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Hydroponic experiments were performed to investigate physiological mechanisms of selenium (Se) mitigation of As toxicity in sunflower. The exposure of plants to 10 μM arsenic (As) inhibited biomass production and intensively increased accumulation of As in both roots and leaves. As also enhanced hydrogen peroxides (H2O2) content and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. Presoaking seeds with Se (5, 10 and 20 μM) markedly alleviated the negative effect of As on plan growth and led to a decrease in oxidative damages as evidenced by the lowered H2O2 and MDA content. Se particularly enhanced the activities of catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX), but lowered that of superoxide dismutase (SOD). As important antioxidants, ascorbate (AsA) and glutathione (GSH) contents in sunflower leaves exposed to As were significantly decreased by Se treatment. These Original Research Article Issam et al.; JABB, 3(3): 101-109, 2015; Article no.JABB.2015.037 102 results reveal the potentiating effect of selenium in regulating Arsenic induced oxidative stress in sunflower seedling.

The effect of gibberellic acid on germination and seedling growth of lettuce variety, Vista, under salinity conditions was studied. A reduction in germination percentage, roots and shoots length and fresh weight were observed under salt stress. At the same time, acid phosphatase and phytase activities in roots were reduced by NaCl. The exogenous application of gibberellin increased germination percentage and improved length and fresh weight of roots and shoots under salt treatment. It also increased both acid phosphatase and phytase activities in roots under this constraint. The application of gibberellic acid compensated for the negative effect of salinity.Keywords: Acid phosphatase, germination, gibberellic acid, lettuce, phytase, salinity, seedling growth

Seeds of four lettuce (Lactuca sativa L.) genotypes viz., Great Lakes (GL), Paris Island cos, Kagraner Sommer (KS) and Isadora were assessed for their response to salt at the germination and seedling stages. The germination rate of the four varieties was comparatively studied under 0, 50, 100, 150 and 200 mM sodium chloride (NaCl) treatments. Differential response of genotypes to salt concentration was observed. Final germination percentage (FG%) decreased with increasing salinity in GL, Paris Island cos and Isadora varieties, and was annulated at the highest salt concentration in GL, the most sensitive variety. However, in the less sensitive, KS, FG% was decreased by 60% compared to the control at 200 mM. KS and GL varieties were selected as stress-tolerant and stress-sensitive varieties, respectively, and were used for further characterization. Dry weights (DWs) of radicles and hypocotyls were reduced by NaCl 100 and 150 mM in GL and only at 150 mM NaCl in KS. The activities of several antioxidant enzymes during germination were determined. Both varieties had the same malondialdehyde (MDA) content under 100 and 150 mM NaCl. The highest gaiacol peroxidise (GPX) activity was detected in GL seedlings at NaCl 50, 100 and 150 mM, respectively. Catalase (CAT) decreased at 50 and 100 mM NaCl, respecively. Total ascorbate (AsA + DHA) decreased in GL and increased significantly in KS. Our results suggest that tolerance of KS to salt may be due to a better protection mechanism against salinity induced oxidative damage relative to GL variety.Key words: Germination, lettuce, NaCl, growth, antioxidant activities, ascorbate.

Sulla constitutes an important genetic resource contributing to pastoral production, particularly in semi-arid regions. In Tunisia, seedlings of the southern species Sulla carnosa (Desf.) and the northern species Sulla coronaria (L.) were treated with NaCl (0, 100 and 200 mM) for 27 days. Salt treatments decreased leaf dry matter more in S. carnosa than in S. coronaria. S. coronaria accumulated less Na+ and greater amounts of K+ and showed greater K/Na selectivity, a trait which could be related to the maintenance of higher net K+ uptake and transport in the presence of NaCl. Pigments were severely affected by salt stress in leaves of S. carnosa when compared with leaves of S. coronaria. In addition to these physiological characterisations, genetic diversity was measured between the two accessions using inter simple sequence repeat (ISSR) markers. Three ISSR primers generated a total of 63 DNA amplicons for S. carnosa and 64 DNA amplicons for S. coronaria, all of which were polymorphic between the two accessions. Correlations between the molecular and physiological data revealed statistically significant correlations between the salt response of these two Sulla accessions and two molecular markers B340 and B860, in roots and shoots, respectively. S. coronaria showed greater salt tolerance on the basis of growth and K/Na selectivity, making it a good candidate for inclusion in a future breeding programme.Key words: Salt constraint, Sulla, growth, ISSR markers.

This experiment was conducted to evaluate the effects of osmopriming with KNO3 on germination traits, seedling growth and phosphatase activities of lettuce (Lactuca sativa L.) seeds under salinity condition. Lettuce seeds (Var. Vista) were primed with KNO3 (0.05%) for 2 h at 25°C in the dark. Primed and nonprimed seeds were germinated on distilled water containing 0 or 100 mM NaCl, for four days. Results show that germination percentage, root and shoot length and seedling fresh weight of primed seeds was higher than that of non-primed seeds in saline condition. Priming also increased acid phosphatase and phytase activities in the roots, shoots and cotyledons under salt stress. It seems that seed priming can be used for improving performance of lettuce seeds and seedlings grown under saline conditions.Key words: Osmopriming, lettuce, germination, salinity, acid phosphatase, phytase.

Hormonal priming is a pre-sowing treatment that improves seed germination performance and stress tolerance. To understand the physiology of hormonal priming and its association with post priming stress tolerance, we investigated the effect of hormonal priming with increasing gibberellic acid (GA 3 ) concentrations (0, 3, 4.5 and 6 mM) on seedling growth and antioxidant system in lettuce. Germination percentage was higher in lettuce seedlings derived from primed seeds. Radicle and hypocotyl length and dry weight were reduced by salt treatment to a greater extent in non-primed than in primed seeds. Hormonal priming with 4.5 mM GA 3 induced the most dramatic decreases in electrolyte leakage (EL) and malondialdehyde (MDA) levels. NaCl increased catalase (CAT) activity in primed and non-primed seeds. The total ascorbate level remained constant in both primed and non-primed seeds under NaCl constraint. These results suggest that hormonal priming might have increased the salt tolerance of lettuce seeds through enhancing the activities of antioxidant enzymes and reducing the membrane damage as estimated using EL and MDA biomarkers. Key words: Ascorbate, germination, hormonal priming, lettuce, salinity.

The inhibitory effect of salt stress on lettuce is one of the main reasons for the reduction of plant growth and crop productivity. In the present study, the response of two lettuce varieties Verte and Romaine to isoosmotic NaCl and Na 2 SO 4 treatments were examined. Both varieties were grown in pots containing nutrient Hoagland solution with or without 100 mM NaCl or 77 mM Na 2 SO 4 . Relative growth rate (RGR), hydraulic parameters, root ion content, proline and several antioxidant activities in roots were measured after 12 days of treatment. After prolonged exposure to salt stress, relative growth rate and water content of lettuce significantly decreased. Roots accumulated high level of Na + under both salts, whereas the accumulation of K + and Ca 2+ decreased. High level of Na + inside the cells inhibited the K + uptake and resulted in increased K + /Na + ratio. In addition, salt stress also caused an increase in the accumulation of proline. This result suggests that proline may play a crucial role in protecting lettuce under salt stress especially in response to Na 2 SO 4 treatment. Membrane damage estimated by electrolyte leakage (EL) increased especially in response to Na 2 SO 4 treatment in both varieties, but Verte had significantly lower EL relative to Romaine under 100 mM NaCl. A reduction in the activities of CAT in both varieties under 100 mM, and GPX activity in Verte under Na 2 SO 4 treatment coincided with an increase in H 2 O 2 level, indicative of cellular damage and a general depression of the antioxidant enzymatic system in lettuce roots. Keywords: Lettuce, NaCl, Na 2 SO 4 , RGR, mineral nutrition, antioxidant activities, proline