Effect of Different Light Quality on Photosynthetic Characteristics of Cucumber Leaves

Cucumber (Cucumis sativus L. cultivar “Changchun Mici”) seedlings were cultured in Hoagland solution under irradiation with different light spectra (8 h per day) for 20 days. The red light (λ max 658 nm, λ 1/2 25 nm), blue light (λ max 450 nm, λ 1/2 43 nm) and white fluorescent light possessed the same fluent rate (20 μmol·m -2 ·s -1 ). The experimental results showed that chlorophyll content of the leaves grown under white light was 7% and 22.4% higher than those in red and blue light, respectively. Compared with white and blue light, red light induced a lower Chl a/b ratio and a higher level of Chl b in the cucumber leaves. Measurements of the low temperature (77 K) fluorescence emission spectra and kinetics of Chl a fluorescence induction of the leaves proved that the leaves grown under red light expressed the highest PSⅡ and the lowest PSⅠ activities while the leaves under blue light had the lowest PSⅡ and the highest PSⅠ activities. The O 2 evolution rate of red light_grown leaves was 44.9% higher than that of the white light_grown leaves, while blue light effect was similar to that of white in respect of O 2 evolution. It is concluded that light quality is an important factor in regulating the development and activities of PSⅡ and PSⅠ and the O 2 evolution of photosynthesis in cucumber leaves.