Examples of Bioindicators
One significant aspect of the innovation will be identification of indicator species appropriate to the local cultivation system, sensitive to the condition of interest, and able to provide an observable signal. In 1998, Kovalchuk et al., Bioindicator plants to detect nuclear pollution, engineered Arabidopsis plants to analyze the influence of chronic irradiation from the environment of the Chernobyl exclusion zone, on the stability of plant genomes. In this example, bioindicator plants were shown to be an effective indicator of change within the surrounding environment.
Another example encompasses research conducted by Aresa, a private company originally based at the University of Copenhagen, that is marketing bioindicator plants commercially. Aresa genetically engineered a weedy plant with a gene that produced a red-colored product when the gene’s expression was induced by a receptor as a breakdown product of TNT. This enabled the plant to be used as a sentinel for the presence of soil residues indicating the presence of land mines.
The underlying mechanism by which the color change occurs is via an altered regulation of the natural pigment biosynthetic pathways in the plants. Familiarly, many plants turn reddish in autumn or as a result of stressed growth conditions when synthesis of the red (anthocyanin) pigments dominates over the normal green color. The genetically engineered plants are modified in a way that allows these plants to turn red-purple if triggered by TNT in the soil.
Shown below2 at left is a photo of a soil tray planted with the engineered bioindicator seed in which the upper right quadrant of the soil has been drenched with liquid TNT. The photo at the right indicates the size of isolated plants.
Gene products that might be applied to measuring iron and phosphate levels and heavy metals in soil have been identified by scientists3, and Aresa has announced a plan to commercialize the latter for bioremediation4. Unfortunately, in the iron and phosphate plant sentinel prototype systems, the effects of the measurement are seen in the roots5 (not readily visible to the farmer) or as a very slow change in the shoots6 (timing that may not facilitate effective response measures).
Ideally, changes in an indicator species would be phenotypes that could be rapidly and easily detected by farmers, but that may not persist very long. Possible examples include a color change on a de-greened background (Medford et al.), a shape change or a texture change, such as the presence or absence of trichomes. Such changes might appear in leaves or stem segments produced only in plastochrons immediately associated with the stress, and leaf or stem segment production would revert to normal in sectors produced after the stress passes.
Some of our ideas about these changes are on the BioForge. If you have ideas about such changes and how to effect them, please make a posting in the forum.
To see more about patents and patent applications that cover the field of bioindicators or biosentinels, click here.
2 Images are used with permission, from Aresa’s website, www.aresa.dk
3 Vert G, Grotz N, Dedaldechampa F, Gaymard F, Guerinot ML, Briat J-F, and Curie C (2002) ‘IRT1, an Arabidopsis transporter essential for iron uptake from the soil and for plant growth’. Plant Cell 14: 1223-1233
5 Vert et al. ibid.
6 Hammond JP, Bennett MJ, Bowen HC, Martin R. Broadley MR, Eastwood DC, May ST, Rahn C, Swarup R, Woolaway KE, and White PJ (2003) ‘Changes in gene expression in Arabidopsis shoots during phosphate starvation and the potential for developing smart plants’. Plant Physiology 132: 578-596.