Unveiling Fatty Acid Profiles of the Parasitic Plants Orobanche foetida Poiret. and Orobanche crenata Forsk. and Modulation of Faba Bean (Vicia faba L.) Fatty Acid Composition in Response to Orobanche Infestation.

Broomrapes (Orobanche spp.) are root parasitic plants that threaten agricultural production in many parts of the world. In this study, the effect of two orobanche species, Orobanche crenata and O. foetida, on faba bean plants was studied in Tunisia. The two orobanche species inhibited both biomass production and pod formation, decreased the chlorophyll (Chl) content and total lipid (TL), and enhanced electrolyte leakage (EL) and lipid peroxidation. Concomitantly, orobanche parasitism induced a lower degree of fatty acid (FA) unsaturation due to a shift in the FA composition. On the other hand, with regard to orobanche seeds, oleic and linoleic acids were the predominant FA in the two orobanche species. After orobanche seed germination and penetration of host tissues, all the orobanche development stages showed a decrease in the TL content and changes in the FA composition in comparison to orobanche seeds. The level of TL was equal to or lower in all parasite development stages (except for S4) than that in the roots and leaves of healthy faba bean plants. These results suggest that the negative effect of orobanche infestation on faba bean development can be attributed to the reduced chlorophyll content and alteration in membrane stability attested by the reduced TL level and FA unsaturation.

Exogenous nitric oxide alleviates manganese toxicity in bean plants by modulating photosynthesis in relation to leaf lipid composition.

Nitric oxide (NO) is a signaling molecule controlling several steps of plant development and defense process under stress conditions. NO-induced alleviation of manganese (Mn) toxicity was investigated on bean plants submitted for 28 days to 500 µM MnCl2. Manganese excess decreased plant dry weight and elongation and increased levels of reactive oxygen species and lipid peroxidation leading to up-regulation of superoxide dismutase, catalase, and ascorbate peroxidase activities. The inhibitory effects of Mn on plant growth were associated to reduction of light-saturated carbon assimilation (Amax), stomatal conductance (gs), and transpiration (E). By contrast, Mn induced significant increase in the apparent quantum yield (ɸ) and light compensation point (LCP). Interestingly, intracellular CO2 (Ci) remains stable under Mn stress. Concomitantly, leaf membrane lipids have drastically reduced under high Mn concentration. After Mn exposition, leaf fatty acids exhibited a significant loss of linolenic acid, accompanied by an accumulation of palmitoleic, stearic, and linoleic acids leading to alteration of lipid desaturation. NO supply reversed Mn toxicity as evidenced by enhancement of growth biomass and recovery of Amax, E, ɸ, and LCP. Similarly, NO addition has positive effects on leaf lipid content and composition leading to restoration of lipid unsaturation. The modulation of fatty acid composition can be a way to reduce leaf membrane damages and maintain optimal photosynthesis and plant growth. Despite the absence of enough evidences in how NO is involved in lipid and photosynthesis recovery under Mn stress conditions, it is assumed that NO beneficial effects are attributable to NO/Mn cross-talk.

Alleviation of cadmium-induced genotoxicity and cytotoxicity by calcium chloride in faba bean (Vicia faba L. var. minor) roots.

Alleviation of cadmium-induced root genotoxicity and cytotoxicity by calcium chloride (CaCl2) in faba bean (Vicia faba L. var. minor) seedlings were studied. Faba bean seeds were treated with H2O or 2% CaCl2 for 6 h before germination. Seeds were then exposed to 0 and 50 µM CdCl2 concentrations for 7 days. Genotoxic damaging effects of Cd was examined through the determination of the mitotic index (MI), chromosomal aberrations (CA) and micronucleus (MN) in the meristem cells of faba bean roots. Similarly, effects of Cd stress on metal accumulation, total membrane lipid contents, total fatty acid composition (TFA), lipid peroxidation as indicated by malondialdehyde production, soluble protein and non-protein thiols (NP-SH) contents, hydrogen peroxide production and the activities of superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPX) were evaluated after 7 days of Cd stress in the seedling roots. Cd stress resulted in the reduction of MI, in addition to MN formation and CA induction in the roots of non-primed seeds (treated with H2O). Moreover, Cd induced lipid peroxidation, H2O2 overproduction and loss of membrane lipid amount and soluble protein content, and changes in the TFA composition in roots of faba bean seedlings. SOD activity declined, but CAT and GPX activities increased. However, seed pre-treatment with CaCl2 attenuated the genotoxic and cytotoxic effects of Cd on Vicia faba roots. The results showed that CaCl2 induced reduction of Cd accumulation, improved cell membrane stability and increased the antioxidant defence systems, thus reducing and alleviating Cd genotoxicity and oxidative damage.

Drought priming improves subsequent more severe drought in a drought-sensitive cultivar of olive cv. Chétoui.

Drought is a major factor limiting crop production worldwide. The objective of this study was to test whether pre-exposure to drought can enhance the subsequent drought response of a drought-sensitive variety of olive cv. Chétoui. Seven-months old olive plants were grown in a controlled conditions and divided into control plants (irrigated daily), primed plants (PP, primed by exposure to drought for 21 days, re-watered for 60 days and then exposed to water depletion for 30 days) and non-primed plants (NPP, well watered for 81 days and immediately followed by intermediate drought as PP). Compared to the non-primed plants, primed plants showed an improvement in biomass production and healthy values of photosynthesis parameters with a higher accumulation of photosynthetic pigments. Additionally, the data of chlorophyll fluorescence were significantly similar to those of control, implying that no photodamage was occurred. Moreover, primed plants exhibited high accumulation of total sugar and proline which lead to the better water status maintenance. The lower level of oxidative status measured in term of hydrogen peroxide (H2O2), malondiadehyde (MDA) and electrolyte leakage (EC) in primed plants confirmed the alleviation of oxidative stress. Furthermore, the primed plants possessed more effective oxygen scavenging systems as exemplified by the increased activities of CAT, SOD, GP and high accumulation of polyphenols, resulting in a better maintenance in homeostasis of ROS production. Our investigation is indicative of the result of the benefit memory effects caused by stress pre-exposure in young olive plants cv.'Chétoui' to overcome subsequent stress.

Changes in chloroplast lipid contents and chloroplast ultrastructure in Sulla carnosa and Sulla coronaria leaves under salt stress.

The possible involvement of chloroplast lipids in the mechanisms of NaCl tolerance was studied in leaves of two varieties of Fabaceae: Sulla carnosa and Sulla coronaria, which were subjected to 200mM NaCl over 20days. Changes in membrane lipid peroxidation, chloroplast lipids content, fatty acids (FA) composition and the ultrastructure of chloroplasts under salt stress were investigated. Chloroplast lipids were separated and quantified by high performance liquid chromatography coupled to evaporative light scattering detection (HPLC/ELSD). The results showed that salinity induced a significant decrease in digalactosyldiacylglycerol (DGDG), phosphatidylglycerol (PG) and sulfoquinovosylglycerol (SQDG) content in both S. carnosa and S. coronaria leaves, whereas monogalactosyldiacylglycerol (MGDG) content did not change significantly in S. carnosa leaves. The MGDG/DGDG ratio remained stable in S. coronaria leaves but increased in those of S. carnosa. In addition, the unsaturated-to-saturated fatty acids ratio (UFAs:SFAs) did not change under salt stress in S. coronaria leaves, while it decreased significantly in S. carnosa leaves. Moreover, salinity did not induce significant changes in MGDG and DGDG unsaturation level in S. carnosa leaves, in contrast to S. coronaria, in which salinity seems to enhance the unsaturation level in MGDG, DGDG and PG. Furthermore, the level of membrane lipid peroxidation, as expressed by malondialdehyde (MDA) levels, increased at 200mM in S. carnosa leaves, while it did not change significantly in those of S. coronaria. With respect to the ultrastructure of chloroplasts at 200mM NaCl, investigated by transmission electron microscopy (TEM), salt-stress caused the swelling of thylakoids in S. carnosa mesophyll. These ultrastructural changes were observed especially in the spongy tissue in S. coronaria. Taken together, these findings suggest that the stability of MGDG/DGDG ratio, the unchanged unsaturation level, and increasing unsaturation level in MGDG, DGDG and PG may be effective to some degree in suppressing the ultrastructural damage caused by salinity effects and may contribute to protect the chloroplast membrane integrity against salt stress.

Growth capacity and biochemical mechanisms involved in rhizobia tolerance to salinity and water deficit.

The aim of the present study was to evaluate abiotic stress tolerance of rhizobial strains belonging to Mesorhizobium, Sinorhizobium, and Rhizobium genera, as well as to investigate specie specific stress response mechanisms. Effect of NaCl and PEG on growth capacity, protein, lipid peroxydation (MDA), membrane fatty acid composition and antioxidant enzymes were investigated. Growth capacity and viability of overall rhizobia strains decreased proportionally to the increase of NaCl and PEG levels in the medium. Sinorhizobium strains appeared the most tolerant, where 4H41strain was able to grow at 800 mM NaCl and 40% PEG. On the other hand, growth of R. gallicum and M. mediterraneum was inhibited by 200 mM NaCl. The content of MDA was unchanged in Sinorhizobium strains under both stresses. For Mesorhizobium, only PEG treatment increased the content of MDA. Amount of the C19:0 cyclo fatty-acid was increased in both Sinorhizobium and Mesorhizobium tolerant strains. NaCl stress increased Superoxide dismutase (SOD) activity of overall species; especially the most tolerant strain 4H41. Both treatments increased catalase (CAT) activity in 4H41, TII7, and 835 strains. Obtained results suggest that major response of tolerant Sinorhizobium and Mesorhizobium strains to NaCl and PEG stresses is a preferential accumulation of the C19:0 cyclo fatty acid within bacterial membrane as mechanism to reduce fluidity and maintain integrity. Cell integrity and functioning is also assured by maintaining and/or increasing activity of SOD and CAT antioxidant enzymes for tolerant strains to omit structural and functional damages related to reactive oxygen species overproduced under stressful conditions.

Medicago sativa--Sinorhizobium meliloti Symbiosis Promotes the Bioaccumulation of Zinc in Nodulated Roots.

In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn, Ca, Fe, and Mg) partitioning and nodulation of Medicago sativa This plant was cultivated with and without Zn (2 mM). Treatments were plants without (control) and with Zn tolerant strain (S532), Zn intolerant strain (S112) and 2 mM urea nitrogen fertilisation. Results showed that M. sativa germinates at rates of 50% at 2 mM Zn. For plants given nitrogen fertilisation, Zn increased plant biomass production. When grown with symbionts, Zn supply had no effect on nodulation. Moreover, plants with S112 showed a decrease of shoot and roots biomasses. However, in symbiosis with S532, an increase of roots biomass was observed. Plants in symbiosis with S. meliloti accumulated more Zn in their roots than nitrogen fertilised plants. Zn supply results in an increase of Ca concentration in roots of fertilised nitrogen plants. However, under Zn supply, Fe concentration decreased in roots and increased in nodules of plants with S112. Zn supply showed contrasting effects on Mg concentrations for plants with nitrogen fertilisation (increase) and plants with S112 (decrease). The capacity of M. sativa to accumulate Zn in their nodulated roots encouraged its use in phytostabilisation processes.

Changes in content and fatty acid profiles of total lipids of two halophytes: Sesuvium portulacastrum and Mesembryanthemum crystallinum under cadmium stress.

Changes in lipid content and fatty acid composition were determined in leaves of two halophytes: Sesuvium portulacastrum and Mesembryanthemum crystallinum exposed to cadmium (Cd). Experiments were carried out using young small-sized plants grown hydroponically (S. portulacastrum) or aseptically germinated seeds (M. crystallinum). Cd treatment was applied at different concentrations (0, 50, 100 and 200microM) for 30 days. At high cadmium doses (200microM), contents of total lipids (TL) and lipid fractions including galactolipids (GL), phospholipids (PL) and neutral lipids (NL) decreased more in M. crystallinum leaves than in S. portulacastrum leaves. Moreover, there were no significant changes in the total fatty acid composition of S. portulacastrum leaves during metal treatment. In contrast, M. crystallinum leaves showed a decrease in the percentage of the tri-unsaturated fatty acid (C18:3), and a corresponding increase in the percentage of di-unsaturated fatty acid (C18:2). These different responses suggested that S. portulacastrum seems to be more feasible for phytoremediation.

Cadmium effects on growth and mineral nutrition of two halophytes: Sesuvium portulacastrum and Mesembryanthemum crystallinum.

Growth, cadmium accumulation and potassium and calcium status were studied in two halophytes from Aizoaceae family: Sesuvium portulacastrum and Mesembryanthemum crystallinum. After multiplication, the seedlings were cultivated on nutrient solution supplemented with NaCl (100mM) and CdCl2 (0, 50, 100, 200 and 300 microM). After 1 month of treatment, plants were harvested and the dry weight, as well as the Cd, K and Ca concentrations in tissues were determined. Results showed that S. portulacastrum, a perennial halophyte with slow growth, is significantly more tolerant to Cd than M. crystallinum, an annual plant. Cd severely inhibited Mesembryanthemum growth even at the lowest Cd concentration in culture medium (50 microM), and did not modify significantly that of Sesuvium. For both halophytes, Cd accumulation was significantly higher in the roots than in the shoots. However, Cd concentration reached 350-700 microg g(-1) DM in the shoots, values characteristic of Cd hyperaccumulator plants. The addition of Cd in the culture medium led to a disturbance of Ca and especially K nutrition, suggesting the possibility to improve plant growth and Cd phytoextraction of both halophytes by increasing nutrient availability in the culture medium.

[Cadmium effects on lipid metabolism of rape (Brassica napus L.)]. / Effets du cadmium sur le métabolisme des lipides de plantules de colza (Brassica napus L.).

Treatment of rape seedlings with increasing CdCl2 concentrations in the culture medium resulted in a cadmium accumulation within plant tissues, which increased with external metal dose; such accumulation was more important in roots than in leaves. Biomass production was severely inhibited, even at low cadmium concentration. In leaves, quantities of chloroplastic lipids, monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfolipids (SL) and phosphatidylglycerol (PG) decreased sharply under metallic treatment. However, contents of extrachloroplastic lipids, mainly phosphatidylcholine (PC) and phosphatidylethanolamine (PE) increased significantly. In contrast to leaves, contents of root phospholipids decreased. Likewise, levels of tri-unsaturated fatty acids: linolenic (C18:3) and hexadecatrienoïc (C16:3) dropped in leaves of treated seedlings as compared to those of controls, suggesting that heavy metals induced an alteration in the fatty acid desaturation process or a stimulation of their peroxidation. Also, trans palmitoleic acid (C16:1-trans) level in PG decreased considerably. In roots, there was a slight decrease in C18:3 level, with a concomitant increase in the C18:2 percentage. Radioactive labelling of leaf lipids with (1-14C) acetate allowed to show that fatty acid biosynthesis was noticeably altered at the highest cadmium dose used (50 microM). Biosynthesis of tri-unsaturated fatty acids was also inhibited which may explain the decline in non-labelled lipid contents. Results showed that metallic ion seems to affect selectively chloroplastic membranes due to an inhibition of polyunsaturated fatty acid biosynthesis. Moreover, a lipid peroxidation occurred in our case because of the spectacular increase of malondialdehyde (MDA) content observed in cadmium treated leaves.