Plants won't take a knock lying down

Sydney Morning Herald
February 22, 2001

By DeBOrah Smith

Scientists have worked out how plants can tell the difference between up and down.

Within seconds of being knocked over by wind or hail, they use a chemical that is also found in our brains to detect that something is wrong. Once they are sure their position has changed relative to gravity, the same chemical starts the process of bending the plant back upwards again.

The NASA-funded research could be helpful for extended space missions. American researcher Dr Wendy BOss told the annual conference of the American Association for the Advancement of Science that plants will have to be taken into space to provide astronauts with oxygen and food. "But before we create such long-term support systems, we need to know how gravity affects the growth of plants," she said.

The team found that 15 seconds after corn and oat plants were placed on their sides, levels of the chemical, inositol triphosphate, surged fivefold in a special part of their stems, known as the pulvinus. The chemical is found in large amounts in the human brain and helps cells communicate with each other.

After the initial surge, the plants waited for up to four hours, during which the level of the chemical fluctuated between the top and the BOttom of the pulvinus areas.

The researchers believe this delay allows the plants to rule out the possibility that they are just swaying in the breeze, rather than having been flattened. In particular, the plants work out whether little floating bits in their cells have been pulled to the BOttom of the cells by gravity.

Eventually the level of the chemical increases in the lower half of the pulvinus, causing the cells closest to the ground to grow longer in an irreversible process.