Effect of Citric Acid on the Rhizome Differentiation and Browing Inhibition of Cymbidium Nanulum Y.S.Wu et S.C.Chen

The rhizomes of Cymbidium nanulum Y.S.Wu et S.C.Chen were incubated on differentiation medium MS+NAA 0.5 mg/L+sucrose 30.0 g/L+TDZ 0.1 mg/L containing citric acid(CA)(0、0.1、0.2、0.5、1.0、2.0、5.0 g/L) for 50 days.With the increase of CA concentration ranging from 0 to 1.0 g/L,the activities of PPO,POD,PAL and the total phenol content were decreased gradually,the activities of SOD,CAT and the differentiation rate were increased gradually.Whereas,within 1.0 g/L to 5.0 g/L,the activities of PPO,POD,PAL and the total phenol content were increased gradually,the activities of SOD,CAT and the differentiation rate were decreased gradually.Compare to control,supplemented with appropriate concentration of CA on medium can reduce browning degree and promoted rhizome differentiation rate,the most appropriate concentration of CA was 1.0 g/L CA and the differentiation rate reached 4.48.