Abstract
Phototropins (phot1 and phot2) are blue light receptors for phototropism, chloroplast movement, leaf expansion, and stomatal opening. All these responses are thought to optimize photosynthesis, by helping to capture light energy efficiently, reduce photodamage, and acquire CO2. However, experimental evidence for the promotion of plant growth through phototropins is lacking. Here we report that growth in Arabidopsis dramatically increases in response to very low intensity of blue light superimposed on red light, and that phototropin-deficient mutants lack this response. The effect was prominent under low photosynthetically active radiation of background red light. We also showed that the blue light induced growth enhancement was correlated with the occurrence of phototropins-mediated responses including chloroplasts accumulation, stomatal opening, and leaf expansion. These results suggest that phototropins promote plant growth by controlling and integrating various responses that optimize photosynthesis under low photosynthetically active radiation in the natural environment.
