258 research outputs found
Resurrection plants: The puzzle of surviving extreme vegetative desiccation
No full textTolerance to near complete desiccation of vegetative organs is a widespread capability in bryophytes and is also shared by a small group of vascular plants known as resurrection plants. To date more than 300 species, belonging to pteridophytes and angiosperms, have been identified that possess this kind of desiccation-tolerance. The vegetative desiccation-tolerance of resurrection plants is an inductive process displayed only under environmental stress with or without the involvement of abscisic acid as molecular signal. The different problems associated with desiccation encountered by resurrection plants render the employment of many interacting mechanisms necessary. Preservation of cell order and correct structure of membranes and macromolecules is underpinned by the synthesis of large amounts of sugars, amino acids, and small polypeptides such as late embryogenesis abundant (LEA) proteins and dehydrins. Some of these compatible solutes, such as sucrose and LEA proteins, are also involved in cytoplasm vitrification, which occurs during the last phase of desiccation. Mechanical damage due to vacuole shrinkage in dehydrating cells is avoided by cell wall folding or by replacing the water in vacuoles with nonaqueous substances. Oxidative stress, due to enhanced production of reactive oxygen species (ROS) especially by chloroplasts, is minimized through two different strategies. The homoiochlorophyllous resurrection plants, which conserve chloroplasts with chlorophylls and thylakoids upon drying, fold leaf blades and synthesize anthocyanins, as both sunscreens and free radical scavengers, and additionally increase the activity of antioxidant systems in cells. In contrast, the chloroplasts in poikilochlorophyllous species degrade chlorophylls and thylakoid membranes yielding desiccoplasts that are devoid of any internal structures. These adaptive mechanisms preserve cells from damage by desiccation and allow them to resume vital functions once rehydrated. Even if based mainly on cell protection during drying, the vegetative desiccation-tolerance of resurrection plants also relies on systems of cell recovery and repair upon rehydration. However, most of these systems are prepared during cell dehydration
Variegation in Arum italicum leaves. A structural–functional study
No full textThe presence of pale-green flecks on leaves (speckling) is a frequent character among herbaceous species from shady places and is usually due to local loosening of palisade tissue (air space type of variegation). In the winter-green Arum italicum L. (Araceae), dark-green areas of variegated leaf blades are ca. 400 mu m thick with a chlorophyll content of 1080 mg m(-2) and a palisade parenchyma consisting of a double layer of oblong cells. Pale-green areas are 25% thinner, have 26% less chlorophyll and contain a single, loose layer of short palisade cells. Full-green leaves generally present only one compact layer of cylindrical palisade cells and the same pigment content as dark-green sectors, but the leaf blade is 13% thinner. A spongy parenchyma with extensive air space is present in all leaf types. Green cells of all tissues have normal chloroplasts. Assays of photosynthetic activities by chlorophyll fluorescence imaging and 02 exchange measurements showed that variegated pale-green and dark-green sectors as well as full-green leaves have comparable photosynthetic activities on a leaf area basis at saturating illumination. However, full-green leaves require a higher saturating light with respect to variegated sectors, and pale-green sectors support relatively higher photosynthesis rates on a chlorophyll basis. We conclude that i) variegation in this species depends on number and organization of palisade cell layers and can be defined as a "variable palisade" type, and ii) the variegated habit has no limiting effects on the photosynthetic energy budget of A. italicum, consistent with the presence of variegated plants side by side to full-green ones in natural populations. (C) 2011 Elsevier Masson SAS. All rights reserved
La "nuova" difesa d'ufficio. Aspetti pratico - operativi
No full textIl lavoro descrive l'istituto della difesa d'ufficio nelle varie fasi procedimenti e processuali in cui può essere richiesto l'intervento tecnico di un avvocato che non sia di fiduci
Chloroplast signals regulating nuclear gene expression: Past hypothesis and present knowledge
No full textIdentification and characterization of D1 and D2 protein breakdown fragments in cotyledon thylakoids from Ceratonia siliqua L.
No full textBreakdown products of Photosystem II reaction centre D1 and D2 proteins have been detected and
characterized in cotyledon thylakoids from the epigeal species Ceratonia siliqua. Breakdown fragments
are mainly localized in the stroma-exposed membranes. Cleavage of D1 protein occurs in the hydrophylie
loop connecting the 4th and 5th putative transmembrane segments, giving rise to fragments very similar,
if not identical, to those observed during light-induced turnover or photoinhibition. Fragments
from D2 protein originate from cleavage somewhere between the 3rd and 4th transmembrane segments
Variegation in Erythronium dens-canis L. (Liliaceae) leaves: a structural functional study.
No full textTrade-offs between leaf hydraulic capacity and drought vulnerability: morpho-anatomical bases, carbon costs and ecological consequences
No full textErythronium dens-canis L. (Liliaceae): An unusual case of change of leaf mottling
No full textErythronium dens-canis is an early-flowering understory lily of southern Europe with two leaves and a
single flower, although a number of plants have only one leaf and do not flower. The leaves are mottled
with silvery flecks and brown patches, that gradually vanish turning to a lively green color. The nature
and function of this striking variegation pattern were investigated in differently colored leaf parts
following the springtime color change. Tissue organization was examined by light and electron microscopy;
photosynthetic pigments were analyzed by spectrophotometry and HPLC; chlorophyll fluorescence
parameters were evaluated by MINI-PAM. The results showed that brown patches originated in
vacuolar anthocyanins in the subepidermal cell layer while air spaces between the upper epidermis and
underlying chlorenchyma resulted in silvery flecks. The two leaf areas did not differ in photosynthetic
pigments, chloroplast organization and photosynthetic parameters (Fv/Fm, NPQ, rETR). Greening of brown
patches due to anthocyanin resorption was faster in non-flowering plants than in flowering ones,
occurring only when young fruits were developing. Anthocyanin disappearance did not change the
structural-functional features of photosynthetic tissues. As a whole the results suggest that the anthocyanin
pigmentation of E. dens-canis leaves does not affect the photosynthetic light use and has no
photoprotective function. It is proposed that the complex leaf color pattern may act as a camouflage to
escape herbivores, while the reflective silvery spots may have a role in attracting pollinators of this earlyflowering
species
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