The idea of the project
My study is about microgravitropism in sunflower seedlings. Microgravitropism is the plants' response to a low gravity. The first step to the project was the reading of an article published in the " Amateur Scientist " columns of the Feb.96' issue of Scientific American, under the title " Growing Seedlings at less than 1 G " (see a.i. I). The article briefly described gravitropism in some plants. It seemed very interesting to me to investigate that subject, for I had heard how harmful rapid variations of gravity can be on human beings (loss of consciousness,...).
I also wanted to know how plants would react when gravity changes because research projects on microgravitropism are gaining importance with the progress of space exploration.
My tutor, Mr Gérard, helped me to build a clinostat which is a device to simulate various gravitational forces, and I am pleased to acknowledge my indebtedness for his help.
Preliminary Study
First of all, I tried to figure out which plant would fit the best for my study. Among 40 plants (including cress, beans, Soya, salad, pumpkin, radish, peas,...), sunflowers seemed to be the ones that grow the fastest, without being too fragile.
Afterwards, I studied the seedlings' reactions to the actual Earth's gravity (1 G). Therefore I fixed the stem onto a plastic plate and I covered the plant with a glass case (see Figure 1). After three hours, the seedlings had managed (in a darkened room , to eliminate effects of phototropism) to grow upwards and to move from the horizontal position to a vertical position).
Figure 1. The seedlings' reaction to the actual Earth's gravity (1 G).
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This shows that the Earth's gravity constantly affects the plants' position. It forces the plants to stand the way we find them in nature, with the stem reaching upwards and the roots growing downwards.
Structure of the Study
Due to the lack of specific material for a biochemical study, I only concentrated my work on morphological aspects of the graviperception. (I plan, however, to obtain the necessary material from a university lab, in order to add a second part to my project).
My study was divided into two parts:
A) The first study focused on the germination at a low gravity.
B) The second study focused on the minimal gravity required by the seedlings to grow normally, and on the plants' reactions to a lower gravity.
I imagined that a low gravity would disturb the plants, which would loose their orientation. But the basic question remained: how would that actually affect the plants' germination and their growth ?