Objective   Mechanism of red or blue light in regulating the root development of flue-cured tobacco seedlings was studied.

  Method   Effects of red or blue LED light exposure on the root growth and the synthesis and accumulation of endogenous gas signal molecule hydrogen sulfide (H₂S) in CB-1 tobacco seedlings were monitored.

  Results  After 7 days of the exposure to red or blue LED in comparison to white light, (1) the biomasses of aboveground parts and roots of the seedlings treated by red light increased by 74.62% and 15.64%, respectively, while the roots of the seedlings exposed to the blue LED decreased by 7.00%; (2) the H₂S content on the red light-treated plants increased by 61.72%, but reduced on the blue light-treated counterparts; (3) the red LED increased the activities of DES and CS by 24.28% and 25.61%, respectively, but the blue LED decreased them by 32.10% and 18.30%, respectively; (4) the NtDES expression in the red light-treated seedlings were 8.8-fold of that in the plants treated by white light, whereas the blue light resulted in merely 13.82% of what white light did.

  Conclusion   In contrast to blue LED, the exposure of the tobacco seedlings to red LED rose H₂S in the plants through increased expression of the key enzyme coding genes in the biosynthesis inducing a thriving generation of lateral roots.