It’s one thing having billions of seeds stored safely for future research and conservation. Converting these seeds into healthy seed-bearing plants for restoration is another challenge!
At the Millennium Seed Bank (MSB), germination testing is a key process for long-term seed quality monitoring and, importantly, it enables us to find the ideal conditions to promote growth. Some species can be very tricky to crack!
For many plants, seeds are the main form of reproduction, enabling genes to be shared, moved around and passed down to future generations. Consequently, it is crucial that seeds germinate in the right place, at the right time to maximise the chance of growing into a healthy, seed-producing plant.
The primary requirement to kick off the germination process is moisture. Internal water content naturally decreases in ripening seeds, and in our previous blog, we explained the importance of additional drying for long-term seed storage. Returning seeds to a moist environment fires up metabolic processes in re-hydrated cells and seeds pick up where they left off!
At this stage, temperature is key. Each species has a preferred temperature range that will prompt germination. For some, the range is broad, and seeds germinate easily. Others require more specific conditions to activate growth.
Living seeds that do not germinate even under ideal temperature and moisture levels are said to be dormant. Dormancy prevents seeds from germinating at a time when conditions might not be suitable to support growth throughout the plant’s life cycle – in warm, moist autumn weather just before a cold, dark winter, for example. Dormant seeds must lose their dormancy before germination can occur. Dormancy may be controlled internally (endogenous) or externally (exogenous). Endogenous dormancy is controlled by the embryo (which will become the plant) and endosperm (nutrient storage tissue) inside the seed, whereas exogenous dormancy is imposed by a hard, impermeable seed coat.
Endogenous dormancy is typically lost over time in response to seasonal temperature changes. Seeds of many UK summer annuals cannot germinate before experiencing a cold stratification period over winter. This promotes spring germination, when increasing temperatures signal that upcoming summer conditions are perfect for growth. In some cases, several years of seasonal temperature changes may be required before seeds will germinate. In the lab, we can accelerate the process by conducting seed surgery!
This is how we are using a small wild collection of critically endangered red hemp-nettle (Galeopsis angustifolia) to produce a much larger harvest of regenerated seed for Colour in the Margins. The seeds display varying levels of endogenous dormancy, so would germinate irregularly over multiple growing seasons if left to their own devices. This is a useful strategy in the wild, but to produce a large genetically-diverse seed collection, we need to collect from as many plants as possible, requiring lots of seed germination now! Previous MSB research has revealed that both the seed coat and endosperm must be removed to reliably promote high levels of red hemp-nettle germination. It’s fiddly work, but by using forceps and a scalpel under a microscope, it is possible to remove the 2mm-long embryo from the rest of the seed. The embryo is then able to germinate on agar jelly in our incubators, and usually grows into a healthy seedling.
The challenges to establishing a regenerated population don’t end once seeds have germinated…nurturing healthy seedlings to maturity requires determination and innovation! Learning from past experiences (positive and negative!) is crucial for the ongoing development of propagation protocols for even the trickiest of wild species!
Our next blog post will delve into the highs and lows of cultivating seedlings in the nursery, where we’ll take a closer look at our expanding population of spreading hedge-parsley, another priority species for Colour in the Margins.
UK Native Seed Hub Assistant - MSB.
Would you like to help this incredible species? There are numerous ways in which you can:
- Why not volunteer for Back from the Brink? Check out our events page for opportunities near you.
- Help us to spread the word of this species, and the others we will be helping over the next 3 years, by sharing our message across our Twitter, Facebook, Instagram and YouTube pages. Follow us: @naturebftb.
- Finally - help support the work we do across England by donating. Our impact will be greater with your help.