Abstract:

Objective: To study the characteristics of rooting anatomical structure, and to investigate and analyze the dynamic changes and effects of endogenous hormones, oxidases and nutrients in the process of adventitious root development during softwood cuttings of Eucommia ulmoides, so as to provide reference for further research on the development mechanism and regulation techniques of E. ulmoides. Method: The E. ulmoides 'Huazhong No.6' semi-lignified twigs were used as the experimental material, the development process of adventitious roots was investigated by observing the anatomical structure of its paraffin sections that were made of the basis of cuttings collected regularly; the content of IAA, GA₃, ABA and ZR of E. ulmoides was determined by using HPLC-MS/MS; the activity of IAAO, POD, PPO was determined by colorimetric method; soluble sugar, soluble protein and total nitrogen were determined by the anthrone-sulfate method, Coomassie brilliant blue method and Kjeldahl method. Result: 1) The adventitious roots primordium of E. ulmoides was differentiated from the vascular cambium parenchyma cell of bark, which belongs to the induce-to-root type of the bark. The ontogeny process of adventitious roots can be divided into four stages: induction period (0-12 d after cutting), initiation period (12-22 d after cutting), expression period (22-32 d after cutting) and elongation period (32-53 d after cutting). It can be observed that there are young white adventitious roots breaking through the cortex at the base of the cuttings during the expression period. 2) The average number of adventitious roots in the treatment group with special rooting agent of E. ulmoides can reach 25.6, which was 20 more than of the control group treated with water. The average root length was 8.41 cm, which was about 2 times of the control group; The rooting rate was 85.3%, an increase of 60%. 3)IAA had significant function in the rooting process of E. ulmoides. The activity of POD and PPO increased first, then decreased, the activity of IAAO decreased first and increased later. Nutrients accumulated before rooting, and their content decreased after rooting. Conclusion: The adventitious root formation of E. ulmoides belongs to the type induce-to-root in the bark. The dynamic changes of various physiological indicators are consistent with the development of adventitious roots. IAA is a key hormone for inducing adventitious roots. During the critical period of adventitious root formation, the increase in IAA content is the key to inducing root primordium. Meanwhile, IAAO activity decreases, POD and PPO activity increases, and the nutrients rapidly accumulate, which are closely related to rooting.

Key words: Eucommia ulmoides, softwood cutting, anatomical structure, endogenous hormones, oxidases, nutrients