Plant seeds are fascinating structures.Some are barely visible to the naked eye, others grow as big as footballs. Some can fly, others have to be eaten to spread. If seeds are kept cool, dark and dry, they often remain germinable for years. This is ensured by growth-inhibiting plant hormones that control the time of germination. This is important because the survival of the young plant depends on it. If it is too cold, it dies. If nutrients are lacking, it atrophies. A Swiss team led by scientists from the University of Geneva has now identified the internal thermometer of seeds that can delay or even block germination if temperatures are too high for the future seedling. They report on this.
The group led by Luis Lopez-Molina, Professor of Plant Sciences at the University of Geneva, investigated the mechanisms of germ control of Arabidopsis thaliana, a plant species belonging to the cruciferous family (Brassicaceae) and used as a model organism in many research projects.In order to understand the recognition mechanisms behind thermal inhibition, the scientists investigated phenomena that are already well understood in very young plants. The idea is that they may resemble the processes sought in seeds.
In fact, young plants also perceive temperature changes. If it gets warmer, the stem grows faster. This adaptation is similar to the reaction of one plant that is in the shade of another: it lengthens to escape the shadow. Such mechanisms are controlled by a light- and temperature-sensitive protein, phytochrome_ B, which normally acts as a growth brake for the plant. If the temperature rises by 1 to 2 degree, becomes the phytochrome_- B inactivates faster, so that it slows down the growth of the plant less strongly.
To find out if phytochrome_- B also plays a role in thermal inhibition during germination, the researchers dissected the seeds to separate the two tissues inside: the embryo, from which the young plant emerges, and the endosperm, which as nutrient tissue supports and controls the germination of the Arabidopsis seeds.They found that embryos that have been deprived of the endosperm cannot stop their growth at too high temperatures. As a result, the seedlings die.
«The heat inhibition in Arabidopsis is therefore not autonomously controlled by the embryo, but by the endosperm,» explains Urszula Piskurewicz, biologist and first author of the study, according to a statement from the University of Geneva. We have thus demonstrated a new essential function of this tissue.»In other words, without endosperm, the embryo in the semen would not notice that the temperatures are too high and would start germination.
This mechanism of so-called thermoinhibition is also important for agriculture in a warming world, the scientists write in their study. A better understanding of how light and temperature trigger or delay seed germination could help optimize the growth of plants exposed to extreme climates.
Source — https://www.spektrum.de/news/inneres-thermometer-bestimmt-wann-pflanzensamen-keimen/2117256