What happens to plant growth when you remove gravity?

December 7, 2012
This shows Jeff Williams in the ISS: root ‘waving’ and ‘skewing’ occur in spaceflight plants independently of gravity. (BMC Plant Biology). Credit: NASA

It is well known that plant growth patterns are influenced by a variety of stimuli, gravity being one amongst many. On Earth plant roots exhibit characteristic behaviours called 'waving' and 'skewing', which were thought to be gravity-dependent events. However, Arabidopsis plants grown on the International Space Station (ISS) have proved this theory wrong, according to a study published in BioMed Central's open access journal BMC Plant Biology: root 'waving' and 'skewing' occur in spaceflight plants independently of gravity.

In , 'waving' consists of a series of regular, undulating changes in the direction of root tips during growth. It is thought to be associated with perception and avoidance of obstacles, and is dependent on gravity sensing and responsiveness. 'Skewing' is the slanted progression of roots growing along a near-vertical surface. It is thought to be a deviation of the roots from the direction of gravity and also subject to similar mechanisms that affect waving. Even though the precise basis of these growth patterns is not well understood, gravity is considered to be a major player in these processes.

To test what happens to plant root growth when you remove gravity entirely, a research team from the University of Florida, Gainesville, USA, grew two types of Arabidopsis thaliana cultivars - Wassilewskija (WS) and Columbia (Col-0) – on the ISS. The plants were grown in specialized growth units that combined a plant habitat with a camera system which captured images every six hours. Imaging hardware delivered the telemetric data in real-time from the ISS, and comparable ground controls were grown at the Kennedy Space Centre.

The phenomenon of negative-phototropism in plant roots is well documented, but its role in orienting root growth is still being explored. The authors found that, in the absence of gravity, but in the presence of directional light, spaceflight roots remained strongly negatively phototropic and grew in the opposite direction of the shoot growth, as they do back on Earth. The path taken by the roots as they grew also retained the complex patterns of waving and skewing, characteristic of Earth-grown, gravity-influenced, roots. Furthermore, while in orbit, each cultivar retained its unique terrestrial skewing pattern.

However, the team observed that the degree of waving exhibited by the plants in space did not match what would be predicted for roots showing an equivalent amount of skewing back on Earth. In space, waving was far more subtle. This result reinforces the idea that waving and skewing represent two separate phenomena, and that gravity is not a mechanistic part of the basic waving and skewing processes.

Lead authors Anna-Lisa Paul and Robert Ferl commented "Although plants use gravity as an orientating tropism on the Earth's surface, it is clear that is neither essential for root orientation, nor is it the only factor influencing the patterns of root growth. It seems that other features of the environment are also required to ensure that a root grows away from the seed, thereby enhancing its chances of finding sufficient water and nutrients to ensure its survival."

Explore further: Getting to the root of nutrient sensing

Related Stories

Getting to the root of nutrient sensing

June 14, 2010

New research published by Cell Press in the June 15th issue of the journal Developmental Cell, reveals how plants modify their root architecture based on nutrient availability in the soil.

Gardening in Space with HydroTropi

January 19, 2011

(PhysOrg.com) -- Plants are fundamental to life on Earth, converting light and carbon dioxide into food and oxygen. Plant growth may be an important part of human survival in exploring space, as well. Gardening in space has ...

Growing knowledge in space

December 1, 2011

Plants are critical in supporting life on Earth, and with help from an experiment that flew onboard space shuttle Discovery's STS-131 mission, they also could transform living in space.

New tool offers unprecedented access for root studies

December 20, 2011

Plant roots are fascinating plant organs – they not only anchor the plant, but are also the world's most efficient mining companies. Roots live in darkness and direct the activities of the other organs, as well as interact ...

Why do plant roots grow down and not up?

March 8, 2012

(PhysOrg.com) -- It is essential for roots to grow down so they can explore the soil and maximise their water uptake. But how they know that is a question that has fascinated scientists since Darwin. Now scientists led by ...

Recommended for you

Research advances on transplant ward pathogen

August 28, 2015

The fungus Cryptococcus causes meningitis, a brain disease that kills about 1 million people each year—mainly those with impaired immune systems due to AIDS, cancer treatment or an organ transplant. It's difficult to treat ...

Genomes uncover life's early history

August 24, 2015

A University of Manchester scientist is part of a team which has carried out one of the biggest ever analyses of genomes on life of all forms.

Rare nautilus sighted for the first time in three decades

August 25, 2015

In early August, biologist Peter Ward returned from the South Pacific with news that he encountered an old friend, one he hadn't seen in over three decades. The University of Washington professor had seen what he considers ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

gmungra
not rated yet Dec 10, 2012
It's almost as if the plant waves and skews its root to help navigate the higher parts op the plant towards the source of light. Much like the aerodynamic use of his tail by the flying squirrel during his 'flight'. This navigational aid would likely be a similar movement with or without gravity conditions.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.