Effects of Ethylene Associated Compounds On In Vitro Growth and Differentiation of Cymbidium Sinense Rhizomes In Media for Rhizome Propagation and Shoot Differentiation

The gaseous plant hormone, ethylene, can induce a great range of plant responses in growth and development. In tissue culture, ethylene may promote or inhibit shoot formation, depending on species. Rhizome culture of Cymbidium sinense in cytokinin-free medium resulted in rhizome proliferation but shoot differentiation in cytokinin-added medium. In this study, we investigated the effects of 1-aminocyclopropane-1-carboxylic acid (ACC), aminooxyacetic acid (AOA), and AgNO₃ on shoot formation in rhizome culture. Rhizome sections of Cym. sinense 'Rui Bao' x Cym. sinense 'Guang Hua Die' was used as plant material; each chemical was tested at concentrations of 0, 50, and 100 μM. Ethylene evolution was monitored by gas chromatography. Supplementing ACC in rhizome propagation medium promoted rhizome growth and branching; adding AgNO₃ suppressed rhizome growth but increased shoot differentiation and growth. In shoot differentiation medium, adding ACC significantly inhibited shoot and root growth, while AgNO₃ increased shoot growth. These results implied that ethylene may promote rhizome growth but inhibit shoot formation in Cymbidium sinense, thought it should be further confirmed. The addition of ACC or AgNO₃ increased ethylene evolution. It seemed that AgNO₃ increased ethylene synthesis but inhibited ethylene action. Adding 50 or 100 μM AOA in both media resulted in suppressing rhizome and shoot growth; it may be attributed to that these concentrations were too high and caused toxicity.