Effect of sodium hypochlorite on physiological characteristics of Nitraria tangutorum open tissue culture seedlings

Taking the Nitraria tangutorum tissue culture seedlings grown by traditional tissue culture technology as a control, using an open tissue culture method, different concentrations of the bacteriostatic agent sodium hypochlorite were added to N. tangutorum spur medium. According to physiological characteristics, the effects of the bacteriostatic agent were evaluated for tissue cultured N. tangutorum plants. The results showed that with the increase in the sodium hypochlorite concentration, the antibacterial effect on N. tangutorum medium gradually increased. Sodium hypochlorite at a concentration up to 50 mg·L⁻¹ inhibited the root number and root length of N. tangutorum tissue culture seedlings. A sodium hypochlorite concentration of 15 ~ 20 mg·L⁻¹ promotes the growth of N. tangutorum tissue culture seedlings. The addition of sodium hypochlorite in the open tissue culture enhances the autogenous metabolism of the tissue culture seedlings and significantly increases the concentration of superoxide anions (O₂·^–) and hydrogen peroxide (H₂O₂). Compared with the traditional tissue culture, the accumulation of nutrients was inhibited in the tissue-cultured seedlings of N. tangutorum. Free proline (Pro), soluble sugar (SS), and soluble protein (SP) accumulate at high concentrations; when the sodium hypochlorite concentration is greater than 20 mg·L⁻¹, the activities of antioxidant enzymes catalase (CAT), superoxide (SOD), peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL) are significantly different compared with the control (P < 0.05). The comprehensive consideration of morphological indicators indicated that a sodium hypochlorite concentration of 50 mg·L⁻¹ is extremely unfavorable for the growth of N. tangutorum tissue culture seedlings. Sodium hypochlorite at a concentration of 15 ~ 20 mg·L⁻¹ can be used as a bacteriostatic agent for Nitraria open tissue culture.