Effect of light intensity on the hypocotyl length of Arabidopsis thaliana during germination


  • Angie H. Chan
  • Rahul Chawla
  • Angela S. Johnston
  • Keun Young Lee
  • Mandip S. Parmar


In this experiment, seeds of the Arabidopsis thaliana, a model plant species, were subjected to different light intensities and the length of the hypocotyl was examined during germination. We hypothesized that A. thaliana seeds cultured under high light intensity would have longer hypocotyls than those cultured under low light intensity and no light. The seeds were grown in an incubator at 17 degrees Celsius at light intensities: 0 lux, 1396 lux, 7000 lux (optimal) and 12520 lux and the hypocotyl lengths were measured approximately every 24 hours for one week. Results did not support our hypothesis, and we found that A. thaliana cultured in the absence of light had the longest hypocotyls. More specifically, A. thaliana grew to a length of: 6.08 +2.00mm under no light, 1.50 +0.28mm at a light intensity of 1395 lux, 2.38 +0.42mm at 7000 lux, and 1.31 +0.25mm at 12520 lux, in a time frame of one week, or 168 hours. We concluded that in the absence of light, A. thaliana develops by skotomorphogenesis rather than photomorphogenesis, causing the length of the hypocotyl to elongate faster than under light conditions. In the light treatments, the hypocotyl length after one week was longest at the optimum light intensity and significantly shorter at both lower and higher light intensities.