If we knew more about how light and temperature speed up or slow down seed germination, we could help plants grow better in a wide range of weather conditions.

A UNIGE team has uncovered the processes by which the seed determines whether to stay in “hibernation” or to germinate depending on the temperature outside.

Germination is an important stage in the life of a plant because it transitions from the seed stage, which is resistant to numerous environmental restrictions (climate, lack of nutritional materials, etc.), to the seedling stage, which is considerably more fragile.

The timing of this transformation determines the viability of the young plant. Hence, it is crucial that this period be carefully managed.

Researchers from the University of Geneva (UNIGE) in Geneva, Switzerland, have shown that seeds include an internal thermometer that, if temperatures rise too high for the future seedling, might hinder or even prevent germination.

These findings have been published in the journal Nature Communications.

Seeds that have recently formed are in a dormant state, which means they cannot start to grow.  When the time is right for the seedlings to develop and produce new seeds, the dormant seeds awaken after a few days (or even months, depending on the species).

Non-dormant seeds may still control their destiny, nevertheless. For instance, if a non-dormant seed is abruptly exposed to temperatures that are too high (more than 28 degrees Celsius), this might prevent the seed from germinating. This temperature-induced inhibitory mechanism (thermo-inhibition) enables very precise control.

A change in temperature of just one to two degrees Celsius may, in fact, delay the germination of a seed population and, as a result, enhance the likelihood that subsequent seedlings will survive.

Phytochrome B

The lab of Luis Lopez-Molina, a professor in the UNIGE’s Department of Plant Sciences on the Faculty of Science’s Science Campus, is investigating how to regulate germination in Arabidopsis thaliana, a member of the Brassicaceae family of plants that serves as a model organism in a wide variety of scientific investigations.

In order to learn about the processes of detection that enable seeds to initiate thermo-inhibition, researchers have followed the trail of phenomena previously reported and relatively comparable in young plants, i.e. at a more developed stage of growth.

Indeed, seedlings are also sensitive to temperature shifts; a little rise in temperature stimulates stem development. This adaptation resembles the one seen in plants when they are in another plant’s shade: they extend to get out of the shadow and expose themselves to the sunshine, which is better for photosynthesis.

Phytochrome B, a protein sensitive to light and temperature that typically slows plant development, is able to detect these differences. Phytochrome B is inactivated by a temperature rise of 1 to 2°C, which reduces its ability to inhibit growth.

A thermometer inside

To find out if phytochrome B also affects thermo-inhibition during germination, the authors cut open the seeds and separated the embryo (which will become the new plant) and the endosperm (nourishing tissue that also controls germination in Arabidopsis seed).

Study discovered that embryos that grow without their endosperm can’t stop growing when the temperature gets too high, which kills them. This is different from embryos that grow with their endosperm.

‘‘We found that thermo-inhibition in Arabidopsis is not autonomously controlled by the embryo but implemented by the endosperm, revealing a new essential function for this tissue,’’ remarks first author Urszula Piskurewicz. ‘‘In other words, in the absence of endosperm, the embryo within the seed would not perceive that the temperatures are too high and would begin its germination, which would be fatal’’.

Maximizing the Success of Seedlings

An emerging example of the impact of climate change on some cyclic events in plant life (germination, flowering, etc.) is the restriction of germination caused by heat.

‘‘This trait is expected to have an impact on species distribution and plant agriculture and this impact will be greater as temperatures increase worldwide,’’ adds last author Luis Lopez-Molina. 

If we knew more about how light and temperature speed up or slow down seed germination, we could help plants grow better in a wide range of weather conditions.

Source: 10.1038/s41467-023-36903-4

Image Credit: Getty