Occurrence of tannins in leaves of beech trees (Fagus sylvatica) along an ecological gradient, detected by histochemical and ultrastructural analyses

Abstract

Sclerophylly and synthesis of phenolic compounds are active responses of plants subjected to environmental stress (drought, low nutrient supply, u.v.-B radiation, ozone). Here we describe the morphological and histochemical alterations occurring in field-grown leaves of Fagus sylvatica L. from three sites located along an ecological gradient : from a site in cool and protected conditions to one located on a mountain ridge, where the trees grow on a thin layer of soil and are exposed to the wind and to intense solar radiation in summer. The morphological data show that, as the ecological conditions of the stand worsen, individual leaf surface decreases, while the thickness of the leaves and their specific d. wt (i.e. d. wt per unit leaf area) increases. Histochemical and ultrastructural tests show a marked increase of phenolics during the course of the year. These substances, present primarily in the leaves of trees growing in stress conditions, have been identified mainly as tannins. They accumulate in the vacuoles, especially those of the upper epidermal layer and the palisade mesophyll ; at a later stage they appear to be solubilized in the cytoplasm and retranslocated, eventually impregnating the outer wall of the epidermal cells amidst the cellulose fibrils, where they cluster together and form an electron-opaque layer between the wall and the cuticle. Observation of the epidermal cells also reveals that the outer cell wall is thicker. The paper discusses the roles of secondary metabolites in protection and detoxification processes ; the possible ecological significance of these alterations in the ecophysiology of beech trees.

The influence of microclimate and tree age on the defense capacity of European beech (Fagus sylvatica L.) against oxidative stress

“…Throughout the growing season, the seedlings were watered regularly in order to avoid drought stress. Although the leaves studied differed significantly with respect to specific leaf area (table I), the values were within the range found in previous studies for sun and shade exposed leaves of adult canopy trees [5,12,20] and seedlings [2,26,41].…”

Tropospheric ozone-induced structural changes in leaf mesophyll cell walls in grapevine plants

“…We interpret these changes as an indication of the sensitivity of Vitis vinifera to tropospheric ozone which resulted in morphological response. This is in accordance with previous studies, in which O 3 sensitivity has been correlated with leaf thickening (Crang & McQuattie, 1986;Bennett et al, 1992;Pääkkönen et al, 1995;Bussotti et al, 1998;Oksanen et al, 2001).…”

Anatomia de folha e caule e quantificação espectrofotométrica de fenóis totais e taninos da erva-de-bicho (Polygonum acre Kunth var. aquatile Meisn.)

“…Como as plantas, que apesar de imóveis são organismos dinâmicos, o esperado é que o acúmulo de polifenóis varie ao longo das estações do ano, pois o conteúdo polifenólico é dependente de fatores intrínsecos (genéticos) e extrínsecos -ambientais (Fratianni et al 2007) variando diante de diversas situações, como o tipo de órgão da planta (Falleh et al 2008), fase do desenvolvimento vegetal (Schweitzer et al 2008), local de cultivo ou ocorrência e entre as diferentes estações do ano (Bussotti et al 1998, Ma et al 2003, Brooks & Feeny 2004. As variações do conteúdo polifenólico são definidas por base genética que é fortemente afetada pelas condições seja do ambiente .…”