Effects of day length, light quality and ethylene on PHYTOCHROME B expression during stem elongation in Stellaria longipes

Abstract

The prairie ecotype of Stellaria longipes (Caryophyllaceae) is highly responsive to light and is a shade avoider. Using the prairie ecotype as a model, we investigated the expression of the PHYTOCHROME B (PHYB) gene in response to different ratios of red to far-red light (R/FR), photoperiods and ethephon, an ethylene producing compound. This was done to examine the potential role of the PHYB and its interaction with ethylene in determining the plasticity of stem elongation. The PHYB gene was constitutively expressed in flowers, leaves, stems, and roots. The relative transcript abundance of the PHYB gene increased significantly upon transfer of etiolated-seedlings to light. The level of the PHYB gene transcript under elevated R/FR (3.5) was significantly higher than that under lower R/FR (0.7) in de-etiolated-mature plants. Long day photoperiod (16 h light/day, LD) significantly promoted stem growth, whereas plants under short day photoperiod (8 h light/day, SD) showed minor elongation. Interestingly, under LD, but not under SD, the level of PHYB mRNA significantly correlated with stem elongation. The plants treated with high concentration of ethephon (10.0 mol m−3) showed a 55% decrease in PHYB transcript within the first 4 days after treatment, and the level of PHYB transcript was significantly lower than that in control plants and the plants treated with a lower concentration of ethephon (0.1 mol m−3). Taken together with our earlier studies related to stem elongation, our results suggest that the level of PHYB gene transcription on day 4 is critical for the initiation of stem elongation. After this stage, a relatively high level of the PHYB gene transcription might be important for maintaining stem elongation of the prairie plants of S. longipes.