Plants are extremely sensitive to their environment, able to detect and respond to such stimuli as gravity, touch, light, moisture, and nutrient gradients. One of the most common outcomes upon sensing a stimulus is for the plant to undergo differential growth either toward or away from the stimulus. Growth responses toward or away from stimuli are known as tropisms. Plant tropisms have been the object of scientific study for over 200 years, with each successive generation of researcher applying current state-of-the-art technologies and approaches to further our understanding of the mechanisms responsible for growth regulation. Research on tropisms provides a point of integration today among the fields of cell biology, genetics, molecular biology, biophysics, biochemistry, and physiology.
The images in this project make use of a reporter gene known as GFP, which stands for green fluorescent protein, a naturally occurring protein found originally in the jellyfish, Aequoria victoria. The cloning of the gene encoding this fluorescent protein made it possible to label virtually any gene product in vivo, without the addition of toxic dyes, opening up a whole world of possible experiments in cell and molecular biology.
In the case of the images in the experiment published here, the GFP gene was fused to a promoter element that is activated in response to the plant hormone auxin (also known by its chemical name, indole-3 acetic acid). The specific details of this reporter gene were described in the article, "Gravity-regulated differential auxin transport from columella to lateral root cap cells."
All images copyright of Chris Wolverton.