Searching for seed gold

Dr Nathan Emery meets me in the foyer of the Australian PlantBank, where a display case holds a seed bigger than my head. The seed of the coco de mer (Lodoicea maldivica), from the Seychelles off east Africa, is the biggest on the planet – half a metre in diameter and about the weight of an average eight-year-old kid.

“It’s very easy to collect those because they float on the ocean,” Emery tells me.

Other seeds are trickier to get your hands on, like the fine, dust-like seeds of orchids that might disappear with a stray breath of wind.

“It’s just incredible to see the diversity of structures of seeds – the shapes, the colours, the size variation,” Emery enthuses.

A passion for plants and a penchant for challenge seems to be a requirement for the scientists at PlantBank, a seed bank and conservation research centre in the Australian Botanic Gardens at Mount Annan, Sydney.

“Seed bank” might bring to mind the so-called Doomsday Vault on Svalbard, designed to preserve the world’s crops in case of cataclysm. But the Vault is like a hard drive – a back-up of genetic material drawn from active seed banks around the world.

Australia is home to a network of seed banks, from the Alice Springs Desert Park to the Australian Grains Genebank to the South Australian or Tasmanian Seed Conservation Centres, many of which – including PlantBank – are also active hubs of plant research.

“Some days we’ll be out doing field work, making seed collections or monitoring threatened plants,” says Emery, whose job title is Restoration Biology Officer. “Other days, we’ll be in here conducting lab experiments on the material we bring back.”

This is becoming an urgent task as the country rapidly warms. Already, increased heatwaves, flooding, droughts, wildfires and pest outbreaks are affecting the health of mature plants across Australia, but the team at PlantBank is also studying how rising temperatures may hinder seeds from germinating.

To this end, the facility is equipped with a suite of interesting technology, from thermogradient plates to cryopreservation tanks, and we’re headed behind the scenes to check them out.

Seed searching

The first stop on our tour is the drying room, a cool space with rows of racks loaded with hand-labelled calico bags and paper packets. When seeds come in from the field, this is where they’re put.

“[The room] is capped at 15°C and 15% relative humidity,” Emery says. “That’s been shown to be to be most effective at drying down the seeds to about 5% moisture content.”

How many seeds are collected in the field depend on the species and the availability.

“For threatened species, we tend to not collect more than 10 or 15% of the available seed in any given year,” he says. “But we try to collect from as many individuals as possible to maximise that genetic variability.”

Sometimes, such as for endangered Persoonia species, that’s a few dozens or few thousands; sometimes, for species like terrestrial orchids, that’s millions.

Once they’re dry, the seeds head across the hall to the processing lab, and so do we.

“This is where we bring the collections for cleaning and viability checks,” Emery says. “We’ll use a series of sieves which have different hole diameters to separate a lot of the larger material – so sticks, leaves, things like that.”

He shows me the high-tech devices hanging above the lab benches. Some look suspiciously like pasta strainers, possibly purchased directly from the supermarket.

There are also slightly higher-tech seed-sorting machines, including a zigzag aspirator that uses suction and fans to sort by density.

Then, the seeds are X-rayed to check their viability – that is, if they contain embryos.

As he shows me the dishwasher-sized X-ray machine, Emery tells me that researchers used to slice into a sample of seeds to see what percentage are empty – either naturally or from insect predation. But cutting a seed renders it useless for storage.

“When you’ve got a threatened species or collection with very few seeds in it, every seed counts,” he says.

The PlantBank deep freeze

The seeds are then packaged into vacuum-sealed foil bags and popped into the vault. About 25,000 species are held in here, kept at -18°C.

“That, combined with the 5% moisture content, maintains viability of the seeds,” Emery says. “It slows down their metabolic processes to a point that maximises their longevity.”

Species like acacias and eucalypts can be stored for decades before their viability drops. But other species are unknowns; collections are tested every five to 10 years to check whether it’s time to head back out into the field for more.

But there’s a catch. Not all seeds can be dried and frozen.

For some, this method of preservation mimics their natural processes, but about 10% of species can’t be dried out. For example, rainforest seeds contain too much moisture and oil content to be dried and frozen effectively. Some plants, like ferns, don’t even produce seeds but spores.

“They may need to be stored […] in liquid nitrogen, so cryostorage,” Emery says. “Or they may need to be maintained as tissue culture collections.”

We head next to the tissue culture room: a bright, clean lab lined with metal racks, holding hundreds of jars with plants growing in variously coloured gel-like substances. Each looks like a tiny, one-species terrarium.

Emery introduces me to Lyndle Hardstaff, who is doing her PhD in cryopreservation at Curtin University. She shows me the species she’s growing, including lilly pillies, aniseed myrtle, native guava and macadamia.

“We take cuttings, sterilise them and put them in an agar media to which we add various nutrients – anything that they would normally get out of the soil,” Hardstaff explains.

After four to 20 weeks, the cuttings are trimmed again and put into fresh jars – a tedious, time consuming job.

“If you’re able to store seeds in orthodox conditions, it’s easier,” Emery says.

“So much easier,” Hardstaff says, with the laugh of someone who’s spent hundreds of hours transferring cuttings.

Her goal is to move her specimens into the cryopreservation facility, where they’ll be frozen in nitrogen vapour.

For preserving wild species, this is still unknown territory.

“We use all the same techniques as they use in IVF and artificial insemination,” Hardstaff says. “All of that work that was done on animals, we’re now applying to plants.”

The agricultural industry has been using this technique for over 30 years, she adds: “And now finally, we’re moving into the wild species.”

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We enter the dim, shed-like cryopreservation room. A large silver vat, about as tall as Hardstaff, occupies the far corner. A lot of “tetrising” is required to fill it, she explains: tiny pieces of plants are placed in vials, which are then arranged in boxes, which are stacked in vertical racks and lowered into nitrogen vapour – and frozen at temperatures between -192 to -194°C.

Whole seed packets might go in, or a seed embryo, or a shoot tip.

“10% of the seed bank collection, they now try to store in here as well,” Hardstaff says.

In theory, these could stay frozen indefinitely.

“That temperature is low enough that it stops all metabolism. But obviously, because we don’t have the processes to cool things down and bring them out 100% yet, there’s still a little bit of testing going on.”

Beating the heat

PlantBank’s collections are an insurance policy against extinction, but they’re also available to be used for research, either at PlantBank or by request from other scientists around the country.

Emery’s currently looking at how native seeds will be affected by rising temperatures. For most species, we don’t know the full range of temperatures at which they’ll germinate – some might be fine across dozens of degrees, while others may have tiny windows of opportunity.

To identify species most at risk, Emery and team are using a thermogradient plate: an aluminium square about a metre in diameter, which is heated along one edge and cooled along the perpendicular edge. This creates a gradient of temperatures, from 5°C at one corner up to 40°C or higher at the opposite corner. If you flick a switch, the temperature along one edge flips.

“We can essentially replicate a day-night cycle, where you’ve got hotter temperatures in the day and cooler temperatures at night,” Emery says. “It’s a really powerful way for us to get a huge amount of data in a short space of time.”

Seeds are placed in petri dishes along the temperature gradient – including at temperatures outside their normal range – and monitored to see when and if they germinate.

Their results can be extrapolated into the future using predictive climate models.

By repeating this for a range of species, Emery hopes to identify the most vulnerable – the ones whose seeds will completely fail to germinate under future scenarios – and so hit the ground running in conservation and restoration efforts.

The next step is to build a network of seedbanks and research institutions across Australia to help with this research – “because species don’t stop at geopolitical borders,” Emery says.