Seasonal changes in all major and minor photosynthetic pigments and
antioxidants were studied in sun and shade in beech
(Fagus sylvatica L.) leaves and buds under Mediterranean
conditions. Both sun and shade leaves differed progressively in their
biochemical and morphological characteristics during the course of leaf
ageing. Sun leaves were 3-fold thicker, pigment content was highly reduced and
the leaves were protected by a much more powerful antioxidative system.
Pigment content decreased progressively during summer in sun leaves and
remained stable in shade leaves. From July to September, there was no
chlorophyll (Chl) biosynthesis, so photodegradation of Chl was not compensated
by production of new Chl. This reduction in Chl occurred in parallel with an
increment in tocopherols. Natural leaf senescence occurred first in sun
leaves. During this process, Chl was completely degraded, xanthophylls were
esterified with fatty acids, and violaxanthin was converted into zeaxanthin,
while carotenes remained stable. One of the main indicators of tree decline
and air pollution is accelerated leaf ageing, and this process is
characterised in beech leaves by tocopherol and pigment destruction, so we
have used these criteria to verify whether these parameters can be used as
early indicators of tree decline. All pigments and antioxidants (including
α -tocopherol) decreased with beech decline, except xanthophyll cycle
pigments. As reduction of these compounds is concomitant with a similar level
of Chl degradation, Chl determination is proposed as a simple method
sufficient to predict the early stages of beech decline at a biochemical
level.
Photosynthetic induction and activity of enzymes related to carbon metabolism: insights into the varying net photosynthesis rates of coffee sun and shade leaves
