TiO2 nanoparticles may alleviate cadmium toxicity in co-treatment experiments on the model hydrophyte Azolla filiculoides.

The hydrophyte Azolla filiculoides can be a useful model to assess if TiO2 NPs may in some way alleviate the Cd injuries and improve the ability of the plant to cope with this metal. With this mechanistic hypothesis, after a pre-treatment with TiO2 NPs, A. filiculoides plants were transferred to cadmium-contaminated water with or without TiO2 nanoparticles. After 5 days of treatment, cadmium uptake, morpho-anatomical, and physiological aspects were studied in plants. The continuous presence of TiO2 nanoparticles, though not increasing the uptake of cadmium in comparison with a priming treatment, induced a higher translocation of this heavy metal to the aerial portion. Despite the translocation factor was always well below 1, cadmium contents in the fronds, generally greater than 100 ppm, ranked A. filiculoides as a good cadmium accumulator. Higher cadmium contents in leaves did not induce damages to the photosynthetic machinery, probably thanks to a compartmentalization strategy aimed at confining most of this pollutant to less metabolically active peripheral cells. The permanence of NPs in growth medium ensured a better efficiency of the antioxidant apparatus (proline and glutathione peroxidase and catalase activities) and induced a decrease in H2O2 content, but did not suppress TBARS level.

Female gametophyte and embryo development in Helleborus bocconei Ten. (Ranunculaceae).

In this study, we investigated cytohistochemistry, cycle progression, and relative DNA content of the female gametophyte cells of Helleborus bocconei Ten. before and after fertilization process. The early stages of embryo development were also investigated. H. bocconei possesses a monosporic seven-celled/eight-nucleate Polygonum type female gametophyte, characterized by a morpho-functional polarity. The cells of the embryo sac showed abundant reserves of polysaccharides, strongly increasing in the egg cell just before fertilization. With different timing in DNA replication during cell cycle progression, synergids, egg cells, and polar nuclei showed a haploid DNA content at the end of their differentiation, while antipodes underwent three DNA endoreduplication cycles. Programmed cell death symptoms were detectable in synergid and antipodal cells. After double fertilization, the central cell quickly underwent many mitotic cycles forming the endosperm, which exhibited a progressive increase in protein bodies and starch grains. Close to the developing embryo, the endosperm differentiated a well-defined region rich in a fibrillar carbohydrate matrix. The zygote, that does not start immediately to divide after double fertilization, developed in to an embryo that reached the heart stage at fruit maturation time. A weakly differentiated embryo at this time indicates a morpho-physiological dormancy of seeds, as a survival strategy imposed by the life cycle of this plant with seed dispersal in spring and their germination in the following winter.

Plant adaptation to extreme environments: the example of Cistus salviifolius of an active geothermal alteration field.

Cistus salviifolius is able to colonise one of the most extreme active geothermal alteration fields in terms of both soil acidity and hot temperatures. The analyses of morpho-functional and physiological characters, investigated in leaves of plants growing around fumaroles (G leaves) and in leaves developed by the same plants after transfer into growth chamber under controlled conditions (C leaves) evidenced the main adaptive traits developed by this pioneer plant in a stressful environment. These traits involved leaf shape and thickness, mesophyll compactness, stomatal and trichome densities, chloroplast size. Changes of functional and physiological traits concerned dry matter content, peroxide and lipid peroxidation, leaf area, relative water and pigment contents. A higher reducing power and antioxidant enzymatic activity were typical of G leaves. Though the high levels of stress parameters, G leaves showed stress-induced specific morphogenic and physiological responses putatively involved in their surviving in active geothermal habitats.

Arsenic-induced morphogenic response in roots of arsenic hyperaccumulator fern Pteris vittata.

On the assumption that arsenic induces stress morphogenetic responses involved in As tolerance and hyperaccumulation in the Pteris vittata fern, we analyzed the root system of young sporophytes grown in 250, 334, and 500 µM As for five days and for 14 days. Anatomical and histological analyses were performed in plants grown for five days to evaluate the number, position, length and differentiation pattern of root hairs. AgNOR staining, employed to study nucleolus behavior in root apices, showed that arsenic influences nucleolar activity (evaluated by nucleolus size, number and absorbance) in the root meristem. In plants treated with 250 and 334 µM As an acropetal shift of root hair development and an increase in hair length and density were observed, linked to an ectopic pattern of differentiation. The opposite trend was recorded in plants treated with 500 µM As. It is worth noting the presence of living border-like cells, not yet observed in ferns, and their increase following As treatments. Analysis and vitality of border-like cells were surveyed after 14 days of treatments. In conclusion As treatments elicited a stress-induced morphogenic response which, by modifying the differentiation pattern, number and length of root hairs, modulating nucleolar activity and interacting with the rhizosphere by inducing border-like cell production, may adjust the rate of root uptake and its metabolic activity.