Section of a seed of Arabidopsis thaliana, a design organism widely used in plant sciences. Credit: UNIGE/ Sylvain Loubéry
Researchers have discovered the mechanisms by which the seed chooses to remain in “hibernation” or to activate its germination depending on the outdoors temperature.
Germination is an important phase in the life of a plant as it will leave the phase of seed resistant to different environmental restrictions (climatic conditions, absence of nutritive elements, and so on) to become a seedling much more susceptible. A Swiss group, led by scientists from the University of Geneva (UNIGE), has discovered the internal thermometer of seeds that can postpone or even block germination if temperatures are too high for the future seedling.
Newly formed seeds are dormant: they are unable to germinate. After a couple of days (or even months, depending on the types), the seeds awaken and acquire the capability to sprout during the beneficial season for seedling development and new seed production. Non-dormant seeds can still choose their fate.
Germination is a crucial stage in the life of a plant as it will leave the phase of seed resistant to various environmental restrictions (climatic conditions, absence of nutritious elements, and so on) to end up being a seedling much more vulnerable. A Swiss team, led by scientists from the University of Geneva (UNIGE), has discovered the internal thermometer of seeds that can delay or even block germination if temperature levels are too high for the future seedling. Newly formed seeds are inactive: they are unable to sprout. After a couple of days (or even months, depending on the types), the seeds awaken and get the capability to germinate during the favorable season for seedling growth and new seed production. A better understanding of how light and temperature trigger or delay seed germination might undoubtedly help optimize the development of plants exposed to a large variety of climatic conditions.
An essential protein: phytochrome B
The group of Luis Lopez-Molina, teacher at the Department of Plant Sciences of the Faculty of Science of the UNIGE, is interested in the control of germination in Arabidopsis thaliana, a plant types coming from the Brassicaceae household and used as a design in many research tasks. To understand the detection systems that permit seeds to trigger thermo-inhibition, researchers checked out the track of phenomena currently described and rather similar in young plants, i.e. at an advanced stage of advancement.
Indeed, temperature level modifications are also viewed by seedlings, in which a minor increase in temperature promotes stem development. This adjustment resembles the one observed when a plant finds itself in the shadow of another: it extends to get away the shadow in order to expose itself to the sunlight which is more favorable for photosynthesis. These variations are discovered by a protein conscious light and temperature, phytochrome B, which generally acts as a brake on plant growth. A boost of 1 to 2 ° C promotes the inactivation of phytochrome B, which makes it less effective in preventing growth.
An internal thermometer
To comprehend whether phytochrome B likewise contributes in thermo-inhibition during germination, the authors dissected the seeds to separate the 2 tissues inside the seed: the embryo (which will offer the young plant) and the endosperm (nourishing tissue that also manages germination in Arabidopsis seed). Unlike embryos grown in contact with the endosperm, the scientists discovered that embryos denied of their endosperm are not able to stop their growth under too expensive temperatures, which leads to their death.
” We found that thermo-inhibition in Arabidopsis is not autonomously managed by the embryo but carried out by the endosperm, revealing a new important function for this tissue,” explains Urszula Piskurewicz, scientist at the Department of Plant Sciences of the UNIGE Faculty of Science and first author of the study. “In other words, in the absence of endosperm, the embryo within the seed would not perceive that the temperature levels are too high and would start its germination, which would be fatal.”
Enhancing crop germination
Thermal inhibition of germination is a new example of the influence of climatic variations on particular cyclic phenomena in plant life (germination, flowering, etc). “This characteristic is anticipated to have an influence on species distribution and plant farming and this effect will be greater as temperatures increase worldwide,” reports Luis Lopez-Molina, the research studys last author. A much better understanding of how light and temperature trigger or hold-up seed germination could indeed assist optimize the growth of plants exposed to a large range of climatic conditions.
Reference: “The Arabidopsis endosperm is a temperature-sensing tissue that executes seed thermoinhibition through phyB” 7 March 2023, Nature Communications.DOI: 10.1038/ s41467-023-36903-4.