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Nitrogen (N) acts as nutrient and signaling molecule in plants all over their development stages. The involvement of various N forms in the regulation of seed germination response to salt stress was assessed in the present work. Nitrogen sources (NO, NO2 , NO3 , NH4 +, glutamine and glutamate) were added at 1mMto the germination medium of barley (Hordeum vulgare, cv Ardhaoui) in combination or not with NaCl stress (14 g.L−1). The application of nitrogen monoxide (NO) alleviated by about 20% the NaCl-induced germination capacity decrease. However, the addition of ammonium ions (NH4 +) and glutamic acid (Glu) accentuated the inhibitory effects of NaCl, decreasing germination capacity by about 50% compared to the control. The levels of malondialdehyde (MDA), which is an indicator of membrane lipid peroxidation by stresses, were increased by salinity in seeds treated with nitrite (NO2 ), NO3 , Glu and Gln. In N-free medium, NaCl stress induced a severe nitrate reductase activity (NR, EC 1.6.1.6) inhibition. Such an effect was alleviated by the application of N treatments. Glutamate dehydrogenase (GDH, EC 1.4.1.2) aminating activity (NADH-GDH) of seedlings was inhibited by NaCl stress in the presence of NO, Glu and Gln. Conversely, there was stimulation by salt stress of NADH-GDH activity in seedlings treated with NaCl and NH4 +. Deaminating GDH activity (NAD-GDH) was found to be enhanced by salt stress in NO2 and NO3 treatments. The differential effects of applied N forms on germination and early seedling development processes in this grass probably underlines different regulatory actions within N mobilization and assimilation.

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Interaction of salinity, nitrate, light, and seed weight on the germination of Crithmum maritimum was investigated. Seeds of three size categories were germinated at 0–200 mM NaCl with either 0, 5 or 20 mM KNO 3 . Experiments were done under darkness, white light, or red light. Regardless of seed weight, germination was maximal in distilled water. Under salinity, the smallest seeds showed the highest germination percentage. Salt impact was amplified by darkness, but was mitigated by nitrate supply, red light and their combination. At the same PPFD, germination of T2 seeds was higher, when exposed to red light than under white light, suggesting that germination was more influenced by the light type than by the PPFD. As a whole, not only salinity, nutrient availability, seed weight, and light, but also their interaction may control the germination of this halophyte.

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Acta Biologica Hungarica
Authors:
Najoua Karray-Bouraoui
,
Houneida Attia
,
Manel Maghzaoui
,
Najoua Msilini
,
M. Rabhi
, and
M. Lachaâl

Physiological responses of Arabidopsis thaliana to the interaction of iron deficiency and nitrogen form were studied using plants grown in hydroponics. Thirty-three-day-old seedlings were submitted to four treatments for 7 days: NO 3 + 5 μM Fe; NO 3 + 0.1 μM Fe; NH 4 + 5 μM Fe and NH 4 + 0.1 μM Fe. Leaf growth and chlorophyll content were highest in NO 3 -fed, Fe sufficient plants, but were strongly diminished by Fe deficiency under nitric nutrition, and by ammoniacal nutrition independently of Fe regime. However, the leaves of NH 4 -fed plants presented a higher Fe content than those of Fe sufficient, NO 3 -fed plants. Thus, leaf chlorosis of NH 4 -fed in plant did not depend on Fe availability, and seemed to be due to another factor. Root acidification capacity and Fe-chelate reductase (FCR) activity were also dependent on N form. The medium was acidified under ammoniacal regime and alkalinized under nitric regime regardless of Fe level. FCR activity stimulation in response to Fe deficiency was observed only in NO 3− fed plants. In addition, both N form and Fe level induced antioxidant responses in rosette leaves. Ammoniacal regime increased both peroxidase expression and anthocyanin accumulation, whereas Fe deficiency enhanced superoxide dismutase expression.

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Cotula coronopifolia is a wild annual Asteraceae that grows in periodically-flooded prone environments and seems highly tolerant to periodic flooding. Seedlings of about 15 cm were collected directly from the edge of Soliman sabkha (N-E Tunisia, semi-arid stage) and grown under greenhouse conditions. Two treatments were considered: drainage and flooding. After 56 days of treatment, flooded plants showed a pronounced growth increase. This performance was essentially associated with significant increment in biomass production of both shoots and roots (about 220% of the control). The appropriate response to flooding was also characterized by the ability of the species to maintain its water status under such conditions. Neither water content nor water potential showed a significant variation as compared to those of non-flooded plants. However, transpiration rate decreased slightly but significantly in flooded plants (from 0.86 to 0.64 mmol H2O m−2 s−1). Na+ and K+ concentrations were practically maintained under waterlogging conditions, except a significant increase of Na+ content in roots of flooded plants (157% of the control). These responses were concomitant with maintenance of photosynthetic rate. However, the contents of chlorophylls a and b increased to 167% and 295%, respectively. It seems that the enhancement in these photosynthetic pigments together with a significant improvement in water use efficiency (from 4.66 to 6.07 mmol CO2 mol−1 H2O) allowed to the species to compensate the decrease in photosynthetic rate. At the anatomical level, this species responded to flooding by a significant development of its root aerenchyma (+63%) and an increase in the lignification of its stem xylem tissues (+37%). Based on the presented data, the plant fitness under flooding conditions was a result of dynamic readjustment of several morphological, physiological, and anatomical adaptive traits. Flood requirement together with salt tolerance are responsible for the predominance of C. coronopifolia in a large area in its natural biotope where most plants cannot tolerate interactive effects of flooding and salinity.

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Acta Biologica Hungarica
Authors:
M. Rabhi
,
S. Hajji
,
Najoua Karray-Bouraoui
,
Deborah Giuntini
,
Antonella Castagna
,
A. Smaoui
,
Annamaria Ranieri
, and
C. Abdelly

In the present investigation, we studied uptake and management of the major cations in the xerohalophyte, Tecticornia indica (Willd.) subsp. indica as subjected to salinity. Plants were grown under greenhouse conditions at various salinity levels (0, 100, 200 and 400 mM NaCl) over 110 days. At harvest, they were separated into shoots and roots then analyzed for water contents, dry weights (DW), and Na+, K+, Ca2+, and Mg2+ contents. Plants showed a growth optimum at 200 mM NaCl and much better tissue hydration under saline than non-saline conditions. At this salt concentration (200 mM NaCl), shoot Na+ content reached its highest value (7.9 mmol · g−1 DW). In spite of such stressful conditions, salt-treated plants maintained adequate K+, Ca2+, and Mg2+ status even under severe saline conditions. This was mainly due to their aptitude to selectively acquire these essential cations and efficiently use them for biomass production.

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