Abstract:Excised cotyledons of mature cucumber seeds were cultured on wet filter paper without exogenous hormones and nutrients (26 ±1℃, 2.92 W m-2, 14h day length). During 0 to 4 days after excision, the size and fresh weight of cotyledons increased rapidly, and the dry weight remained almost constant. After the 4th day of culture, the fresh weight and the area of cotyledons continued to increase, although more slowly than before, while the dry weight decreased quickly (Fig. 1). Respiration intensity and chlorophyll content of the cotyledons increased quickly before the 4th day, and reached the peak simultaneously at day 4, and then declined obviously (Fig. 2). The contents of mineral elements in detached cotyledons appeared to change within 0 to the 6th day (Table 1). With the exception of putrescine content decreasing slightly in the 2nd day of culture, all of the contents of spermine. spermidine and cadaverine in cotyiedons increased steadily. butthe increment was different. Thus, polyamine synthesis in cucumber cotyledons was not generally impaired after excision (Table 2). The contents of GA3 and ABA in cotyledons were to some extent increased, and the contents of IAA and ZT increased markedly, indicating that the detached cotyledons were capable of synthesizing the hormones during this period (Table 2). The contents of DNA, RNA and acid-soluble protein increased obviously within the first 2 days, while DNA content declined quickly, and the acid-soluble protein content fluctuated, meanwhile, RNA content remained almost unchanged. In the first 4 day, the content of alkali-soluble protein decreased continuously (Fig. 3), indicating that the detached cotyledons kept metabolic activity of nucleic acids and proteins.
