Biomedical Engineering Reference
In-Depth Information
Fig. 8.16 TEM transverse section through helicoidal cell wall in adaxial epidermis of an iridescent
green leaf ( a ) and an iridescent blue leaf ( b ) from D. tomentosu .( c ) TEM transverse section through
helicoidal cell wall in adaxial epidermis of an iridescent blue-green leaf from L. lucida .( d ) TEM
image of the iridisome in the fruits of D. michieana , showing an iridescent blue color. Scale bars:
( a )-( c )0.5 m; and ( d )2 m(( a )-( c ) Reproduced from [ 72 ]and( d ) from [ 75 ])
[ 74 , 75 ]. The multilayers are so-called “iridisomes” which are within the epidermal
cells. The molecular basis of iridosome is primarily cellulose, forming a layered
structure that can cause structural coloration via interference.
Structural coloration in plants may have some adaptive benefit, similar to
that in animals. Blue coloration in plant leaves may increase the capture of
photosynthetically important wavelengths, and may also be exploited as a visual
defence against herbivores or as a photoprotective mechanism to protect shade-
adapted plants against sun-flecks and other potentially damaging [ 70 ]. On the other
side, such structural coloration in fruits may aid in attracting mammals and large
frugivorous birds, and may also allow ripe fruits to continue photosynthetic carbon
assimilation [ 75 ].
In addition to simple periodic multilayers in the biological world, there also exist
modified multilayers. These modified multilayers include chirped [ 77 - 81 ], chiral
[ 10 , 71 - 73 , 82 - 92 ], and sculpted multilayers[ 93 - 96 ], which can produce interesting
structural coloration and may possess some intriguing selective advantages.
A periodic multilayer is a structure consisting of alternating layers of low- and
high-refractive indices (bilayers) with an identical bilayer thickness. In contrast,
the bilayer thickness in a chirped multilayer changes progressively with depth.
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