Abstract:When cucumber seedlings (Cucumis sativus L. cv. Aonagajibai) were treated with aqueous solution of BA (10–5mol/1 and 10–8mol/l) by spraying application, the amount of NPR protein was increased and the NPR activity was promoted. The contents of protochlorophyl, lide (Pchlide) and NADPH as the substrates of the enzyme reaction, were also increased remarkably. 2. The amount of Pchlide and NPR protein decreased rapidly when treated with red light. BA plays the role in the protection against the damage of enzyme activity by light and then decreasing the destruction of NPR protein. BA increased the content of Pchlide and NADPH, so the NPR activity was maintained at a higher level although in light condition. 3. Because that BA increased the content of NPR protein and the reaction substrate such as NADPH and Pchlide, the NPR activity was promoted. So, the rate of chlorophyll biosynthesis was rapid, and the content of chlorophyll increased. The leaf turns to dark green.