Gravitropism is the movement of a plant based on the strength and direction of gravity. For example, when a seed sprouts, the roots always grow down into the soil, whereas the stem grows upward. A germinating seed can be turned upside down several times and the root will still start to bend downwards. A team of biologists from the University of California, Riverside has used chemical genomics to identify novel compounds that affect this ability of plants to alter their direction of growth in response to gravity.

Tonoplast aggregrates (Courtesy: University of California, Riverside)The team published its findings in the Proceedings of the National Academy of Sciences. The researchers analysed some 10,000 small molecules to identify those that could positively or negatively affect gravity’s effect on plant growth, which is closely linked to the movement of proteins through plant cell membranes.
The work focusses on using these molecules to disrupt, or reorient the growth of the plant in any particular direction. This is easier to do than other approaches, which use genetic mutations to alter the plant behavior. The team narrowed their search down to 4 chemicals, which affected gravitropism and the movement of proteins through membranes within the plant cell. The chemicals affect the growth of tonoplasts (membrane surrounding the vacuole), and this indirectly regulates the direction in which a plant will grow.
This research was supported by NASA, and will have applications such as growing plants in space. If successful, this would allow astronauts to grow their own food, and also regenerate the oxygen during long space missions.