The structure and development of stomata
by Willmer C. M., Fricker M. (1996)
- University of Stirling, UK
in In: Stomata. Springer, Dordrecht 36-91 – https://doi.org/10.1007/978-94-011-0579-8_3 –
The epidermis is the outermost cell layer or layers of the leaf lamina and serves to protect against excessive and uncontrolled water loss from the leaf It also acts as a physical barrier, reducing infection by fungal pathogens and bacteria, and minimizes mechanical damage to the mesophyll tissue.
The epidermal tissue is not normally photosynthetic, but can significantly affect the radiation received by the underlying tissues. Wax secretion (e.g. Mulroy, 1979) and epidermal structures, such as trichomes and salt glands (e.g. Mooney et al., 1977), can result in large changes in leaf spectral characteristics, such as increased leaf reflectance, particularly of UV wavelengths.
The epidermis is also the major site of absorption of UV radiation due mainly to a range of differ- ent flavenoid and phenolic pigments which are contained in the cells (Robberecht and Caldwell, 1978; Robberecht et al., 1980) and waxes on the surface of the epidermis. Figure 3.1 shows the absorption spectra of ethanol extracts of epidermal and mesophyll tissues from Commelina and illustrates the high UV absorption of the former tissue relative to the latter.
In many cases the upper and lower epidermes do not have the same spectral characteristics, with higher UV absorbance from the adaxial surface (Donkin and Martin, 1981; Weissenbock et al., 1986; Shimazaki et al., 1988).
The epidermis attenuates transmission of photosynthetically active radiation (PAR) to a small degree, although scattering and reflection from the abaxial epidermis also prevents the light from escaping once it has entered the leaf (Lin and Ehleringer, 1983).