Belén Márquez-García

Glutathione in plants: an integrated overview.

Plants cannot survive without glutathione (γ-glutamylcysteinylglycine) or γ-glutamylcysteine-containing homologues. The reasons why this small molecule is indispensable are not fully understood, but it can be inferred that glutathione has functions in plant development that cannot be performed by other thiols or antioxidants. The known functions of glutathione include roles in biosynthetic pathways, detoxification, antioxidant biochemistry and redox homeostasis. Glutathione can interact in multiple ways with proteins through thiol-disulphide exchange and related processes. Its strategic position between oxidants such as reactive oxygen species and cellular reductants makes the glutathione system perfectly configured for signalling functions. Recent years have witnessed considerable progress in understanding glutathione synthesis, degradation and transport, particularly in relation to cellular redox homeostasis and related signalling under optimal and stress conditions. Here we outline the key recent advances and discuss how alterations in glutathione status, such as those observed during stress, may participate in signal transduction cascades. The discussion highlights some of the issues surrounding the regulation of glutathione contents, the control of glutathione redox potential, and how the functions of glutathione and other thiols are integrated to fine-tune photorespiratory and respiratory metabolism and to modulate phytohormone signalling pathways through appropriate modification of sensitive protein cysteine residues.

Phenolics composition in Erica sp. differentially exposed to metal pollution in the Iberian Southwestern Pyritic Belt

The phenolic composition of different populations of Erica andevalensis,E. australis and E. arborea was analyzed according to the different degree of exposition to metals in soils. E. andevalensis populations, highly exposed to metal pollution, had the lowest total phenol content and the lowest antioxidant activity measured as trolox equivalents. The HPLC analysis of leaf extracts revealed that phenolic composition in all analyzed populations of E. australis and E. arborea was very similar, although wild populations were differentially exposed to metal pollutions. However, E. andevalensis showed a phenolic profile characterized by the absence of many phenolic compounds quantified in the other species, although two compounds derived from cinnamic and coumaric acids were exclusively observed in this species.

Effects of Cadmium on Phenolic Composition and Antioxidant Activities of Erica andevalensis

We evaluated the effects of cadmium on phenolic composition of Erica andevalensis, an endemic protected heather that grows in mine affected soils. Plants cultivated under laboratory-controlled conditions were exposed to acute doses of cadmium to investigate the mechanisms this species possesses to survive in the presence of toxic metals in its natural habitat. Cadmium increased the total levels of phenolics and flavonoids compounds, and the total antioxidant capacity. Cinnamic acid derivatives, epicatechin, and rutin were increased in the presence of cadmium when applied in levels that did not alter the ratio of chlorophylls. Phenolic compounds play an important role in the metabolism of E. andevalensis to survive in heavy metal polluted soils.

A new role for glutathione in the regulation of root architecture linked to strigolactones.

Reduced glutathione (GSH) is required for root development, but its functions are not characterized. The effects of GSH depletion on root development were therefore studied in relation to auxin and strigolactone (SL) signalling using a combination of molecular genetic approaches and pharmacological techniques. Lateral root (LR) density was significantly decreased in GSH synthesis mutants (cad2-1, pad2-, rax1-), but not by the GSH synthesis inhibitor, buthionine sulfoximine (BSO). BSO-induced GSH depletion therefore did not influence root architecture in the same way as genetic impairment. Root glutathione contents were similar in the wild-type seedlings and max3-9 and max4-1 mutants that are deficient in SL synthesis and in the SL-signalling mutant, max2-1. BSO-dependent inhibition of GSH synthesis depleted the tissue GSH pool to a similar extent in the wild-type and SL synthesis mutants, with no effect on LR density. The application of the SL analogue GR24 increased root glutathione in the wild-type, max3-9 and max4-1 seedlings, but this increase was absent from max2-1. Taken together, these data establish a link between SLs and the GSH pool that occurs in a MAX2-dependent manner.

Antioxidants in Erica andevalensis: A comparative study between wild plants and cadmium-exposed plants under controlled conditions

Erica andevalensis is an endemic species from SW Iberian Peninsula, always growing in metal-enriched and acid soils. In the present study, a comparison was made between wild E. andevalensis plants collected from the field and cultivated ones exposed to different cadmium levels (0, 0.5, 5 and 50 μM). Wild plants contain higher levels of ascorbic acid (around 8000 nmol g(-1) FW) than lab-cultivated control plants (around 3000 nmol g(-1) FW). Glutathione levels follow an opposite trend being smaller in wild plants than lab-cultivated ones. Moreover, the total antioxidant capacity of wild plants is 90 times higher than in cultivated plants non-exposed to cadmium. Cadmium treatment of lab-cultivated plants did not affect the growth of E. andevalensis or the glutathione levels. However, the total antioxidative capacity increased in plants exposed to 50 μM of cadmium. Cadmium was added to the soil and it was transported into leaves reaching levels of 3.299 ± 0.781 μg Cd/g DW in plants exposed to 50 μM. These results underline a possible importance of antioxidants in the metal tolerance show by the high antioxidant capacity detected in both wild and lab-cultivated plants exposed to high cadmium levels.

Strigolactones spatially influence lateral root development through the cytokinin signaling network

Highlight Strigolactones monitor lateral root development in a spatiotemporal manner by an interplay with cytokinin.

Antioxidative system and oxidative stress markers in wild populations of Erica australis L. differentially exposed to pyrite mining activities.

Erica australis L. is a widely distributed shrub able to grow in a variety of environments. In the Iberian Pyritic Belt (SW Spain and Portugal), E. australis can be observed growing successfully in very acidic and highly metal-enriched soils. However, no data about the metal tolerance of this plant in wild populations have been reported so far. In this study, we have analysed metal contents in the leaves of E. australis from three wild populations growing in soils affected by metals in different ways (mine wastes, the terrace of a river affected by acid mine drainage and soils not affected by mining activities but enriched in metals due the geology of the area) and, taking into account that metals may generate reactive oxygen species, we also assayed the oxidative damages and the antioxidative defences. All plants contained high levels of Fe and Mn in the leaves, but plants exposed to mining activities also accumulate different levels of As, Ni, Mo, Pb, and Zn depending on the population considered. Our data show that E. australis responds to metal-catalysed production of reactive radicals by oxidising ascorbic acid, which is present at concentrations much higher than described in other plant species, but it is highly oxidised, close to 40%. Ascorbic acid may counteract reactive oxygen species, and no cell damage was produced, as shown by the low levels of H(2)O(2) and lipid peroxidation found compared with other plant species and no damage reflected in pigment levels.

The effects of heavy metals on germination and seedling characteristics in two halophyte species in Mediterranean marshes

The influence of different concentrations (10-2000 μM) of heavy metals (Cu, Mn, Ni, Zn) was analysed in Atriplex halimus and Salicornia ramosissima germination pattern and seedling size. They are two halophyte species that grow in the Estuary of Huelva (Southwest Iberian Peninsula, Spain), one of the most heavy metal-polluted environments in the world. All of the metals tested affected the final germination percentage in A. halimus and only Ni reduced germination in S. ramosissima. The germination rate was unaffected in both species. The study of seedling development shows that S. ramosissima, an intertidal annual species, has a higher tolerance of metals than A. halimus, a bush that inhabits the upper part of the marshes. Taking into account the metal concentrations in the estuary and the effects of these on the seedling development of the species analysed, we conclude that metals might limit plant colonisation in some parts of the marshes.

Pollen production in halophytic species of the Chenopodiaceae in a Mediterranean marsh

Abstract The pollen production per anther has been analysed in ten species of Chenopodiaceae that grow in the salt marshes of the Marismas del Odiel Natural Park (Huelva, south-west Spain). The mean pollen production per anther is 5819, ranged from 580 in Salicornia ramosissima to 12 467 in Salsola vermiculata, and is related to the size of the anthers. In six of the species, pollen production per anther has been studied in two populations and a strong interaction between species and populations was found. Pollen production of central and lateral flowers has been compared in four species, showing that central flowers produce significantly more pollen than lateral ones. In Arthrocnemum macrostachyum, a comparison between the pollen production of upper and lower stamens was performed and no significant differences were found. The pollen/ovule (P/O) ratio has been estimated for each of the species studied for the monoecious species, using the previously calculated male flower/female flower ratio. The monoecious species have the highest P/O ratios, followed by those with hermaphrodite flowers and allogamous reproduction. The lowest P/O ratios were found in Salicornia ramosissima (681) and Suaeda albescens (6025), possibly due to them being autogamous, which is consistent with the annual cycle and ecology of the species. The biggest value was found in the monoecious species Halimione portulacoides (88 405). In the remainder of the species, the P/O ratio depends on the density of individuals of each species in the communities.