Effects of Different Combinations of Red and Blue Light on Morphology and Photosynthetic Characteristic of Tomato Seedlings

Blue and red light are spectral wavelengths more effective for plants. The effects of different ratios of red and blue light （R/B=2, R/B=4, R/B=8, R/B=12） provided by LEDs on morphology and photosynthetic characteristics of tomato seedlings were studied. The results showed that plant height, stem diameter, fresh weight, dry weight, seedling index and G value increased with the increase of R/B ratio until 8. On the contrary, SPDA value decreased with the increase of R/B ratio. Photosynthetic characteristics were measured by CO 2 assimilation （ Pn ）, stomatal conductance （ gs ） and intracellular CO 2 concentration （ Ci） . Pn and gs decreased with the increase of R/B ratio. Furthermore, similar trend was investigated in photochemical quenching （qP） and electron transport rate （ETR）. Results of this study suggest that compared with white LED, appropriate combination of red and blue light can enhance plant growth and photosynthetic characteristics, and the optimal blue/red ratio for tomato growth was R/B=8.

Red and Blue Lights Significantly Affect Photosynthetic Properties and Ultrastructure of Mesophyll Cells in Senescing Grape Leaves

Light quality significantly affects photosynthetic efficiency in plants. The mechanisms for how light quality affects photosynthesis in grape is poorly understood. Therefore, to investigate the effects of different light qualities on chloroplast ultrastructure and photosynthesis efficiency, two grape cultivars ‘Italia'(slower speed of leaf senescence) and ‘Centennial Seedless'(faster speed of leaf senescence) grown under protected and delayed conditions were used. The three treatments, replicated three times, were control(no supplemental lighting), red light and blue light. Chlorophyll content, net photosynthetic rate, and the ratio of F_v/F_m significantly increased in red light relative to the control. The opposite trend was observed in blue light in the early phase of leaf senescence. At later stages, physiological indexes were gradually higher than that of control, resulting in a delay in leaf senescence. Compared to the control, red and blue light both significantly increased the chlorophyll a/b ratio. Electron microscopy showed that blue light caused severe damage to the fine structure of chloroplasts at early stages of leaf senescence, but effects at later stages of leaf senescence became less severe compared to the control. The degradation of chloroplast ultrastructure was apparently delayed in red light throughout the experimental timeframe compared to other treatments. In this experiment, ‘Italia' showed higher chlorophyll content, net photosynthetic rate, ratios of F_v/F_m, chlorophyll a/b and better preserved chloroplast ultrastructure relative to ‘Centennial Seedless', resulting in a slower rate of leaf senescence.