19 research outputs found
The ability of abaxial and adaxial epidermis of sun and shade leaves to attenuate UV-A and UV-B radiation in relation to the UV absorbing capacity of the whole leaf methanolic extracts
The UV-absorbing capacity (measured as A(310) cm(-2) and A(365) cm(-2) or AUVR cm(-2)) of the shade leaves of four representative evergreen sclerophylls of the Mediterranean region (Quercus coccifera, Q. ilex, Arbutus andrachne and A. unedo) was considerably lower than the corresponding one of sun leaves of the same species. However, fibre optic microprobe measurements showed that adaxial as well as abaxial epidermis of shade leaves of all examined plants, except abaxial epidermis of A. andrachne, were almost as effective as the corresponding ones of the sun leaves in screening out most of the incident UV-B radiation. There is probably a threshold, under which the concentration of the UV-B absorbing compounds in the protective tissues is not furthermore reduced, in spite of the low levels of the stress factor (UV-B radiation) in the environment. On the other hand, the ability of both abaxial and adaxial epidermis to attenuate UV-A radiation, except of adaxial leaf epidermis of Quercus species, depended on the UV absorbing capacity of the whole-leaf extracts, with different correlation patterns between the two Quercus species and the two Arbutus species. This could be explained by the fact that shade leaves showed not only quantitative, but also qualitative differences (higher A(310)/A(365) ratio) in the absorbance of their methanolic extracts compared to these of sun leaves. The results of the present study showed that we should not always correlate the depth of penetration of UV radiation into sun and shade leaves according to the corresponding UV absorbing capacity of the whole leaf methanolic extracts, without taking into account all the anatomical, developmental and biochemical (such as different composition and distribution of the UV-absorbing compounds among the different protective tissues) peculiarities of the leaves of each species
Seasonal fluctuations in the concentration of UV-absorbing compounds in the leaves of some Mediterranean plants under field conditions
Leaves of 14 representative Mediterranean plant species were collected
on a monthly basis and assayed for UV-absorbing compounds concentration,
either on an area or a dry mass basis, from 1995 to 1997, Strong
seasonal fluctuations were observed in eight species tall evergreens,
two phrygana, one deciduous, one summer perennial and one winter
perennial). Two different patterns of changing concentrations of
UV-absorbing compounds were observed. In the first, concentration of
these compounds was higher in young developing leaves and concentration
declined during maturation, whereas in other plants, the opposite trend
was observed. These differences could be attributed to the particular
leaf surface morphology of each plant. The observed seasonal
fluctuations of UV-absorbing compounds seem to be more correlated to
developmental processes, than to seasonal fluctuations of the naturally
occurring UV-B radiation. Most of the winter perennials did not show
strong fluctuations during the period of development. The concentration
of these compounds varied not only on a seasonal basis among the
examined plants, but between different life forms as well: during
winter, examination of the leaves of 13 species showed that evergreen
sclerophylls and phrygana had at least two-fold higher concentration of
UV-B-absorbing compounds on a leaf area basis than winter perennials. In
addition, during the same season and irrespective of life form and
species, the absorbance at 300 nm per unit of mature leaf area followed
an asymptotic exponential decrease when specific leaf area increased.
The UV-B radiation screening capacity of the leaves of these plants is
discussed in relation to each adaptive strategy
Structural analysis of Castanea sativa Mill. leaves from different regions in the tree top
The aim of this work was to perform the histological characterization of the C. sativa leaves of three Portuguese cultivars to establish comparison among the leaves of the different quadrants in accord and with the cardinal points of the tree top and among different cultivars of this species, using light microscopy (OM) and scanning electron microscopy (SEM). Measurements were also carried out for the leaf tissue thickness, stomatal density, leaf area in the four tree top quadrants. The leaves turned to the North had lesser thickness of mesophyll mainly due to lower amount of palisade parenchyma. The stomatal density was significantly lower in these leaves, unlike the leaf area that has the highest expression