Structural and physiological changes of Chromolaena odorata during formation of adventitious root.
Objective: The anatomic structure and physiological changes of Chromolaena odorata were investigated to understand rooting characteristics during formation of adventitious root, in order to lay the foundation for further clarifying its strong asexual reproduction mechanism. Method: The formation of C. orodata adventitious root in different base and water contents of base materials was investigated respectively in the cutting experiment. Meanwhile, the changes of anatomic structure were observed, and the endogenous hormones content, POD activity and flavonoids content were determined. Result: The results showed that the rooting rates reached up to 100.0% in 3 base materials viz., vegetable garden soil, red soil and river sand, respectively. The cuttings were easy to form adventitious root in base materials with water content of 20%-60%, while which couldn't form adventitious root in base materials with water content at 0 or above 80%. The observed result of anatomical structure showed that C. orodata stem had thin cortex and large pith, without ring-like sclerenchyma cells in cortex, the adventitious root primordium of cuttings was generated from fascicular cambium, and there was not callus formation in rooting process, moreover, the formations of root primordium and adventitious root were found on 3 and 7 d after cutting, respectively. In addition, during adventitious root formation, the physiological indexes changed significantly; the content of IAA first increased, then decreased and increased again; ABA and flavonoids as rooting inhibitors, their content presented declining trend on the whole; ZT content was peaked on 3 d after cutting. Furthermore, the minimum POD activity was found on 1 d after cutting, the maximum was found on 3 d after cutting, and the POD activity in rooting process after cutting was significantly higher than that before cutting. Conclusion: C. orodata has high environmental adaptability during adventitious root formation, and its anatomic structure and change of endogenous hormones content in the process of cuttage are in accordance with feature of being easy to form adventitious roots.