LAUSR

Abstract Red and blue light play pivotal roles on mediating plant developmental processes, while evidence is accumulating that responses to changes in light spectrum are species dependent. This study aims to evaluate responses in cucumber and tomato which are major horticultural species and model plants for light spectrum studies, to red and blue light at different integrational levels, and at distinguishing to what extent these two species differ from each other. Plants were grown under a range of blue (B) light percentage: 0B, 25B, 50B, 75B, and 100B, the remaining percentage was red (R) light, with identical photosynthetic photon flux density (100 μmol⋅m−2⋅s-1). Peak intensities of B and R were at wavelengths of 454 nm and 663 nm, respectively. We showed that an increase in the blue light percentage resulted in a decreased plant height in both species, except under 100B where cucumber exhibited the greatest plant height, while in tomato the tallest plants were under 0B. Cucumber grown under 100B had the greatest shoot dry weight and largest leaf area, whereas in tomato 25B had the greatest plant growth. In both species, the function of leaf photosynthetic apparatus was strongly repressed by 0B, compared with the other treatments, while the magnitude of this repression was greater in cucumber than in tomato. Leaf total nitrogen, total carbon and chlorophyll contents were lowest under 0B in both species. HY5 expression exhibited limited response to 0B, but it was significantly increased by blue light (i.e. 50B and 100B) except with cucumber that was non-sensitive to 100B. We conclude that blue light is needed for maintaining normal plant growth and developmental processes, and cucumber is more sensitive to red and blue light than tomato, indicating that plant responses to red and blue light are species specific. Our research stresses the significance to consider the species or even cultivar difference when drawing conclusions from light quality study.