Effects of Selenium Ions on the Growth of Rice Seedlings

For investigating the effect of selenium on the growth of rice seedlings, this study used different concentrations of selenium ions (0, 0.5, 5, 10 and 20 µmol/L) to treat rice seedlings hydroponically. The experimental findings demonstrated that rice seedlings could grow and develop properly in the presence of a selenium deficiency (0 mol/L). Selenium ions had a positive impact on the development of rice seedlings at low and middle selenium concentrations of 0.5 mol/L and 5 mol/L, boosting plant height, above-ground fresh and dry weights. Selenium ions had a substantial inhibitory impact on the development of rice seedlings at high selenium concentrations of 10 mol/L and 20 mol/L.


Introduction
Rice (Oryza sativa L.), a grain product of the Gramineae family, is a major food commodity in China [1].Rice's starch grains are tiny and simple for humans to process and absorb; rice also includes a variety of nutrients such as protein, fat, vitamins, minerals, and so on; and the different nutrients are well organized with high rates of digestibility and absorption [2].
Selenium (Se) is one of microelements in nature [3].Selenium is mostly found in plants as biomacromolecules like selenoproteins, selenonucleic acids, selenopolysaccharides, and compounds like selenocysteine, selenocysteine, and selenomethionine [4].Selenium in soil is primarily categorized as selenate, selenite, selenide, elemental state selenium, organic state selenide, and volatile state selenium, with organic state selenide being the primary source of functional selenium in soil [5].Plants receive selenium through their roots and foliage, and the primary types absorbed are Se 4+ and Se 6+ [6].Selenium is necessary for human growth and development and is very important for the human body [7].Selenium engages in the body's regular immune function by being a component of active enzymes; thus, a lack of selenium in the human body leads to a decline in immunity and a rise in the prevalence of cardiovascular diseases, liver diseases, and other diseases [8].One of the major sources of selenium in the human body is obtaining trace components of selenium from everyday food [9].
Rice is one of the most essential grains in the world, providing people with nutrients and energy [10].Additionally, by adding exogenous selenium components, the accumulation of selenium in rice may be enhanced, and the selenium content in rice is an essential source of selenium for people's bodies [11].As a result, research into the influence of selenium on rice growth and development is strongly tied to human health.Nevertheless, the effect of selenium on rice growth is unknown.

Plant materials
The rice seeds used in this experiment were Zhong Hua 11 (kindly given by Prof. Zhou Hongkai, College of Coastal Agriculture, Guangdong Ocean University).

Rice seed germination treatment
Two hundred plump rice seeds were steeped in deionized water in a beaker for 24 hours in the dark.The rice seeds were sterilized with 75% ethanol for 1 minute and then immersed in 2% NaClO solution for 30 minutes.Following sterilization, the rice seeds were washed five times with sterile ionized water before being distributed uniformly on glass petri dishes lined with absorbent paper and germinated for one week at 25°C with a photoperiod of 12 h/h and a light intensity of 2000 lux.

Rice seedling hydroponic treatment
One week after germination of rice seeds, seedlings with similar height and main root length and good growth were selected and transplanted into plastic bottles containing various concentrations of selenium (0, 0.5, 5, 10, and 20 μmol/L Na 2 SeO 3 ) in Hoagland hydroponic nutrient solution [12], with 24 seedlings treated at each concentration.The rice seedlings were attached to the mouth of the plastic bottles with sponge plugs so that the rice seedlings' roots were totally submerged in the hydroponic nutrition solution, but the above-ground sections could not be immersed.Following transplantation, the rice seedlings were put in a constant temperature incubation environment at 25°C for culture.The hydroponic nutrient solution was then changed every 5 days.

Data statistics and analysis
Every 5 days, experimental data were collected, and 4 rice seedlings were chosen at random from each treatment group for each measurement.The growth of rice seedlings was analyzed by six data measurements in 25 days.The one-way ANOVA significance test was used to evaluate all data in this study, and the findings were reported as mean±standard deviation, with different lowercase letters indicating the significance of differences in experimental data.

Effects of selenium on plant height of rice seedlings
Different concentrations of 0, 0.5, 5, 10, and 20 mol/L selenium ions were used to treat rice seedlings in this experiment to investigate the influence of selenium on the height of rice seedlings, and the results of experimental data processing are provided in Table 1 and Figure 1(A-D).The experimental data on days 5, 15, and 25 demonstrated that the plant height of rice seedlings increased and then decreased with increasing selenium ion concentration, whereas the experimental data on days 10 and 20 revealed a continuous decreasing trend with increasing selenium ion concentration.The effect of selenium ion treatment was minimal throughout the hydroponic period, with the exception of 0.5 mol/L, which increased the plant height of rice seedlings (Figure 1B).Furthermore, the addition of 20 mol/L Se revealed the most substantial inhibitory impact (Figure 1E).In conclusion, high selenium concentrations inhibited plant height of rice seedlings, whereas low selenium concentrations promoted plant height.

Influences of selenium on stem base width of rice seedlings
For investigating the effect of selenium on stem base width of rice seedlings, five concentrations of 0, 0.5, 5, 10 and 20 µmol/L selenium were used to treat rice seedlings in this experiment.The results were shown in Table 2.In the first 15 days of hydroponics, there was no notable variation in stem base width of rice seedlings for all selenium treatment groups.The 0.5 mol/L selenium treatment group was significantly different from the other treatment groups on the 20th day of hydroponics treatment and showed a significant promotion effect; however, after the 25th day of culture, both 10 mol/L and 20 mol/L selenium treatment groups were markedly different from the control group, and the stem base width of rice seedlings decreased with increasing selenium concentration, indicating an inhibitory effect.Thus, high concentrations of selenium revealed the development of rice seedlings, whereas low concentrations of selenium promoted growth and development.

Effects of selenium on fresh weight of aboveground part of rice seedlings
For studying the influences of selenium on the fresh weight of above-ground parts of rice seedlings, different concentrations of (0, 0.5, 5, 10 and 20 µmol/L) selenium were used to treat rice seedlings in this experiment.The data were demonstrated in Table 3.In the first 15 days of hydroponics treatment, there was no substantial variation in the fresh weight of above-ground sections of rice seedlings, as shown in Table 3.After 25 days of incubation, significant differences were found between the high and low selenium concentration treatment groups, with the 0 mol/L selenium treatment group having the highest fresh weight (3018.3mg) of above-ground parts of rice seedlings and the 20 mol/L selenium treatment group having the lowest value, 993.6 mg.Thus, the results revealed that different concentrations of selenium treatment had no obvious effect on the fresh weight of above-ground parts of rice seedlings at the early stage, but there was a significant inhibitory effect of high concentration of selenium treatment after 25 days, and the inhibitory effect increased as selenium concentration increased.

Influences of selenium on above-ground dry weight of rice seedlings
For investigating the effect of selenium on above-ground dry weight of rice seedlings, five concentrations of 0, 0.5, 5, 10 and 20 µmol/L selenium were used to treat rice seedlings in this experiment.The results were presented in Table 4.As seen from Table 4, the dry weight data of above-ground parts of rice seedlings on day 10 and 15 of hydroponics were not significantly different among the treatment groups for each selenium ion concentration.On day 20, there were significant differences between all treatment groups and the control group except for 0.5 µmol/L selenium ion treatment group, which was not significantly different from the control group.The maximum dry weight of above-ground part of rice seedlings in the 0.5 µmol/L selenium ion concentration treatment group on day 25 was 460.7 mg, and there were significant differences between this treatment group and other treatment groups with higher selenium ion concentration, but no significant differences with the control group.The dry weight statistics of above-ground parts of rice seedlings on days 10 and 15 of hydroponics were not statistically different among the treatment groups, as shown in Table 4. On day 20, all treatment groups were statistically different from the control group, with the exception of the 0.5 mol/L selenium treatment group, which was not significantly different from the control group.On day 25, the maximum dry weight of above-ground rice seedlings in the 0.5 mol/L selenium treatment group was 460.7 mg.However, the dry weight of the above-ground portion of rice seedlings dropped numerically as the concentration of selenium increased.In conclusion, during hydroponic rice seedling cultivation, low concentrations of selenium promoted the accumulation of dry matter in the aboveground part of rice seedlings, whereas high concentrations of selenium inhibited the increase of dry weight in the aboveground part of rice seedlings.

Discussion
Selenium (Se), an essential trace element for both humans and animals, is crucial for the body's regular metabolic processes [13] (Yang et al., 2021).In particular, selenium has good auxiliary effects in antioxidant, fighting cancer, preventing cardiovascular diseases, and improving immunity [14,15].Inadequate intake of selenium can cause crucial system dysfunction and jeopardize health [16].However, because the human body cannot produce selenium, it must be obtained from outside sources.Currently, the most common method of supplementing selenium is to ingest selenium-containing pharmaceutical and dietary preparations, but these substances have a low utilization rate in the human body and have adverse effects.In comparison, plant transformation can turn more than 80% of exogenous inorganic selenium into organic selenium that is advantageous for human absorption.
Plants are the primary source of selenium in the human diet.In recent years, there has been a significant rise in study interest in the biological influence of selenium.Rice, being a significant food crop, may be an essential source of selenium for humans [17].As a result, current research on the impact of selenium on rice growth and development is extremely important.According to the findings of this study, selenium had a rather big influence on the development of rice seedlings.The high selenium treatment inhibited plant height, stem base width, above-ground fresh weight and dry weight of rice seedlings.While the 0.5 mol/L selenium treatment had a favorable impact on development of rice seedling.According to some research findings, adding the right amount of selenium can promote plant growth and development, resist environmental pollution and chemical stress, antagonize heavy metal absorption, enhance the plant's ability to resist disease, thus reducing the use of pesticides, while also promoting crop yield, changing the composition of the product, such as increasing selenium content, vitamin C content, protein content, and so on, and thus improving crop quality and flavor [18,19].However, special attention should be paid to the concentration of used selenium, because the range between the nutritional dose of selenium and the maximum safe intake is very narrow, and too high concentrations of selenium can have a toxic effect on the biological organism [20].

Conclusions
Under the conditions of selenium deficiency (0 mol/L), rice seedlings could grow and develop properly, and the rice plants displayed no visible aberrant signs.Under low selenium ion concentrations, such as 0.5 mol/L, selenium had a promotion impact on the growth and development of rice seedlings, increasing plant height, above-ground fresh weight and dry weight.However, under high selenium environments of 10 mol/L and 20 mol/L, selenium had a considerable inhibitory effect on rice seedling growth.

Figure 1
Figure 1 Growth of the aerial parts of rice seedlings under different selenium ion concentration treatments on the 25th day.A: 0 µmol/L; B: 0.5 µmol/L; C: 5 µmol/L; D: 10 µmol/L; E: 20 µmol/L.(bars=10 cm) This research was funded by the Project of Marine Young Talent Innovation of Zhanjiang City (210818004542097), the College Students Innovation and Entrepreneurship Training Program (S202210566025), the Project of Rural Science and Technology Team "One-to-One" Service to Help the Town Full Coverage of Action Funding in Zhanjiang City (2022NCKJ01), the College Students Innovation Entrepreneurship Training Program (S202210566022), the Project of Social Services of Rural Science and Technology Specialists of Guangdong Ocean University (080503052212), and Maintenance Expenses of Key Construction Disciplines in High-level University of Crop Science (080508052201).

Table 1
Effects of different concentrations of Se on the height of rice seedlings

Table 2
Effects of different concentrations of selenium on the base width of rice seedlings

Table 3
Results of different concentrations of selenium on the fresh weight of the above-ground parts of rice seedlings.

Table 4
Effects of different concentrations of selenium on the dry weight of the aerial parts of rice seedlings