incident light, to increase air turbulence over the surface, so that the heat exchange is increased and lower the wettability, as well as the Cuticularfalten. The latter is particularly pronounced at the lotus flower (Nelumbo nucifera ), so named after her as lotus effect is the effect (described by Barthlott and Neinhuis, 1997). Thickness of coats of wax as well as a thick cuticle protect against corrosion, as the mandibles and tarsi of the animals are bonded.
While it is at the cuticle to a Akkrustierung ( Auflagerung ), it can also lead to incrustations ( retention ) of suberin or cutin. Thus, the cell walls can not only water, but in the case of cork also be impermeable to air ( impressively demonstrated on the champagne corks ). It can be incorporated into the cell wall and inorganic substances such as calcium carbonate and calcium oxalate in Schirmalge Acetabularia. Silica can be found in grasses and diatoms (Diatoms ). The cell wall, embedding indeed harder, but also more brittle ( inelastic ).
Evolution
The cuticle was more than 450 million years ago during the transition of plants from water to land along with stomata, xylem, phloem and intercellular spaces in the mesophyll tissue in the root first, and later in the Gazette. A combination of these innovations enabled the plants by the relocation of gas exchange to reduce the loss of water into the interior. Enclosed by a waterproof membrane, and openings defined by the variable width of the stomata can control perspiration and CO exchange.