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11. Sept. 2026
What happens inside a seed when a plant is exposed to high temperatures for a prolonged period? In oilseed rape, the embryo begins to develop faster, while its protective coat fails to keep pace. As a result, the seed coat can rupture and the seed may start to germinate prematurely, making it unsuitable for long-term storage or future sowing. Scientists from CEITEC Masaryk University and their colleagues have now described the mechanism behind this phenomenon. Finding the answer involved several dead ends, a conversation at a scientific conference, and collaboration between biologists and physicists.
A seed consists of several parts whose development needs to be carefully coordinated. Inside, the embryo – the developing plant – grows protected by the seed coat, the seed’s outer layer. According to the new study, prolonged high temperatures disrupt this coordination.
Researchers from Hélène Robert Boisivon’s team at CEITEC Masaryk University grew oilseed rape (Brassica napus) at 21 °C and under conditions in which the temperature reached 32 °C for part of the day. Embryos exposed to the higher temperature were approximately four days ahead in their development and more than twice as large at the same age. The seed as a whole, however, did not grow at the same pace. The seed coat ruptured in approximately half of the seeds exposed to high temperature. “Growth of the different tissues inside a seed needs to be well synchronised. At high temperature, the embryo develops faster, while the seed coat cannot adapt sufficiently. This disrupts the mechanical balance, and the seed coat can eventually rupture,” says Unnikannan Prabhullachandran from CEITEC Masaryk University, first author of the study.
The strength of the seed coat is important for what happens to the seed next. It protects the embryo from external conditions and pathogens. If a seed starts to germinate while still on the plant, it begins to use up its reserves, and the process cannot be reversed. Such seeds are unsuitable for long-term storage or future sowing.
But the researchers did not arrive at this explanation directly. Premature seed germination is commonly associated with a loss of dormancy – the natural resting state of a seed – and hormonal imbalance. The team initially investigated these possibilities, but the results did not support their original assumptions. They therefore turned their attention to the faster-growing embryos and found that at high temperatures, the layers of the seed coat were thinner and the coat as a whole was more compliant. “For a long time, we were missing one piece of the puzzle. We were looking for a biological explanation, but eventually realised that we also needed to look at the seed as a physical system. That was when the results started to fall into place,” says Hélène Robert Boisivon.
An important clue came from a conversation at a conference and a reference to work by Hardy Rolletschek’s team at IPK Gatersleben [1]. In their research on oilseed rape, the team had used silicone tubes to mechanically constrain growing siliques – the fruits of oilseed rape in which the seeds develop. The Brno researchers tried the method under high-temperature conditions – and the mechanical support indeed reduced the number of seeds with ruptured seed coats.
This brought physics into the research as well. Together with colleagues from the Faculty of Science at Masaryk University, the team measured the mechanical properties of the seeds using nanoindentation, a method that examines how a material responds to pressure from a very small probe. The measurements supported the physical hypothesis: the surface of seeds developing at high temperature was softer, while the seed coat as a whole was more compliant.
Previous work by the team involving three spring oilseed rape cultivars also linked high temperatures and premature germination with reduced seed viability and changes in oil quality. The current study examined one oilseed rape cultivar under controlled conditions and primarily provides new fundamental insight into how high temperatures disrupt the coordination between the growing embryo and its protective seed coat.
The results were published in Plant Stress.
[1] https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.19990
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