Shoot length and phenolic content of plants grown in light of different colors

Seedlings of six varieties of plants were grown for 8-13 days in blue, red, far-red, white light, or in darkness. Shoots were then measured in length, extracted and phenolics determined. The total phenolic content was measured spectrophotometrically after addition of Folin-Ciocalteu's reagent. In all cases, the dark grown seedlings were longer than those of corresponding plants grown in white light and they had lower endogenous levels of phenolics. Seedlings grown in blue light exhibited the shortest shoot length and had the highest phenolic concentration. If phenolics are causally related to the reduced size, then addition of these extracts should inhibit growth induced by GA3. Extracts from radish seedlings (100gFW/ml) grown under red light and darkness inhibited GA-induced growth in pea seedlings. Extracts (1000gFW/ml) from pea seedlings grown under blue light and darkness inhibited both endogenous and GA-induced shoot growth. The inhibition was greater with the extract from seedlings grown in blue light. These data suggest that phenolics may be involved and play a regulatory role in the light-mediated inhibition of growth. Both the phytochrome and blue light-absorbing pigments appear to be involved in the processes leading to synthesis of phenolic compounds in light-grown plants.