NaCl alleviates polyethylene glycol-induced water stress in the halophyte species Atriplex halimus L.

Abstract

Atriplex halimus L. is a C4 xero-halophyte species well adapted to salt and drought conditions. To collect information on the physiological impact of low salt levels on their water-stress resistance, seedlings were exposed for 6 d to nutrient solution containing either 0% or 15% polyethylene glycol 10,000 (PEG), in the presence or in the absence of 50 mM NaCl. Similar experiments were performed with one PEG-resistant and one PEG-sensitive selected cell line exposed for 50 d to 0% or 15% PEG on standard Linsmaier and Skoog (LS) medium, on LS medium supplemented with 50 mM NaCl, or on Na+-free medium. NaCl mitigated the deleterious impact of PEG on growth of both whole plants and PEG-sensitive cell lines and improved the ability of stressed tissues to perform osmotic adjustment (OA). Water stress reduced CO2 net assimilation rates quantified in the presence of high CO2 and low O2 levels (A), stomatal conductance and transpiration, but NaCl improved water use efficiency of PEG-treated plants through its positive effect on A values, especially in young leaves. PEG increased the internal Na+ concentration. The resistant cell line accumulated higher concentration of Na+ than the PEG-sensitive one. The complete absence of Na+ in the medium endangered the survival of both cell lines exposed to PEG. Although Na+ by itself contributed only for a small part to OA, NaCl induced an increase in proline concentration and stimulated the synthesis of glycinebetaine in response to PEG in photosynthetic tissues. Soluble sugars were the main contributors to OA and increased when tissues were simultaneously exposed to PEG and NaCl compared with PEG alone, suggesting that Na+ may influence sugar synthesis and/or translocation.

The tolerance of Atriplex halimus L. to environmental stresses

“…Martí nez et al (2005) ascribed improved growth at 50 mM NaCl to possible Na + enhancement of photosynthesis and sugar synthesis and/or transport. Boughalleb et al (2009) related enhanced growth to improvements in stomatal conductance, transpiration and CO 2 assimilation at moderate external NaCl levels (< 300 mM); Khedr et al (2011) suggested that vacuolar Na + accumulation increases cell volume and the photoassimilatory surface area of the leaves, stimulating growth.…”

“…Like other halophytes, A. halimus accumulates the ions responsible for salinity -Na + (Martí nez et al, 2005;Nemat Alla et al, 2012) and Cl -and other anions (Ben Ahmed et al, 1996;Ben Hassine et al, 2009) -in its tissues and is able to compartmentalise them in the vacuole due to efficient intracellular transport (Khedr et al, 2011). This osmotic adjustment (OA, the active intracellular accumulation of osmolytes) generates low values of tissue Ψ w ; even-lower coincident values of osmotic potential (Ψ s ) (e.g., -7.5 MPa; Bajji et al, 1998) maintain tissue turgor.…”

Alterações no perfil de frações nitrogenadas em calos de cana-de-açúcar induzidas por deficit hídrico

“…Essa observação indica que a resposta exibida por células isoladas ou por calos pode ser diferente daquela apresentada pela planta inteira. Alguns trabalhos têm demonstrado que uma resposta observada in vitro pode ter ou não relação com uma resposta da planta inteira (Bajji et al, 1998;Martinez et al, 2005). Essa diferença pode ser explicada pelo fato de a resistência ao estresse hídrico ser um caráter quantitativo, que envolve a expressão de diversos genes (Knight & Knight, 2001) e a ação de complexos mecanismos bioquímicos e fisiológicos, coordenados nos níveis de célula, tecido, órgão, planta inteira (Zhu, 2001 (2003), ao trabalhar com três cultivares de arroz, que diferem entre si quanto à resistência à seca e ao sal, observaram maior acúmulo de prolina nas radículas das cultivares tolerantes, expostas in vitro ao manitol e NaCl.…”

“…Tais proteínas podem ser sintetizadas "de novo" ou ter a expressão aumentada, em resposta ao estresse. Em cultura de tecidos, vários trabalhos têm sido realizados para esclarecer o papel de ambas as classes de solutos compatíveis (Bajji et al, 1998;Lutts et al, 2001;Martinez et al, 2005). Uma vez que muitos dos métodos empregados no melhoramento de espécies de propagação vegetativa utilizam a cultura de tecidos, a caracterização da resposta in vitro ao estresse hídrico é uma etapa indispensável em programas de melhoramento de plantas.…”

Cross Tolerance Mechanisms of Osmotic and Ionic Stress Adapted Cell Lines of Rice Towards Salinity

“…Martinez et al (2005) reported that in salt selected cell cultures of Brassica napus, B. juncea, Vigna radiata and Arabidopsis thaliana, tolerance to NaCl selected cell lines was considered as a general shift towards halophytic characteristics. On the other hand, restricted uptake of Na + and maintenance of K + level with enhanced growth under NaCl stress in LiCl adapted line could be the result of enhanced capacity of membranes for ionic discrimination like salt tolerance in glycophytes observed in NaCl tolerant cell lines of citrus, tobacco Medicago sativa, rice and M. sativa (Ben-Hayyim and Kochba, 1983;Shah et al, 1993), where the cells maintain a lower amount of Na + content under saline conditions.…”