Plants and Gravity
So, do plants grow the same way in space as they do on Earth? Scientists are learning more about how plants grow in space every day. Gravity plays an important part in plant growth. Remember when we learned in Mission 1 about gravity, the force of attraction that keeps our feet firmly planted on the Earth? We know which way is down because of gravity's pull on us. Well, plants also use gravity to know which way is down. The root tips of plants have special starch grains inside called statoliths . These grains are heavy. They fall to the bottom of the root tip cells and act as a signal. They tell the plant which way is down. If you tip a plant on its side, the heavy grains in the root tip would again be pulled down by gravity, and this would tell the plant which way is down. The root would then start growing in that direction.
Click here to see a video showing gravitropism.
(The video is courtesy of Roger Hangarter's lab)
In the same way that roots use gravity signals to grow downward, shoots use these signals to grow upward. Shoots also use light to tell which way to grow. Shoots grow towards light, and away from gravity. These plant movements are called tropisms ( gravitropism for gravity and phototropism for light). Scientists want to understand the signals inside a plant that help the shoots to know to grow up and the roots to know to grow down. In spaceflight, where the plant does not have gravity to help the roots and shoots to orient , plants usually get confused and grow in a mixed-up way. In a microgravity environment, the starch grains should float around randomly, just like astronauts do. Instead, scientists have found that they bunch together. Why? It's part of the mystery. Maybe one day you will help to solve it!
Entry 16 : We know that in microgravity, plants get confused and grow in random directions. So, on the Moon where gravity is only 1/6 of that on Earth, how do you think plants might grow? Write what you think in your Agronaut Log.
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