text: In Runyon et al. 2006, the researchers demonstrate how the parasitic plant, Cuscuta pentagona (field dodder), uses VOCs to interact with various hosts and determine locations. Dodder seedlings show direct growth toward tomato plants (Lycopersicon esculentum) and, specifically, tomato plant volatile organic compounds. This was tested by growing a dodder weed seedling in a contained environment, connected to two different chambers. One chamber contained tomato VOCs while the other had artificial tomato plants. After 4 days of growth, the dodder weed seedling showed a significant growth towards the direction of the chamber with tomato VOCs. Their experiments also showed that the dodder weed seedlings could distinguish between wheat (Triticum aestivum) VOCs and tomato plant volatiles. As when one chamber was filled with each of the two different VOCs, dodder weeds grew towards tomato plants as one of the wheat VOCs is repellent. These findings show evidence that volatile organic compounds determine ecological interactions between plant species and show statistical significance that the dodder weed can distinguish between different plant species by sensing their VOCs.
  Tomato plant to plant communication is further examined in Zebelo et al. 2012, which studies tomato plant response to herbivory. Upon herbivory by Spodoptera littoralis, tomato plants emit VOCs that are released into the atmosphere and induce responses in neighboring tomato plants. When the herbivory-induced VOCs bind to receptors on other nearby tomato plants, responses occur within seconds. The neighboring plants experience a rapid depolarization in cell potential and increase in cytosolic calcium. Plant receptors are most commonly found on plasma membranes as well as within the cytosol, endoplasmic reticulum, nucleus, and other cellular compartments. VOCs that bind to plant receptors often induce signal amplification by action of secondary messengers including calcium influx as seen in response to neighboring herbivory. These emitted volatiles were measured by GC-MS and the most notable were 2-hexenal and 3-hexenal acetate. It was found that depolarization increased with increasing green leaf volatile concentrations. These results indicate that tomato plants communicate with one another via airborne volatile cues, and when these VOC's are perceived by receptor plants, responses such as depolarization and calcium influx occur within seconds.