Abstract
The germination and development of several plant species can be limited when those plants are grown in soils with high salinity, which reduces seedling viability and vigor, as well as activating the antioxidant defense system. The aim of this study was to evaluate germination, initial growth and activity of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) in seedlings of three onion cultivars (Madrugada, Fepagro 27 and Petroline) exposed to different concentrations of NaCl (0, 40, 80, 120 and 160 mM). Seedlings were evaluated for viability, vigor and antioxidant enzyme activity. The experimental procedures were completely randomized in 3 × 5 factorial design, with each treatment performed in triplicate, at a significance level of 5%. For all cultivars, viability and vigor decreased in parallel with increasing NaCl concentrations, whereas antioxidant enzyme activity increased, and one cultivar (Madrugada) showed less salt tolerance than did the others. We conclude that high NaCl concentrations have a negative effect in the physiological quality of onion seeds, resulting in lower seedling growth rates and increased antioxidant enzyme activity, where Fepagro 27 and Petroline cultivars were more tolerant to salt stress than 'Madrugada'.
Highlights
The salinization of soils dedicated to agriculture, caused by the accumulation of salts in irrigation water, causes these soils to become increasingly unproductive (Lima & Bull 2008)
In addition to the growth characteristics, we evaluated the activities of the antioxidant enzymes superoxide dismutase (SOD) (EC 1.15.1.1), ascorbate peroxidase (APX) (EC 1.11.1.11) and CAT (EC 1.11.1.6) in a spectrophotometer (Ultrospec 2100 pro UV/visible; Amersham Biosciences, Piscataway, NJ, USA), in order to determine the antioxidant metabolism of onion seedlings subjected to salt stress
The germinability of the seeds of the onion cultivars subjected to salt stress was affected by the increase in NaCl concentration
Summary
The salinization of soils dedicated to agriculture, caused by the accumulation of salts in irrigation water, causes these soils to become increasingly unproductive (Lima & Bull 2008). When irrigation waters have a high concentration of salts and there is no possibility of exporting these brackish waters to a sink, they can accumulate and cause damage (Santos et al 2009). Such accumulation can limit the germination and development of various species (Barroso et al 2010), leading to morphological, cellular, biochemical and molecular alterations that hinder the agricultural yield in response to the decrease in the water potential of the soil solution induced by the high osmolarity (Lima & Bull 2008). Salt stress can lead to excess intracellular production of reactive oxygen species (ROS) such as the superoxide radical (O2−), the hydroxyl radical (OH−), hydrogen peroxide (H2O2), and singlet oxygen (1O2) (Stanisavljević et al 2011)
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