Conclusion
The study emphasised the plants' difficulties to cope with a low gravity. Little work has already been done about microgravitropism, and even on gravitropism. However, this is a very important field. Just think about the fact that mankind plans to conquer other planets, and that a knowledge about space agriculture is absolutely necessary for that purpose. See comments in NASA reports: " Plants will be a key part of the biogenerative systems that will be required to ensure human survival during long-term space missions or on extraterrestrial bases.(....) A critical question is whether plants can grow and reproduce well enough to make long-term crop production practical in a reduced gravity environment. ".
Modern studies on microgravitropism remain uncompleted and even contradictory.
" Definite knowledge of the effects of microgravity at all stages of life cycle of plants and from the level of the organism to the level of subcellular and biochemical activity remains extremely limited. (...). There is limited information about plant development and reproduction in microgravity. The data about flowering and seed formation in space are often conflicting. ".
Nevertheless, there has already been a remarkable evolution in the theories about microgravitropism: The first theory was based on the hypothesis that starch molecules called statolithes were present in the roots of the plants, and that the quantity of statolithes was in relation with the plants' sensibility towards a low gravity. According to that theory, gravity makes statolithes move into the roots, which causes the migration of glucidic components into the stem, and as a result, due to osmotic pressure, the stem grows skywards. However, this theory was unable to explain some of the microgravitropic effects.
Another theory, which is believed to be correct, is based on the effects of a vegetal hormone called auxine. Other, still uncompleted studies are based on effects related to the DNA sequence, on quantum theory,.....