F. Dalla Vecchia

Two Different Endo-β-1,4-Glucanases Contribute to the Softening of the Strawberry Fruits

Summary The expression of different endo-(β-l,4-glucanases (EGases) and the ultrastructural details of the cell wall dismantling were studied throughout the development of the strawberry fruits. Detectable enzyme activity is first observed in large green fruits, but a steep increase occurs in white fruits when the ripening process proper starts. This process is then accompanied by a further increase in EGase activity which appears to be doubled in red ripe fruits. Two isoforms with different isoelectric points (pI 7.9 and 9.0, respectively) contribute to the observed enzyme activity, and both isoenzymes increase in activity as fruits ripen. Two cDNA fragments, encoding two divergent endo-(β-l,4-glucanases (faEGlO and faEG30, respectively), were obtained by RT-PCR and the expression of their related mRNAs examined by northern analysis. faEG30-related transcripts start to be detected in large green fruits, while faEGlO expression is detected in white fruits. Thereafter, the amount of both EGase mRNAs increases throughout the ripening process up to the stage of red ripe fruits. The fine structure of the cell wall weakening which occurs during the ripening is well in accordance with the above described biochemical and molecular data.

Effects of Amitrole and Norflurazon on Carotenogenesis in Barley Plants Grown at Different Temperatures

A carotenoid deficiency can account for serious alterations of thylakoids, due to the essential roles played by these pigments in membrane protection against photo-oxidative damage (1,2). In spite of carotenoid importance in preserving the photosynthetic apparatus, information on their biosynthesis in green tissues is rather scarce, and the knowledge of carotenogenesis and its regulation mainly comes from studies on chromoplasts of ripening fruits (3,.4). Previous research on the lycopinic tigrina o 34 mutant of barley (5) and on barley plants treated with amitrole (6), a herbicide inhibiting lycopene cyclization (7), showed that plant growth temperature could affect carotenoid biosynthesis in leaf chloroplasts, suggesting the existence of thermo-modulated steps bypassing the block of mutation or herbicide. Recently, in tomato (4) and Arabidopsis (8) alternative reactions, which allow s-carotene and xanthophylls to be synthesized without involving lycopene as intermediate, have been proposed. In order to better define the relationship between temperature and carotenoid synthesis in chloroplasts, barley plants have been grown at two rather close temperatures. They have been treated with two herbicides, to analyze whether interruption of the carotenogenic pathway at distinct points would cause differentiated responses to the change in plant growth temperature. The two chemicals used were norflurazon (NF) and amitrole (AM), which inhibit phytoene desaturation and lycopene cyclization, respectively (7). In leaves of plants grown in different experimental conditions, the total and relative quantities of carotenoids synthesized and the ratios between the pigment forms were analyzed. The ultrastructural organization, chlorophyll contents and photosynthetic activity of chloroplasts were also investigated, to verify the photooxidative damage caused by the disturbed carotenoid biosynthesis.

Some observations on phycobilisomes of Pterocladiella capillacea (Gelidiaceae, Rhodophyta)

ABSTRACT Phycobilisomes (PBSs) of the red alga Pterocladiella capillacea collected in the field, were characterized both in situ and in vitro by means of a transmission electron microscope (TEM) and an image analyzer. Ultrathin sections of thalli and negatively stained PBSs after isolation revealed hemi-ellipsoidal shapes. In situ PBS dimensions were 38.5 ± 0.2 nm (height) × 38.8 ± 0.2 nm (width) × 22.6 ± 0.2 nm (thickness) in good agreement with the in vitro measurements (mean diameters of 37.6 ± 0.2 nm). These dimensions, especially the width, are smaller than those so far reported for red algae. This could depend either on the ecophysiological conditions of the thalli when harvested and/or on a staggered, symmetrically rotated and compressed disposition of biliprotein rods with respect to the allophycocyanin (APC) core. Hydroxylapatite chromatography of biliproteic extracts and SDS-PAGE electrophoresis revealed that phycoerythrin type R-(λmax 565 nm>540 nm>498 nm) is formed by α (18.6 kDa), β (19.9 kDa...

Early seedling growth and morphogenesis in the xantha1 mutant of sunflower with alteration of chloroplast biogenesis

In the xantha1 (xan1) mutant of sunflower (Helianthus annuus L.), the effects on organ anatomy and seedling growth did correlate to the alteration of chloroplast biogenesis. The xan1 seedlings grown under 165 µmol(photon) m−2 s−1 revealed a severely altered chloroplast ultrastructure in cotyledons and leaves. Cross-sections or clarified tissues of the xan1 cotyledons did not show evident alterations with respect to normal cotyledons suggesting that the impairment of chloroplast biogenesis has negligible consequences on embryonic leaves. By contrast, the analysis of xan1 leaves showed that the defects in chloroplast biogenesis were correlated to a drastic reduction of organ size and to a clear enhancement of the trichome growth. The differentiation of palisade and spongy parenchyma in cotyledons and leaves of the xan1 mutant was normal but both organs displayed a drastic reduction in the plastid number with respect to wild type. In addition, xan1 hypocotyls showed a reduced development of the main vascular bundles in comparison with normal seedlings and an undersized central cylinder of the primary root. The exogenous supply of sucrose was not sufficient to revert in vitro the deficit of xan1 growth and the constraints in morphogenetic processes.

Developmental and Photosynthetic Characteristics of a Photoautotrophic Chrysanthemum Culture

Chrysanthemum plantlets were cultivated in vitro on media with 2.0, 0.3, or 0 % sucrose, or photoautotrophically without an organic carbon source but with supplementation of the culture vessel atmosphere with 2 % CO2. The photoautotrophically cultivated plantlets showed a better growth and multiplication, higher contents of chlorophyll (Chl) and carotenoids, higher Chl a/b ratio, net photosynthetic rate and ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase activities than plantlets grown on the medium with sucrose.

Morphological and phytochemical aspects of three alien Opuntia species on Euganean Hills in North-Eastern Italy

In this study, Opuntia stricta, O. engelmannii, and O. humifusa, naturalized alien units in the Euganean Hills (North-Eastern Italy), are investigated. Different morphological and physiological features both in cladodes collected in summer and winter and in fruits arisen from two blooms are reported. The morphological observations showed a different organization in epidermis/hypodermis of cladodes collected in winter and in summer, probably correlated to the individual plant reaction to a stressful factor as low temperature. Scanning electron microscopy observations revealed no differences in the deposition of waxes and stomata distribution in the epidermis of cladodes. The betacyanin analysis showed that cladodes produce these pigments only in the winter season. In all the species, the higher content of betacyanins was reached in the fruits from the second bloom, with O. stricta being the most rich. The amount of betacyanins is comparable to some commercial red beets used as a common source of betacyanins as natural food color.

Ultrastructural and cytochemical study of Plocamium cartilagineum (Plocamiales, Rhodophyta) from Ross Sea (Antarctica)

Abstract Morphological, ultrastructural, and cytochemical characteristics of the red alga Plocamium cartilagineum from Antarctica have been studied and compared with those of the same species from the Mediterranean Sea. Distinct regions with possibly different functions were recognisable in the bushy thallus of Plocamium cartilagineum. Chloroplasts were concentrated in the outermost cell layer, while in the other cortex cells abundant floridean starch accumulated. No starch was found in the large medullary cells, characterised by the insertion in their walls of several large and lenticular pit connections devoid of plug caps and proteic in nature. Sulphated polysaccharides were distributed in the extracellular compartments of all the regions of the thallus, except in the surface layer. These acidic phycocolloids were particularly concentrated in the cell wall proper, which also exhibited a well organised fibrillar component probably consisting of cellulose. The distinctive feature of the Antarctic thalli, compared with the Mediterranean ones, was the lack, in the former, of recognisable phycobilisomes on the thylakoid surfaces. This peculiarity had already been noticed in the other Antarctic red alga Iridaea cordata, collected, like Plocamium cartilagineum, in summer and from ice‐free waters. The loss of phycobilisomes may be a defence mechanism activated by benthic shade‐adapted red algae from Antarctica to protect the photosynthetic apparatus against damage from high light intensities.

Morphological, Ultrastructural and photosynthetic features of two freshwater angiosperms.

Colonization of the aquatic environment by flowering plants has required the evolution of morphological and physiological adaptative mechanisms useful to face the numerous limiting factors which can make it difficult for a macrophyte to live in water.