Evaluation of some morphological and biochemical traits and antioxidant enzymes activity in Iranian native turnips under salinity stress caused by sodium chloride

Salinity is a multidimensional stress affecting crop yield and productivity at various levels of plant organization. The plant response to salinity consists of numerous processes that must function in coordination to alleviate both cellular hyper osmolarity and ion disequilibrium. In addition, crop plants must be capable of satisfactory biomass production in a saline environment (yield stability). Excess of salt concentrations causes enhanced generation of reactive oxygen species (ROS) in plants. In contrast, plants are equipped with a diverse array of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POX) and polyphenol oxidase (PPO) against oxidative damages by reactive oxygen species. Turnip (Brassica rapa L. subsp. Rapifera) as a source of strong health food, contain a variety of antioxidants and Iran is one of the main centers of diversity. Indigenous accessions has a set of morphological, physiological and phenologycal that increase water use efficiency in the soil in saline and dry environments. Study of physiological and biochemical changes made in understanding the mechanisms of resistance to salinity stress conditions and access to genetic resources for breeding programs is essential. According to the limited information available in the field of physiological and biochemical reactions turnip cultivars to salinity, especially in indigenous accessions, in order to determine the response of morphological, biochemical and enzymatic turnip indigenous masses to salinity, the research carried out was.
This study aimed to assess the response of Iranian indigenous turnip accessions to salinity stress in terms of biochemical traits and antioxidant enzymes activity, to further understanding of salinity resistance mechanisms in plants and access to better genetic resources. The indigenous turnip accessions including Ardakan, Shiraz and Kermanshah evaluated at four levels of soil salinity (0, 60, 120 and 180 mM) as factorial experiment in a completely randomized design with three replications at Yazd Agricultural and Natural Resources Research Center, during 2013. Twenty days after the first germination as salinity treatments were done gradually. Eight weeks after salt treatment, the sampling for biochemical traits (proline, total phenols, malondialdehyde, catalase and superoxide dismutase) from the youngest mature leaves were separated from each other and then shoot and root traits morphology (root and shoot dry weight) were measured. SAS data analysis was used to compare the means and the Duncan´s (P ≤ 0.5) test.
The results showed that morphological traits such as shoot and root biomass, were mainly affected by severe salinity stress, but salinity stress (120 and 180 mM) had no significant effect on these traits. In this study, increased salinity stress increases the leaf proline and malondialdehyde content and reduced total phenolic in all accessions. The highest proline obtained in sensitive indigenous accessions (kermanshah) at severe salinity stress. Enzymes activity of superoxide dismutase and catalase increased in salinity resistant accession kermanshah than other accessions. Existence or poor performance of salinity tolerance or avoidance mechanisms in kermanshah accession possibly caused induction of oxidative stress and produced antioxidant enzymes. In terms of salinity, plant to reduce the effects of oxidative stress antioxidant enzymes such as superoxide dismutase and catalase activity increases. The activity of the enzyme superoxide dismutase and catalase negative correlation with leaf malondialdehyde (-0.88**,-0.91**) there. Also, a significant positive correlation (0.9**) between activity of catalase and superoxide dismutase indicates a close relationship between these two enzymes in removing free radicals.
Shoot and root biomass were mainly affected by high salt stress and accession Ardakan shoot biomass was highest, maybe the accessions to fight the salinity of sodium and chloride ions into the cell vacuole leaves the store. In this study, increase of salinity, proline and malondialdehyde increased in all accessions. Accession kermanshah were the most proline in extreme conditions of salinity, which indicates the ability of the accessions to accumulate proline, malondialdehyde and other organic solute to prevent oxidative stress and maintain inflammation plant cells. The effect of salinity stress, superoxide dismutase and catalase enzyme activity were sustained in the accession production of these enzymes, a sign of oxidative stress caused by salinity.