Effectiveness of Gamma Irradiated Protoplasts on Improving Salt Tolerance of Lemon (Citrus limon L. Burm.f.)

Evaluating the role of gamma irradiation to ameliorate salt stress in corn

PURPOSE

Salt stress is a significant issue in corn cultivation leading to corn yield reduction, especially in the arid and semi-arid regions. Nuclear technologies, along with other standard methods, can be used as an efficient method for mitigating salt stress effects on plants.

MATERIALS AND METHODS

In this research, gamma irradiation (GI) was studied on seeds in the salt stress amelioration of corn in laboratory and field conditions. A total of five doses of gamma rays (25, 50, 100, 150 and 200 Gy) were applied to corn seeds (SC.703) at the laboratory under saline and control conditions. The best gamma-ray treatment (25 Gy) was selected for studying corn under salt stress in the field condition.

RESULTS

The length of the radicle, seminal roots and shoot, dry weight of radicle, and seminal roots were affected by salt stress (p <.001). However, GI affected only the radicle and seminal root length (p < .001). The radicle length was decreased as much as 3, 11, 17, 25, and 27% in 25, 50, 100, 150 and 200 Gy of GI, respectively. In addition, the seminal root length was decreased in all GI treatments except 25 Gy (p < .05). Plants derived from seeds exposed to GI (25 Gy) had a higher chlorophyll content of 1, 17, and 29% at V3 (third leaf stage), R1 (silk stage, p < .001), and R4 (dough stage, p < .001), respectively. In GI treatment, the soluble carbohydrate content was significantly higher (p < .001) at all three measurement stages and the soluble protein was significantly higher (p < .001) only at the R4 stage. Moreover, proline content was higher in GI (25 Gy) at V3 (58%, p < .05) and R1 (98%, p < .001) treatment stages.

CONCLUSION

Since plants from gamma-irradiated seeds had a greater plant weight and their economic traits (cob and grain weight) were higher compared to control plants under salt stress conditions, it can be concluded that a low dose of GI may ameliorate the effect of salt stress on the corn plants.

Application of gamma rays on salinity tolerance of wheat (Triticum aestivum L.) and expression of genes related to biosynthesis of proline, glycine betaine and antioxidant enzymes

We investigated the effects of salinity stress and gamma radiation on salinity tolerance in wheat crops. To this end, mutant lines were generated by exposing Arg and Bam wheat varieties at the primordial state to 150 and 200 gamma radiation doses in the field. The top 15 mutant lines were specified for cultivation in the fifth-generation under two conditions, including non-stress and salinity stress. According to Fernandez's model, the three mutant lines had high yields under both conditions. The three mutant lines were selected with their two parents, and then, cultivated in a completely randomized factorial design in a greenhouse under non-stress and salinity conditions. The mutant lines showed significantly higher osmotic adjustment, leaf relative water content (RWC), potassium ion concentration, soluble sugar content and lower proline (Pro), and glycine betaine (GB) content than the parents at both the vegetative (VEG) and reproductive (REP) stages under salinity conditions. The expression of genes involved in the Pro biosynthesis pathway, P5CS and P5CR genes, in mutant lines were less than their parents, and conversely, P5CDH in mutant lines was more than their parents. The changes in the expression of CMO and BADH genes involved in the GB synthesis pathway indicated that the mutant lines had less gene expression compared to their parent genotypes of Arg and Bam. The results indicated an increase in antioxidant activity in the mutant lines compared to their parents. Consequently, irradiated plants have probably adapted to the salinity stress by increasing the osmotic adjustment, RWC, potassium ion concentration, and soluble sugar content, as well as activating antioxidant enzymes.

Impact of gamma irradiation pretreatment on the growth of common vetch (Vicia sativa L.) seedlings grown under salt and drought stress

It has been generally accepted that the morphology, physiology and biochemistry of plants are differentially affected by low-dose gamma ionizing radiation that is associated with the tolerance of plant species under biotic/abiotic stress. Therefore, the aim of this study is to investigate the protective role of low gamma irradiation pretreatment against salt and drought stress. For this aim, irradiated (100 Gy) and non-irradiated seeds of common vetch were cultured on an MS medium with separate addition of concentrations of NaCl (100 mM) and PEG-6000 (100 g/l) under in vitro conditions. Morpho-physio-biochemical analyses were carried out on 14-day-old seedlings. The findings of this study clearly show that exposure to gamma irradiation pretreatment (100 Gy), alone or in combination with salt stress and drought stress, led to significant increases (p < .01) in dry matter accumulation, CAT, SOD and APX activities, proline contents and decreases in relative water content. However, alone, gamma irradiation pretreatment caused increased chlorophyll contents while decreasing MDA contents. Overall, these results suggested that low-dose gamma irradiation pretreatment can enhance the tolerance of common vetch seedlings against stress due to salt and drought.

Pretreatment with High-Dose Gamma Irradiation on Seeds Enhances the Tolerance of Sweet Osmanthus Seedlings to Salinity Stress

The landscape application of sweet osmanthus (Osmanthus fragrans) with flower fragrance and high ornamental value is severely limited by salinity stress. Gamma irradiation applied to seeds enhanced their tolerance to salinity stress as reported in other plants. In this study, O. fragrans ‘Huangchuang Jingui’ seeds were pretreated with different doses of gamma irradiation, and tolerance of the seedlings germinated from the irradiated seeds to salinity stress and the changes of reactive oxygen species (ROS) production and ROS scavenging systems induced by gamma irradiation were observed. The results showed that seed pretreatment with different doses of gamma irradiation enhanced the tolerance of sweet osmanthus seedlings to salinity stress, and the positive effect induced by gamma irradiation was more remarkable with the increase of radiation dose (50–150 Gy). The pretreatment with high-dose irradiation decreased O2− production under salinity stress and mitigated the oxidative damage marked by a lower malondialdehyde (MDA) level, which could be related to the significant increase of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in the seedlings germinated from the irradiated seeds compared to the corresponding control seedlings. In addition, the accumulation of proline in the irradiated seedlings may contribute to enhancing their tolerance to salt stress by the osmotic adjustment. The study demonstrated the importance of regulating plant ROS balance under salt stress and provided a potential approach to improve the tolerance of sweet osmanthus to salt stress.

Silybin content and overexpression of chalcone synthase genes in Silybum marianum L. plants under abiotic elicitation

Silymarin, a Silybum marianum seed extract containing a mixture of flavonolignans including silybin, is being used as an antihepatotoxic therapy for liver diseases. In this study, the enhancing effect of gamma irradiation on plant growth parameters of S. marianum under salt stress was investigated. The effect of gamma irradiation, either as a single elicitor or coupled with salinity, on chalcone synthase (CHS) gene expression and silybin A + B yield was also evaluated. The silybin A + B content in S. marianum fruits was estimated by liquid chromatography-mass spectrometry (LC-MS/MS). An increase in silybin content was accompanied by up-regulation of the CHS1, CHS2 and CHS3 genes, which are involved in the silybin biosynthetic pathway. The highest silybin A + B production (0.77 g/100 g plant DW) and transcript levels of the three studied genes (100.2-, 91.9-, and 24.3-fold increase, respectively) were obtained with 100GY gamma irradiation and 4000 ppm salty water. The CHS2 and CHS3 genes were partially sequenced and submitted to the NCBI database under the accession numbers KT252908.1 and KT252909.1, respectively. Developing new approaches to stimulate silybin biosynthetic pathways could be a useful tool to potentiate the use of plants as renewable resources of medicinal compounds.

Evaluation of Antioxidant and Antibacterial Potentials of Nigella sativa L. Suspension Cultures under Elicitation

Nigella sativa L. (family Ranunculaceae) is an annual herb of immense medicinal properties because of its major active components (i.e., thymoquinone (TQ), thymohydroquinone (THQ), and thymol (THY)). Plant tissue culture techniques like elicitation, Agrobacterium mediated transformation, hairy root culture, and so on, are applied for substantial metabolite production. This study enumerates the antibacterial and antioxidant potentials of N. sativa epicotyl suspension cultures under biotic and abiotic elicitation along with concentration optimization of the elicitors for enhanced TQ and THY production. Cultures under different concentrations of pectin and manganese chloride (MnCl₂) elicitation (i.e., 5 mg/L, 10 mg/L, and 15 mg/L) showed that the control, MnCl₂ 10 mg/L, and pectin 15 mg/L suspension extracts greatly inhibited the growth of E. coli, S. typhimurium, and S. aureus (MIC against E. coli, i.e., 2.35 ± 0.8, 2.4 ± 0.2, and 2.46 ± 0.5, resp.). Elicitation decreased SOD enzyme activity whereas CAT enzyme activity increased remarkably under MnCl₂ elicitation. MnCl₂ 10 mg/L and pectin 15 mg/L elicitation enhanced the DPPH radical inhibition ability, but ferric scavenging activity was comparable to the control. TQ and THY were quantified by LC-MS/MS in the cultures with high bioactive properties revealing maximum content under MnCl₂ 10 mg/L elicitation. Therefore, MnCl₂ elicitation can be undertaken on large scale for sustainable metabolite production.

Effect of gamma irradiation on antioxidant properties of ber (Zizyphus mauritiana) fruit

Effect of gamma irradiation (0.25 to 1.0kGy) on antioxidant properties of ber fruit was studied. Antioxidant properties of ber fruits were determined by Scavenging DPPH radical activity, reducing power assay, super oxide anion radical activity, TBARS, total phenolic content and total flavonoid content. Gamma irradiation treatment up to 1.0kGy elevated the Scavenging DPPH radical activity (9 %), super oxide anion radical activity (26 %) and total flavonoid content (208 %) compared to fresh ber fruit. On the other hand it brought down the reducing power activity (65 %) and total phenolic content (18 %) as compared to raw fruit. The TBARS activity statistically increased upon irradiation of ber fruit. It indicated that total antioxidant activity decreased as TBARS value increased. Therefore 0.25 to 0.5kGy is better dose to retain the natural antioxidant in fruit.

Physiological and molecular characterization of the enhanced salt tolerance induced by low-dose gamma irradiation in Arabidopsis seedlings

It has been established that gamma rays at low doses stimulate the tolerance to salt stress in plants. However, our knowledge regarding the molecular mechanism underlying the enhanced salt tolerance remains limited. In this study, we found that 50-Gy gamma irradiation presented maximal beneficial effects on germination index and root length in response to salt stress in Arabidopsis seedlings. The contents of H2O2 and MDA in irradiated seedlings under salt stress were significantly lower than those of controls. The activities of antioxidant enzymes and proline levels in the irradiated seedlings were markedly increased compared with the controls. Furthermore, transcriptional expression analysis of selected genes revealed that some components of salt stress signaling pathways were stimulated by low-dose gamma irradiation under salt stress. Our results suggest that gamma irradiation at low doses alleviates the salt stress probably by modulating the physiological responses as well as stimulating the stress signal transduction in Arabidopsis seedlings.