Scientists are currently trying to find out if plants have sixth sense. While it is debatable as to whether plants possess the five senses common to humans (basically, sight, smell, taste, hearing and touch), they do have a distinct perception of gravity, which in turn enables them to grow upright. As part of the Plant Gravity Sensing study, researchers are studying plants, cultivated in space, to discern how they sense the direction of their growth, without gravity.
Gravitropism, which refers to the turning of plants in response to gravity, takes places in two ways: first, the roots grow downward, in the direction of the gravitational force, and therefore, exhibit positive gravitropism. Secondly, the stem extends upward, in the direction of sunlight (known as phototropism) and thus, shows negative gravitropism. To see if a plant’s “gravity sensor” functions, even in the absense of any gravitational pull, a team of scientists, working with the Japanese Aerospace Exploration Agency, will soon conduct an experiment to determine how plants grow in space.
For the research, the team has chosen to study the processes of cell formation, and development, in Arabidopsis thaliana or thale cress. A small flowering plant found all over Eurasia, thale cress’ extremely simple genetic makeup allows the researchers to examine its various mechanisms, in great detail. Another important feature that changes in response to gravity is the plant’s calcium concentrations. With the help of a centrifuge, the scientists will investigate how the calcium level, in the cells of a plant grown in microgravity inside a spacecraft, alters when exposed to Earth’s 1g environment. Speaking about the study, Hitoshi Tatsumi, of Japan’s Nagoya University, said:
Plants cultivated in space are not experienced with gravity or the direction of gravity and may not be able to form gravity sensors that respond to the specific direction of gravity changes
While the exact mechanism behind gravitropism is still unclear, the scientists believe that it has something to do with amyloplast, a type of organelle, present in plant cells, which is responsible for the synthesis and storing of starch. These particles assemble in the direction of gravity, thereby triggering other mechanisms, including the increase in calcium concentrations. Such processes, together, determine the plant’s growth-direction, in relation to gravity.
According to the team, the research could provide valuable insight as to how the gravity-sensing mechanisms, of plants, can be modified for higher crop yields, on Earth. Furthermore, it could allow astronauts to grow their own food, during deep space missions. Tatsumi added:
We may design plants that respond to gravity vector changes more efficiently than wild ones. These plants will recover from collapse by winds or flood more rapidly than wild ones. Thus, the agricultural output of the designed plants will be greatly increased, which may solve, in part, the shortage of crops in the near future.