Responses to intermittent exposure to green light during the dark period in Arabidopsis thaliana and possible involvement of cryptochrome 2

The effects of green light treatment during the dark period were examined in Arabidopsis thaliana as a first step to understanding the mechanism of artificial green light effects in plants. Plants were grown under long-day conditions (an 18-h light and a 6-h dark cycle) and were intermittently exposed to green light during the dark period for 2 h 3 times a week. This green light treatment suppressed the elongation of roots and hypocotyls in wild-type plants. However, the green lightinduced changes were not significant in the cry2 mutant that is deficient in the blue light receptor cryptochrome 2. The green light treatment elevated both jasmonic acid and salicylic acid levels in the wild-type plants but the elevation of the jasmonic acid level was impaired in the cry2 mutant plants. These results suggest that intermittent exposure to green light triggers artificial responses in Arabidopsis plants that do not occur in the natural environment, and that cryptochrome 2-dependent and jasmonic acid-mediated responses may be partly involved in the effect of green light on plants.