Comparative effects of arsenite (As(III)) and arsenate (As(V)) on whole plants and cell lines of the arsenic-resistant halophyte plant species Atriplex atacamensis.

Whole plants and hypocotyl-derived calli of the halophyte plant species Atriplex atacamensis were exposed to 50 µM arsenate (As(V)) or 50 µM arsenite (As(III)). At the whole plant level, As(III) was more toxic than As(V): it reduced plant growth, stomatal conductance, photosystem II efficiency while As(V) did not. In roots, As accumulated to higher level in response to As(III) than in response to As(V). Within root tissues, both arsenate and arsenite were identified in response to each treatment suggesting that oxidation of As(III) may occur. More than 40% of As was bound to the cell wall in the roots of As(V)-treated plants while this proportion strongly decreased in As(III)-treated ones. In leaves, total As and the proportion of As bound to the cell wall were similar in response to As(V) and As(III). Non-protein thiol increased to higher extent in response to As(V) than in response to As(III) while ethylene synthesis was increased in As(III)-treated plants only. Polyamine profile was modified in a contrasting way in response to As(V) and As(III). At the callus level, As(V) and As(III) 50 µM did not reduce growth despite an important As accumulation within tissues. Calli exposed to 50 µM As did not increase the endogenous non-protein thiol. In contrast to the whole plants, arsenite was not more toxic than arsenate at the cell line level and As(V)-treated calli produced higher amounts of ethylene and malondialdehyde. A very high dose of As(V) (1000 µM) strongly reduced callus growth and lead to non-protein thiols accumulation. It is concluded that As(III) was more toxic than As(V) at the plant level but not at the cellular level and that differential toxicity was not fully explained by speciation of accumulated As. Arsenic resistance in A. atacamensis exhibited a cellular component which however did not reflect the behavior of whole plant when exposed to As(V) or As(III).

Polyamine and tyramine involvement in NaCl-induced improvement of Cd resistance in the halophyte Inula chrithmoides L.

The aim of the present work was to analyze the impact of salinity on the plant response to Cd toxicity in the Mediterranean halophyte species Inula crithmoides. For this purpose, cuttings were cultivated hydroponically during 21d in the presence of 0, 25 or 50µM CdCl2 combined or not with 0, 100, 200 and 400mM NaCl. The obtained data demonstrated that, in the absence of Cd, NaCl strongly increased plant growth (the maximal dry weight being observed at 100mM) and enhanced the Na+/K+ ratio in the shoot. Cd alone strongly affected plant growth in this halophyte. However, in Cd-treated plants, NaCl protected Inula crithmoides from Cd toxicity and contributed to reduce Cd absorption and translocation. Small aliphatic polyamine (putrescine, spermidine, spermine) increased in response to both NaCl and CdCl2, the highest concentration in plants being observed when both agents are present in the medium. The recorded increase preferentially concerned the polyamine bound fraction, which might be related to their involvement in the protection of endogenous cellular structures. The aromatic monoamine tyramine also strongly increased in response to Cd toxicity and its putative role is discussed in relation to conjugation processes. Salinity and Cd increased ammonium/nitrate ratio in leaves and roots and the involvement of stress-induced modification of N nutrition on polyamine oversynthesis is also discussed.

Phosphorus deficiency modifies As translocation in the halophyte plant species Atriplex atacamensis.

Most arsenic in surface soil and water exists primarily in its oxidized form, as arsenate (As(V); AsO43-), which is an analog of phosphate (PO43-). Arsenate can be taken up by phosphate transporters. Atriplex atacamensis Phil. is native to northern Chile (Atacama Desert), and this species can cope with high As concentrations and low P availability in its natural environment. To determine the impact of P on As accumulation and tolerance in A. atacamensis, the plants were cultivated in a hydroponic system under four treatments: no As(V) addition with 323µM phosphate (control); 1000µM As(V) addition with 323µM phosphate; no As(V) and no phosphate; 1000µM As(V) addition and no phosphate. Phosphate starvation decreased shoot fresh weight, while As(V) addition reduced stem and root fresh weights. Arsenate addition decreased the P concentrations in both roots and leaves, but to a lesser extent than for P starvation. Phosphorus starvation increased the As concentrations in roots, but decreased it in shoots, which suggests that P deficiency reduced As translocation from roots to shoots. Arsenate addition increased total glutathione, but P deficiency decreased oxidized and reduced glutathione in As(V)-treated plants. Arsenate also induced an increase in S accumulation and nonprotein thiol and ethylene synthesis, and a decrease in K concentrations, effects that were similar for the P-supplied and P-starved plants. In contrast, in As(V)-treated plants, P starvation dramatically decreased total soluble protein content and increased lipid peroxidation, compared to plants supplied with P. Phosphorus nutrition thus appears to be an important component of A. atacamensis response to As toxicity.

Combined transcriptomic and physiological approaches reveal strong differences between short- and long-term response of rice (Oryza sativa) to iron toxicity.

Ferrous iron toxicity is a mineral disorder frequently occurring under waterlogged soils where rice is cultivated. To decipher the main metabolic pathways involved in rice response to iron excess, seedlings have been exposed to 125 mg L(-1) FeSO(4) for 3 weeks. A combined transcriptomic, biochemical and physiological study has been performed after short-term (3 d) or long-term (3 weeks) exposure to iron in order to elucidate the strategy of stress adaptation with time. Our results showed that short- and long-term exposure involved a very different response in gene expression regarding both the number and function. A larger number of genes were up- or down-regulated after 3 d than after 3 weeks of iron treatment; these changes also occurred in shoot even though no significant difference in iron concentration was recorded. Those modifications in gene expression after 3 d affected not only genes involved in hormonal signalling but also genes involved in C-compound and carbohydrate metabolism, oxygen and electron transfer, oxidative stress, and iron homeostasis and transport. Modification in some gene expression can be followed by modification in corresponding metabolic products and physiological properties, or differed in time for some others, underlying the importance of an integrated study.

Arsenic accumulation and distribution in relation to young seedling growth in Atriplex atacamensis Phil.

Even at trace levels, arsenic is of environmental and health concern due to its high toxicity. The xerohalophyte plant species Atriplex atacamensis grows on an arsenic-contaminated mining area in North Chile. Young seedlings that were grown from seeds collected from these plants were grown in a nutrient solution under controlled environmental conditions and were exposed for 14 and 28 days to 0, 100 or 1000 µM arsenate. More than 75% of the plants that were exposed to the highest As dose survived until the end of the treatment. The seedling growth was reduced (100 µM As) or inhibited (1000 µM As) in the stress conditions, but the plants were able to efficiently close their stomata and perform osmotic adjustments to avoid secondary water stress. Arsenic accumulated up to 400 µg g(-1) DW in the shoots and 3500 µg g(-1) DW in the roots. Arsenate drastically impaired the P content and increased glycinebetaine content, although no arsenobetaine was found in the tissues. With the exception of arsenite and arsenate, no As-containing organic compound was detected. Arsenic was not excreted by the trichomes that were present at the leaf surface. Although an increase in the total level of non-protein thiols suggested that arsenite fixation on the sulfhydryl groups could occur in the stressed tissues, the majority of the soluble arsenic remained in its oxidized state As(V). Arsenate induced an increase in the free soluble polyamine concentrations in all of the organs, and it increased the proportion of spermidine and spermine and decreased the proportion of putrescine in the polyamine pool. Therefore, it is likely that these polycationic molecules may assist in arsenate sequestration in the stressed tissues, and A. atacamensis may represent a promising plant species that can be tested in field trials for its phytomanagement of As-contaminated sites in desert areas.