Abstract: The content of DNA, RNA and total nucleic acid ( TNA) in stem apex increased
gradually before the inflorescence differentiation, and reached a peak at the inflorescence differentiation, then decreased to a proper level at one week after the inflorescence differentiation and increased again to form little peak at the former stage of curd formation, then decreased again at the late stage of curd formation. The RNA/ DNA rat io went down rapidly just before the emergence of curd, and went up gradually from the emergence to harvest of curd. The content of Calmodulin ( CaM) in stem apex went up gradually before the inflorescence differentiation and reached a peak after one week of the in florescence differentiation, then went down during curd format ion. N-Zn nutrition could promote the metabolism of nucleic acid and CaM, but different N-Zn nutrition had different effects on the synthetic activity of nucleic acid. Suitable N and Zn nutrit ion had a marked promoting effect on the synthesis of CaM.

Key words: Broccoli ( Brassica olerecea L. var. italica Planch), Nucleic acid, Calmodulin( CaM), Inflorescence differentiation, N-Zn nutrition