Physiological property and yield of the sweet sorghum mutants induced by heavy ion irradiation

Physiological property and yield of the sweet sorghum mutants induced by heavy ion irradiation 1 first-author 1 1 1 1 1 corresp Corresponding author. E-mail address: dongxicun@impcas.ac.cn Corresponding author. E-mail address: dongxicun@impcas.ac.cn dongxicun@impcas.ac.cn Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China Soil salinity can limit plant growth and productivity. The cultivation of tolerant varieties is convenient and cost-effective for making good use of the saline soils. The sweet sorghum plant has a high tolerance for saline alkaline soils. The KF1210-3 and KF1210-4 early-maturity mutants of sweet sorghum were obtained via carbon ion irradiation. The study assesses the productivity of three sweet sorghum cultivars (KF1210-3, KF1210-4, and KFJT-CK) which were grown in intermediate (4.6 dSm −1 ) and high (11.9 dSm −1 ) soil salinity. The sweet sorghum grown in the soil salinity of 4.6 dSm −1 produced 50.00–57.30% greater fresh weight than that in the soil salinity of 11.9 dSm −1 , while the difference was not as obvious among the dry biomass of the three sweet sorghum cultivars. Moreover, the Brix degree of the sweet sorghum grown in the soil salinity of 11.9 dSm −1 was greater than that grown in the soil salinity of 4.6 dSm −1 . The heavy ion irradiation experiment is of great significance in screening plant mutants, improving environmental conditions, and assessing the productivity. This process, in turn, aids in the understanding of the effects of the biochemical and physiological mechanisms of salt stress. Heavy ion irradiation Sweet sorghum Salinity K/Na ratio 1. Introduction 1 Soil salinity is a serious abiotic stressor that can limit plant growth, productivity, and distribution in agricultural contexts [ 1 1 - 3 3 1-3 ], especially in countries where irrigation is an essential aid to agriculture. Saline soils have been estimated to account for approximately 10-20% of global arable land, and the problem of secondary salinization is becoming even more serious due to high levels of evapotranspiration and improper water management. Therefore, the cultivation of tolerant species is an effective method of effectively utilizing saline soils. Sweet sorghum is a C 4 crop in the grass family, which also includes grain and fiber sorghum. Sweet sorghum grows in marginal areas due to its high tolerance to saline and drought conditions [ 4 4 , 5 5 ]. This forage crop is widely used due to its high yield, nutritional quality, high sugar content, and digestible materials. In addition, sweet sorghum has often been used to improve soil organic fertility and nitrogen economy [ 6 6 ]. The studies on sweet sorghum salt tolerance are scarce and controversial, which necessitates additional research to explore more tolerant varieties and their mechanism of salt tolerance [ 3 3 , 7 7 ]. Therefore, we can screen novel varieties to enhance the amount of quality raw materials that can be produced from the sweet sorghum. It has been reported that sorghum exhibits large genotypic variations for salinity tolerance [ 8 8 ]. The traditional hybridization-based breeding is inefficient due to the lack of genetic resources and the long breeding cycle. However, the use of heavy ion irradiation is an effective method to generate plant mutants. The use of nuclear techniques in plant breeding has been widely implemented for inducing mutations [ 9 9 , 10 10 ]. In comparison to low linear energy transfer (LET) radiation (such as electrons, X-rays, and gamma rays), heavy ion irradiation, predominantly present in space, is characterized by a high linear energy transfer (LET) and relative biological effectiveness (RBE). These features of LET are expected to increase mutation frequency and mutation spectrum. Ionizing radiation can cause DNA damage, which can lead to a higher fraction of DNA breaks. The mere presence of different cultivars, genotypes, and ecotypes of sweet sorghum is a valuable source for screening and identifying types tolerant to salinity stress [ 11 11 , 12 12 ]. In this study, sweet sorghum mutants are generated via heavy ion irradiation. The early maturity mutants KF1210-3 and KF1210-4 were screened and then grown in intermediate (4.6 dSm −1 ) and high (11.9 dSm −1 ) soil salinity. The - osmotic stress and ionic stress responses of the sweet sorghum mutants in saline conditions are investigated, which is an important issue that needs to be clarified. It is well known that the high salinity levels in the external media could affect many physiological and metabolic processes, leading to low cell growth and development [ 13 13 ]. Under these conditions, different biochemical and physiological responses are induced to help the plants to survive. Therefore, selecting tolerant cultivars, improving environmental conditions, and assessing the productivity are essential for understanding the effects of the biochemical and physiological mechanisms of salt stress. 2. Methods and Materials 1 2.1. Plant and irradiation 2 The sweet sorghum seeds, Sorghum bicolor (L.) Moench “KFJT-CK,” were provided by the Institute of Modern Physics of the Chinese Academy of Sciences. Dry seeds of equal size without mold or lesions were selected. The carbon ions were generated by the Heavy Ion Research Facility in Lanzhou (HIRFL) facility, Institute of Modern Physics, CAS (IMP). The energy of the carbon ions was 100 MeV/u, and the dose rate was approximately 20 Gy/min. The dry seeds were irradiated by the carbon ions with the doses of 0, 20, 40, 60, and 80 Gy. The early maturity mutants (KF1210-3 and KF1210-4) were screened with the irradiation dose of 80 Gy and bred for further experiments. 2.2 Soil sampling and assays 2 After the establishment of the plots and before sowing the sweet sorghum (i.e., initial soil condition before the implementation of the treatments), composite soil samples were collected from each experimental plot at 0–20 cm depths. Soil sampling was also undertaken after the harvest of sweet sorghum in each cropping year. The collected samples were processed (air-dried, ground to pass through a 2 mm sieve, and mixed thoroughly) before being subjected to the following soil analyses: salinity, pH, sodium (Na + ), and potassium (K + ) via flame photometry. All methods were according to those described by the U.S. Salinity Laboratory Staff. Sodium adsorption ratio (SAR) was calculated via concentrations of Na + from the saturation paste extract. The experimental results are shown in Table 1 Table 1 . The means followed by the same letter within each salinity or cultivar effect are not significantly different according to the Fisher’s protected the Least Significant Difference (LSD) test at P = 0.05. 1 1 Salinity ( dS  m −1 ) 1 1 Cultivar 1 1 Fresh biomass(t ha −1 ) 1 1 Dry biomass(t ha −1 ) 1 1 Brix degree(%) 1 3 4.6 1 1 KFJT-CK 1 1 66.52b 1 1 26.36b 1 1 14.68a 1 1 KFJT-1210-3 1 1 65.49b 1 1 25.21b 1 1 20.37b 1 1 KFJT-1210-4 1 1 55.64b 1 1 18.89a 1 1 21.09b 1 3 11.9 1 1 KFJT-CK 1 1 43.33a 1 1 14.89a 1 1 15.08a 1 1 KFJT-1210-3 1 1 41.85a 1 1 14.32a 1 1 22.50b 1 1 KFJT-1210-4 1 1 37.22a 1 1 13.08a 1 1 22.49b 2.3 Treatments and experimental design 2 The experiment was established in the industrial park of Wuwei in China (approximately 20 hm 2 ), which exhibits great variability in soil salinity. The sweet sorghum seeds that had been irradiated by carbon ions were sown in the field on April 26, 2014. The sweet sorghum was harvested on October 2, 2014. The soil salinity was within the range of 3.2 dSm −1 -12.6 dSm −1 , and the soil pH was approximately 8.5. Each treatment was replicated three times according to a randomized block design. A plot size of 240 m 2 was adopted. The space between rows was 50 cm, and plants were spaced 20 cm apart within a row. This spacing conforms to typical sweet sorghum protection and irrigation practices [ 14 14 ]. In the experimental field, the two saline soil blocks (80 m x 34 m; 2720 m 2 ) were selected on the basis of their salinity level (4.6 dSm −1 and 11.9 dSm −1 ). The two salinity blocks (part 1 and part 2) were separated by a wide alley (50 m) to maintain the integrity of each salinity level. The three sweet sorghum cultivars (KF1210-3, KF1210-4, and KFJT-CK) were planted in rows (20 cm) by hand in the block design to achieve an approximate density of 500,000 seeds ha −1 . Before sorghum planting, 260 kg N ha −1 as ammonium sulphate ((NH 4 ) 2 SO 4 ), 100 kg P ha −1 as super phosphate (Ca(H 2 PO 4 ) 2 ), and 195 kg K ha −1 as potassium sulphate (K 2 SO 4 ) were applied and incorporated into the soil of all experimental plots. After planting, all experimental plots were irrigated with 30 mm of water for the emergence of the sweet sorghum. The salinity of water used for irrigation was lower than 1.0 dSm −1 to avoid additional adverse effects, especially on the sweet sorghum biomass. The growth-stage irrigation began in early July and was sustained until harvest. During this period, the entire area was irrigated four times with 120 mm of water. The barnyard grass was hand-removed. Other agricultural practices were carried out according to the recommended production practices for sorghum fields in China. 2.4 Measurement of agronomic characters 2 The fresh biomass of the sweet sorghum was determined by hand-harvesting at the hard dough stage of each sorghum cultivar, which was approximately 35 days after blossom. The sweet sorghum provides the greatest biomass and total sugar yield at this stage. Ten randomly selected plants were chopped into 1 cm long pieces, and 4 kg of chopped biomass samples was used for determination of dry biomass yields. The Brix degree of the sweet sorghum juice was measured with an automatic lab refractometer (Model ATR-ST, Topac, MA, USA). 2.5 Physiological assays 2 The chlorophyll content was determined from the same leaf samples used for the reflectance measurement. The method of measurement was conducted according to Lichtenthaler [ 15 15 ]. The proline content was estimated using the acid-ninhydrin method [ 16 16 ]. Ten stems and ten roots from the five marked plants of each plot were collected for determination of the Na + and K + ratio at the physiological maturity stage. The samples were dried at 65 °C for 72 h and were then ground in a Wiley mill to pass through a 1 mm screen. The sodium ions (Na + ) and potassium ions (K + ) in the roots and stems were determined via an atomic absorption spectrophotometer (AA, Model M6, Thermo Elemental, MA, USA) [ 17 17 ]. In addition, the K + /Na + ratio was calculated and used for further data analysis. 2.6 Statistical analysis 2 Statistical analysis was performed using the Statistical Analysis System (SAS) computer program. The means were compared according to the Duncan multiple range test. 3. Results and Discussion 1 3.1. The emergence and yields of the sweet sorghum 2 In particular, the plant density of the sweet sorghum in the soil salinity of 11.9 dSm −1 was 37% lower (43,614 plants ha −1 ) than that in the soil salinity of 4.6 dSm −1 (69,275 plants ha −1 ). Averaged across the two soil salinity levels, the KFJT-CK sweet sorghum cultivar (47.753 plants ha −1 ) was seriously affected by the soil salinity. The KF1210-3 and KF1210-4 sweet sorghum showed greater levels of emergence (56,467 plants ha −1 and 53, 564 plants ha −1 , respectively). The effects of soil salinity and cultivar on fresh biomass, dry biomass, and the Brix degree of the sweet sorghum juice are shown in Table 2 Table 2 . The fresh biomass of the KFJT-CK, KF1210-3, and KF1210-4 sweet sorghum cultivars ranged from 43.33 t ha −1 to 66.52 t ha −1 , 41.85 t ha −1 to 65.49 t ha −1 , and 37.22 t ha −1 to 55.64 t ha −1 in the different salinity conditions (11.9 dSm −1 to 4.6 dSm −1 ), respectively. The dry biomass of the KFJT-CK, KF1210-3, and KF1210-4 sweet sorghum cultivars ranged from 14.89 t ha −1 to 26.36 t ha −1 , 14.32 t ha −1 to 25.21 t ha −1 , and 13.08 t ha −1 to 18.89 t ha −1 , respectively. By comparing the three sweet sorghum cultivars under conditions of increasing soil salinity, it was found that the fresh biomass of sweet sorghum was reduced with increasing soil salinity. However, the results did not show significant differences in dry biomass between salinity treatments. In addition, the Brix degree values of the KFJT-CK, KF1210-3, and KF1210-4 sweet sorghum cultivars ranged from 14.68% to 15.08%, 20.37% to 22.50%, and 21.09% to 22.49% with the increasing salinity. Netondo et al. found that when the external NaCl concentration increased during the sensitive vegetative phases, both the sorghum leaf growth and leaf area decreased. This led to lower biomass production [ 18 18 ]. The means followed by the same letter within each factor and sorghum growth stage are not significantly different according to the Fisher’s protected LSD test at P = 0.05. 1 1 Time 1 1 pH 1 1 Organic matter(g/kg) 1 1 Salinity( dS  m −1 ) 1 1 Na + (mg/kg) 1 1 K + (mg/kg) 1 1 Pre-planting 1 1 8.18a 1 1 17.833a 1 1 4.6a 1 1 22.74a 1 1 23.23a 1 1   1 1 8.76a 1 1 14.642a 1 1 11.9c 1 1 29.84b 1 1 27.93a 1 1 Mature period 1 1 8.05a 1 1 24.854b 1 1 3.8a 1 1 16.09a 1 1 38.45a 1 1   1 1 8.45a 1 1 22.472a 1 1 8.7b 1 1 20.28a 1 1 30.27a 3.2. Physiological parameters 2 In plants, chlorophyll a can capture photons that are scarcely absorbed by chlorophyll b in photosynthetic light-harvesting complexes. In most cases, the increasing soil salinity caused a decrease in the total plant chlorophyll. In this experiment, the chlorophyll content index (CCI) of sweet sorghum in the bloom growth stages was affected by the soil salinity and sorghum cultivar type. The increase in soil salinity decreased the sweet sorghum CCI from 8% to 15% ( Fig. 1 Fig. 1 ). This result may be related to the mechanism of salt tolerance in sweet sorghum, and it may aid in screening for tolerant sweet sorghum cultivars. Under greenhouse conditions, Netondo et al. found that the sorghum Chlorophyll a and Chlorophyll b are reduced from 58% to 70%, while the net CO 2 uptake is almost completely inhibited when the external NaCl concentration increased to 200 mM [ 19 19 ]. Proline is a solute that helps regulate cellular osmolarity during stress in plants, and it is an effective cryoprotectant against natural stresses [ 20 20 , 21 21 ]. Under salt stress conditions, tolerant sweet sorghum cultivars can accumulate proline to prevent changes in plasma membrane permeability as well as protect the integrity and stability of the plasma membrane proteins. At the same time, the sweet sorghum can maintain high osmotic pressure stress to absorbed moisture under salt stress. In Fig. 2 Fig. 2 , the proline content exhibits little change between the sorghum cultivars in the soil salinity of 4.6 dSm −1 . In contrast, proline content of KF1210-3 and KFJ1210-4 are higher than KFJT-CK in the soil salinity of 11.9 dSm −1 . The proline content of KFJT-1210-3 was increased by 36.94% compared to KFJT-CK. The result indicates that KF1210-3 has the strongest resistance to the salt stress. Carbon ion irradiation may change a key gene of the proline metabolic pathway of sweet sorghum. Blum and Ebercon also suggested that proline has an active role in recovery metabolism [ 22 22 ]. Liu et al. reported that the levels of proline in transgenic rice increased over threefold compared with the levels of proline in WT rice after 4 °C cold treatment for 24 h [ 23 23 ]. 3.3. Effect of soil salinity on K + /Na + ratio and sugar accumulations of sweet sorghum 2 In the salt-affected soil, Na + is a small molecule that is easily absorbed into root tissues and transported throughout plant organs, leading to toxic ion damage, osmotic stress, and nutritional imbalance. In halophyte species, there are many salt-defense mechanisms, including ion homeostasis, osmoregulation, antioxidant, and hormonal regulation. An increase in stem or root K + /Na + ratio has been suggested as a possible ion homeostasis mechanism of the sweet sorghum salt stress tolerance [ 24 24 ]. Thus, the K + /Na + ratio can be utilized to identify salt-tolerant or salt-sensitive varieties [ 25 25 , 26 26 ]. In order to maintain the balance of K + /Na + in the cytoplasm under salt stress, the salt-tolerant sweet sorghum varieties could reach ion homeostasis via inhibiting Na + accumulation and accelerating K + accumulation in the cytoplasm. Generally, the K + /Na + ratio in the sweet sorghum stems and roots was affected by the sweet sorghum cultivar type and soil salinity. The results are shown in Fig. 3 Fig. 3 . The Na + increased with the increase in the soil salinity, while the K + was not significantly related to the soil salinity. The Na + in the sweet sorghum KF1210-3 root was highest, and the opposite result was obtained in the sweet sorghum KF1210-3 stem. Meanwhile, the K + /Na + ratio ( Fig. 4 Fig. 4 ) in the sweet sorghum stems decreased with the increase in the soil salinity. These results suggest that the sweet sorghum under the salt stress can inhibit the motion of Na + from root to stem in order to maintain ion homeostasis in cytoplasm. On the other hand, the Na + was positively related to total soluble sugars. The increase of soluble sugars in the sweet sorghum stems may play a key role in the osmotic adjustment to prevent water loss in the plant cells during salt stress [ 27 27 , 28 28 ]. The Brix degree content of KF1210-3 and KF1210-4 significantly increased with the increase of soil salinity. Silva et al. reported that in sorghum under salt stress, salt-tolerant cultivars could be enhanced in the soluble carbohydrate content. They suggested that the accumulation of soluble carbohydrates were significantly related to salt tolerance due to leaf osmotic adjustment under the salt stress. Juan et al. also reported that the sucrose content is an indicator of the salt tolerance in tomato [ 29 29 ]. 4. Conclusion 1 Heavy ion irradiation is an effective method to generate plant mutants and screen novel varieties to improve tolerance of the sweet sorghum in saline-alkali soil. The study was implemented in northwest China to assess the productivity of three sweet sorghum cultivars (KF1210-3, KF1210-4, and KFJT-CK) that were grown in intermediate (4.6 dSm −1 ) or in high (11.9 dSm −1 ) soil salinity to screen for highly tolerant sweet sorghum mutants. 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DOI: 10.1016/j.envexpbot.2004.07.004 http://doi.org/10.1016/j.envexpbot.2004.07.004 Evaluation of some nutritional and biochemical indicators in selecting salt-resistant tomato cultivars 10.1007/s41365-016-0086-6 This work was supported by the STS project (KFJ-EW-STS-086) and the Western Light Co-scholar (29Y406020) Program of the Chinese Academy of Sciences. 2015-11-23 2015-12-22 2016-01-06 2016-07-11 2016-08-20 2021-04-11 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2016 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-016-0086-6 http://dx.doi.org/10.1007/s41365-016-0086-6 . 2016 Nuclear Science and Techniques 04 27