However, an increasing number of publications report the discovery of new wax components and a long list of rare and uncommon ingredients, such as methyl-branched aliphatics [29].
For some wax components, derivatization is required; as fatty acids and fatty alcohols are not volatile, derivatization is necessary [10] but fatty hydrocarbons are volatile and can be analyzed without derivatization [11].
It might be, therefore, that MAH1-derived wax components in barley are less important against pathogen attack as structural barriers but instead act in signaling.
Wax components such as hexacosanol, octacosanol, and hexacosanoic acid were also found at diminished levels in conspecific versus heterospecific stands (Table 3).
Presence of either the Iw1 or Iw2 allele greatly reduces ß-diketones in the wax components of plants, resulting in a non-glaucous phenotype [ 3, 10].
Clade 9 includes 21 transporters similar to AT1G17840.1 and AT1G51500.1, which are required for export of wax components such as alkanes [ 57].
In Arabidopsis the main epicuticular wax components are alkanes, secondary alcohols and ketones with a chain length of C29, all of which are synthesized via a MAH1-dependent pathway [ 36].
Considering that trichome contained a multitude of wax components and can secrete lipids [ 66], the lack of trichome may save total energy and resources for lipid biosynthesis in other organs such as seeds and leaves of transgenic plants.
But little is known about this 'protective barrier' (Shepherd and Griffiths 2006) in horsetails, whose EW layer should provide protection against abiotic stresses related to temperature, light and pollution: the only reported wax components in Equisetum are fatty acids with chain lengths between C22 and C30 (Řezanka 1998).
Therefore, all excavated wall painting specimens should have been preserved from potential deterioration caused by the subsequent eruption of Vesuvius in 79 A.D. In addition, based on our results, these samples did not contain waxes, components often used in the past for maintenance works carried out to restore the original painting colors [22],[22].
