L. Sanità di Toppi

Response of barley plants to Fe deficiency and Cd contamination as affected by S starvation

Both Fe deficiency and Cd exposure induce rapid changes in the S nutritional requirement of plants. The aim of this work was to characterize the strategies adopted by plants to cope with both Fe deficiency (release of phytosiderophores) and Cd contamination [production of glutathione (GSH) and phytochelatins] when grown under conditions of limited S supply. Experiments were performed in hydroponics, using barley plants grown under S sufficiency (1.2 mM sulphate) and S deficiency (0 mM sulphate), with or without Fe(III)-EDTA at 0.08 mM for 11 d and subsequently exposed to 0.05 mM Cd for 24 h or 72 h. In S-sufficient plants, Fe deficiency enhanced both root and shoot Cd concentrations and increased GSH and phytochelatin levels. In S-deficient plants, Fe starvation caused a slight increase in Cd concentration, but this change was accompanied neither by an increase in GSH nor by an accumulation of phytochelatins. Release of phytosiderophores, only detectable in Fe-deficient plants, was strongly decreased by S deficiency and further reduced after Cd treatment. In roots Cd exposure increased the expression of the high affinity sulphate transporter gene (HvST1) regardless of the S supply, and the expression of the Fe deficiency-responsive genes, HvYS1 and HvIDS2, irrespective of Fe supply. In conclusion, adequate S availability is necessary to cope with Fe deficiency and Cd toxicity in barley plants. Moreover, it appears that in Fe-deficient plants grown in the presence of Cd with limited S supply, sulphur may be preferentially employed in the pathway for biosynthesis of phytosiderophores, rather than for phytochelatin production.

Response to Heavy Metals in Plants: A Molecular Approach

Heavy metal pollution causes a number of toxic symptoms both in higher plants and algae, e.g. growth retardation, inhibition of photosynthesis, induction and inhibition of enzymes, generation of oxidative stress. All plants cope with heavy metal stress by exploiting broad range of different response mechanisms acting in additive and/or synergistic way. Most common and important mechanisms comprise synthesis of metal-complexing peptides (glutathione, phytochelatins and related peptides), increased antioxidative enzymatic activity, synthesis of stress proteins (HSP), intracellular metal binding to nonprotein metal chelators like organic acids and phytate, release of extracellular, metal -binding exudates (composed of organic acids, amino acids, peptides, sugars and polysaccharides). Phytochelatins are regarded as potential biomarkers of heavy metal stress in plants.

Metal Chelating Peptides and Proteins in Plants

A group of metals having a density higher than 5 g cm−3 are generally termed as heavy metals (HM) and are toxic to plants when available in excess. However, a subset of them, at low concentrations, are essential micronutrients. Wild-type plants cope with HM stress (and homeostasis) by synthesizing a variety of chemically distinct metalchelating ligands (Figure 1), including organic acids, and by exploting a broad range of different response mechanisms, which may act in an additive and/or in a synergistic manner (Prasad, 2001). The main defence mechanisms involved in HM detoxification are revolved around the previously discussed “fan-shaped” model (Figure 2) (Sanita di Toppi and Gabbrielli, 1999), which is based on the “General Adaptation Syndrome” (GAS) hypothesis (Leshem and Kuiper, 1996; Selye, 1936). In this chapter, we focus on HM chelating peptides and proteins, with particular emphasis on phytochelatins. Updates on plant metallothioneins, ferritins and nicotianamine are given as well. Nonprotein metal chelators, in particular organic acids, single amino acids and phytin, not covered in this chapter, were recently reviewed by Rauser (1999).

Plant Response to Elevated Carbon Dioxide

In consequence of the current increase in atmospheric CO2 concentration, a large research effort has been devoted to clarifying the response of plants and ecosystems to this peculiar aspect of global change. The results have often been contradictory, also in consequence of the different experimental techniques. Through recent years, attention has moved from single physiological processes, often investigated in artificial environments with the risk of experimental artefacts, to the analysis of whole ecosystems, examined, as far as possible, in their natural conditions.The chapter reviews the technical development in fumigation facilities, and the main experimental results, focusing in particular on forests and grasslands, including lichens and mosses. The response of glasshouse grown horticultural plants is also outlined. Finally, attention is devoted to the effects of elevated CO2 on soil and hypogeous growth, mineral nutrition and soil microbial populations; on these topics, many questions are still open, and research appears to be promising.

Proteomic analysis in the lichen Physcia adscendens exposed to cadmium stress

This work was undertaken to explore the potential of proteomics to dissect parallel and consecutive events of cadmium stress response in the lichen Physcia adscendens (Fr.) H. Olivier. Thalli were exposed to 0 (control) and 36 microM Cd for 6, 18, 24 and 48 h. Two-dimensional electrophoresis and mass spectrometry analyses showed an 80-85% spot identity between 6 and 18 h vs. 24 and 48 h of Cd exposure. Putative heat-shock proteins and glutathione S-transferase generally increased their expression all over the Cd treatments. By contrast, ABC transporters were underexpressed after 6-18 h, but in some cases induced after 24-48 h of Cd exposure. The cytochrome P450 appeared to have a variable expression pattern over time. Overall these data suggest that a considerable importance in the response of P. adscendens thalli to Cd stress can be assumed by differential expression of various protein families.

Elevated CO2 reduces vessel diameter and lignin deposition in some legume plants grown in mini-FACE rings

Studies on stem (and leaf) structure and histology of a semi-natural grassland community, permanently growing in mini-FACE rings under elevated concentrations of atmospheric CO2 (560 μmol mol−1) are presented. Histochemical analysis of stem sections from legume plants grown under high CO2 concentration revealed both a reduction of lignin deposition in spring vascular bundles of Trifolium repens L., and a decrease in size of the xylem vessels in Vicia hybrida L. and Vicia sativa L. Thus, the effects of elevated CO2 on the stem histology of the species investigated are rather species-specific and/or organ-specific, and of major account especially in the early phases of vegetative growth, in particular as regards lignin deposition mechanisms. In leaves, neither differences as to lignification nor any other anatomical structure modification were found under CO2 enrichment.