Effects of Blue and Red Lights on Gibberellin Metabolism in Tomato Seedlings

Light quality is an important environmental factor that regulates stem length of the tomato (Solanum lycopersicum). Previously, we showed that the stem length of tomato seedlings grown under red (R) light emitting diodes (LEDs) was significantly longer than that of seedlings grown under blue (B) LEDs or a mixture of B and R LEDs; further, the light intensity of B LED negatively correlated with the stem length. This study aimed to elucidate the mechanism of how B and R lights affect stem elongation. We analyzed the levels of gibberellins (GAs) and the expression of genes associated with their metabolism in tomato seedlings grown under different B and R light conditions. The level of bioactive GA, GA4, was significantly higher in the seedlings grown under R LED than in those grown under other light conditions. In addition, an increase in the B to R light ratio increased the transcript level of the GA inactivation enzyme gene, SlGA2ox7. Moreover, the transcript level of SlGA2ox7 increased with the intensity of B light, and was negatively correlated with the stem length of the seedlings. These results indicated that the B light intensity controlled GA inactivation of the seedlings, and endogenous GA contents may affect stem elongation. Further, we found that the transcript level of the GA biosynthesis enzyme gene, SlGA3ox3, in the seedlings grown under R LED was significantly higher than that under other light conditions. This could be due to depletion of B light and suggests that GA biosynthesis may be involved in the stem elongation of seedlings grown under low B light conditions.