Abstract: This study explored the effects of supplemental light quality and illumination duration on photosynthetic pigment contents and antioxidant enzyme activities of greenhouse cucumber seedling leaves. Three lighting durations (2, 4, and 8 h) of supplemental lighting applied were combined with five light qualities: (i) 100% White light (W), (ii) 100% Red light (R), (iii) 100% Blue light (B), (iv) a 3:7 mixture of B and R, (v) a 2:8 mixture of B and R. The effects of white, red, blue, red and blue mixed light on photosynthetic pigment contents, MDA contents, soluble proteins contents and antioxidant enzyme activities of greenhouse cucumber seedling leaves were studied. The results showed that, compared with natural light, supplemental lighting could significantly improve the chlorophyll a, chlorophyll b, chlorophyll content and carotenoid content of cucumber seedling, and the effect of combined light components (7R/3B and 8R/2B) for the duration of 4 h were the most significant. And that supplemental lighting could significantly improve the content of soluble protein,blue light had the greatest the content of soluble protein. Meanwhile, supplemental blue lighting for 4 h promoted significantly the contents of soluble protein and the activities of anti-oxidant enzymes (POD, SOD, APX and CAT). In contrast, supplemental blue lighting for 4 h decreased the contents of MDA. These results indicate that supplemental blue lighting for 4 h prevent the senescence by maintaining high levels of anti-oxidant enzymes.

Key words: light emitting diode (LED), light quality, photosynthetic pigment, soluble protein content, antioxidant enzyme