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How can seeds germinate after thousands of years of dormancy?

Q: If a seed is planted in the ground even after lakhs of years, the plant will sprout.. But how did that seed manage to hide life within itself for all these lakhs of years? Can you tell me? (The clue is in the Bhagavad Gita).

Krishna: You are giving clues too to me on how to answer this question! :) If you know the answer why did you ask me in the first place? You should have answered it yourself using Holy Books.

But I can give you the right answer.

There are various reports on this subject. There have been several seeds known at different times as the oldest viable seed.

1. Plants that were grown from seeds buried in permafrost for nearly 32,000 years. The seeds were discovered on the banks of the Kolyma River in Siberia. The river is constantly eroding into the permafrost and uncovering frozen Pleistocene relics. Upon their discovery, researchers took the seeds and did the unthinkable - they grew them into adult plants. To date, this is the oldest resurrected plant material (1).

2. The oldest seed to germinate was a date palm seed found in the rubble of Masada, Israel, and germinated in 2005. The seed was about 2,000 years old. (2)

3. Another oldest viable seed recorded is a 1,300-year-old sacred lotus (Nelumbo nucifera) recovered from a dry lake bed in northeastern China in 1995 (3).

4. A previously unknown species of Commiphora, possibly the source of the biblical medicinal extract tsori, was successfully germinated from a single seed in 2010 and carbon-dated to between AD 993 and 1202, more than 800 years old (4)

5. The oldest viable seed that has been scientifically documented is a lupine seed that is estimated to be at least 10,000 years old. The seed was found in the Arctic Tundra and germinated in a laboratory (5).

6. 32,000-Year-Old Plant Brought Back to Life—Oldest Yet. (6)

The oldest plant ever to be regenerated has been grown from 32,000-year-old seeds—beating the previous recordholder by some 30,000 years. (Related: "'Methuselah' Tree Grew From 2,000-Year-Old Seed.")

A Russian team discovered a seed cache of Silene stenophylla, a flowering plant native to Siberia, that had been buried by an Ice Age squirrel near the banks of the Kolyma River (map). Radiocarbon dating confirmed that the seeds were 32,000 years old.

The mature and immature seeds, which had been entirely encased in ice, were unearthed from 124 feet (38 meters) below the permafrost, surrounded by layers that included mammoth, bison, and woolly rhinoceros bones.

The team extracted that tissue from the frozen seeds, placed it in vials, and successfully germinated the plants, according to a new study. The plants—identical to each other but with different flower shapes from modern S. stenophylla—grew, flowered, and, after a year, created seeds of their own.

These are recorded instances.

We don't know what else happened in Nature without our knowledge, though.

"Dormancy"* allows seeds to survive for extended periods, which can aid in seed dispersal and spread out the growth and establishment of seedlings, increasing the likelihood that some of the next generations survive if conditions are not suitable for seedling establishment. Over time, seeds lose viability, which is the ability to initiate metabolic activity, cellular growth, and germination. Seeds have many cells and tissues that die over time, and these deaths can be delayed or increased by environmental conditions the seed experiences. Very generally, small seeds, especially from weedy species and annuals are more likely to remain viable in the soil longer than larger perennial seeds. The seeds of some aquatic plants also may remain viable longer in mud because their viability is aided by the aquatic environment which remains cool and moist.

Seed dormancy** is an evolutionary adaptation that prevents seeds from germinating during unsuitable ecological conditions that would typically lead to a low probability of seedling survival.Dormant seeds do not germinate in a specified period of time under a combination of environmental factors that are normally conducive to the germination of non-dormant seeds.

An important function of seed dormancy is delayed germination, which allows dispersal and prevents simultaneous germination of all seeds. The staggering of germination safeguards some seeds and seedlings from suffering damage or death from short periods of bad weather or from transient herbivores; it also allows some seeds to germinate when competition from other plants for light and water might be less intense. Another form of delayed seed germination is seed quiescence, which is different from true seed dormancy and occurs when a seed fails to germinate because the external environmental conditions are too dry or warm or cold for germination.

Many species of plants have seeds that delay germination for many months or years, and some seeds can remain in the soil seed bank for more than 50 years before germination. Seed dormancy is especially adaptive in fire-prone ecosystems. Some seeds have a very long viability period.

The mechanisms that are thought to aid this process are :

1. Water ( moisture): It is essential, absolutely essential, for the metabolism underlying life processes to function. In principle, living cells can become sufficiently desiccated to stop metabolism without the membranes and organelles within the cell being denatured beyond recovery (when water becomes available). The resurrection plant (Selaginella lepidophylla) provides an example of the desiccation tolerance that is possible.

2. Temperature: Metabolism stops when temperatures are sufficiently and persistently below the freezing point. It’s fairly routine practice in biochemistry labs to freeze metabolically active (wet) tissues, including embryos, and store them (cryopreservation) in liquid nitrogen. When removed, they function normally. Ice crystal formation during freezing can rupture cell membranes hence kill, but a combination of gradual desiccation (slow freeze drying) and gradual lowering of temperature can prevent ice crystals forming. This may be what (rarely) happens in permafrost environments where the oldest seeds have been discovered.

3. Light: Even harsh light can degrade seeds over time. Seeds that are in darkness can lie dormant for several years.

4. Other environmental factors: Sometimes it’s a combination of prolonged moisture, ground temperature, nutrient availability, soil mineral composition, and the microbiome of the soil.

5. Natural Life span: Even under perfect conditions, seeds have a natural lifespan depending on their genes and life's cycles.

Some other causes of seed dormancy are as follows:

Seed coat impermeable to water: Seeds of families Fabaceae, Malvaceae, Convolvulaceae, Solanaceae and Chenopodiaceae contain very hard seed coats which are impermeable to water. These seeds remain dormant in soil until the impermeable layer of testa decays.
Seed coat impermeable to oxygen: In many plants such as cocklebur (Xanthium strumarium), dormancy of seeds results from the impermeability of seed coats to oxygen.
Mechanically resistant seed coat: The seeds of certain weeds such as pigweed (Amaranthus spp.) Shepard’s purse (Capsella bursa-pastoris) water plantain (Alisma spp.) remain dormant because their hard seed coat prevent any appreciable expansion of the embryo. This dormancy may persist up to 30 years.
Immaturity of the embryo: In plants such as orchids, Ginkgo biloba, and Fraxinus spp. the seed dormancy results from the immaturity of the embryos which fail to develop fully by the time of the seeds are shed.
Germination inhibitors: Sometimes the dormancy of seeds results due to presence of certain inhibitors e.g. phthalide, ferulic acid, abscisic acid, dehydroacetic acid and parasorbic acid.
Chilling requirements: In certain plants such as apple (Malus pumila), rose (Rosa spp.), peach ( Prunus persica) etc. seeds remain dormant because they require low temperature for germination which is fulfilled by nature during winter.
Light sensitive seeds: Light sensitive seeds are called photoblastic. The seeds of plants such as lettuce (Lactuca sativa) Shepard’s purse (Capsella bursa-pastoris), tobacco (Nicotiana tobaccum) and tomato (Solanum lycopersicum) are positively photoblastic while seeds of Helloborus, Nigella and Silene are negatively photoblastic.

Sometimes grass seeds lie dormant for several years. What are the reasons for this dormancy?

There are many factors that influence grass seed germination.

Fire: Seeds exposed to smoke or fire are primed to germinate much more readily. This adaptation allows them to take advantage of the clearing created by wildfire. So seeds are smoke sensitive.

Time (internal clocks): Wheat generally doesn't germinate as well immediately after it's harvested. Historically some varieties were particularly bad at this when farmers were early seeding it back into the ground only 30 days or so after harvest. The seed industry term "sweating" is used to describe seed that has been intentionally stored for long enough for the seed to count out its internal clock and achieve full germination rate.

Conversely, there will always be a percentage of seeds that absolutely refuse to germinate in the first season. This is a population survival strategy in case an adverse event wipes out everything. There will still be survivors in the soil bank to reestablish a population. This is the strategy that the grassy weeds we struggle with evolved to evade our control methods. And it's a strong remnant behaviour in secondary crops like rye and oats, which were once wild and readily go feral again.

Some rye seeds lie dormant for over 5 years in the ground before reemerging.

Soil Cues: Even when seeds have sufficient moisture for germination they are very sensitive to the presence of other things in the soil. Seeds particularly do not like to be placed into soil mixed with undecomposed vegetation. This is a smart strategy, as they are at greater risk of desiccation there. They likely detect the same chemicals surrounding them that they do when still within the unthreshed head, and resist germinating. Farmers call this "hairpinning" - when seeds are folded within a tuft of straw tucked into soil in turn. We set up and alter seeding implements to prevent it, or if it's not preventable we must seed at a higher rate to offset the increased mortality.

Molecular mechanisms of dormancy:

Regarding the molecular mechanism, the "canonical" chemical signal comes in form of giberellins (or GA, for giberellic acid), a class of plant hormone. Dormancy is maintained by a different hormone, abscissic acid (ABA), and these two hormone signaling pathways regulate each other antagonistically. Mutually antagonistic regulation is a type of positive feedback loop, where the increase in strength of one signal (here, GA) decreases the strength of another signal (here, ABA). Because ABA itself suppresses GA, the buildup in GA becomes self-reinforcing by removing the ABA that was suppressing its buildup. Once a certain threshold of GA concentration is reached, dormancy is broken and the seed germinates. Within a brief period of time, the germination process is reversible.

The initiators for the buildup of GA are numerous and vary by plant species. Also, GA is just the signal for germination: its presence triggers the expression of genes that do the actual work involved, such as breaking down the seed coat and turning stored chemical energy in the endosperm into shoot and root biomass.

Finally, it's important to note that the system described here is highly simplified and probably not applicable to all plants. Hormone classes and their broad functions seem to be relatively well conserved across plant lineages, but the functions of each phyotohormone class are notoriously diverse. ABA, as well as being an inhibitor of germination, is involved in virtually every single stress response, among other important processes. Ethylene (most well known for its role in fruit ripening) has also been shown to promote germination, which helps the seed sense that it's underground, as ethylene is a gas whose diffusion away from the seed will be slower within the soil rather than in the open air.

So seed can sprout even after thousands of years because of a process called "dormancy," where the seed remains inactive until environmental conditions are ideal for germination, allowing it to survive for long periods in a protected state, often within a hard seed coat, and with the necessary nutrients stored inside to initiate growth when conditions are right, like proper temperature, moisture, and light; essentially, the seed "waits" for the perfect moment to sprout, which can sometimes be after thousands or even millions of years, depending on the species and preservation conditions.

Key points about seed dormancy:

Protective mechanisms:

The seed coat acts as a barrier, preventing damage from external factors like extreme temperatures or drying out.
Environmental cues:

Many seeds require specific environmental cues like cold stratification (exposure to cold temperatures) or fire to break dormancy and initiate germination.
Examples of long-lasting seeds:

Lotus seeds: Some lotus seeds have been documented to germinate after thousands of years.
Arctic plants: Seeds from plants found in permafrost have been known to sprout after thousands of years when thawed.

Normally seeds don't stay alive for long, though. Seeds that can do so are exceptional in several ways.

Seeds can remain viable for thousands of years due to a process called "desiccation tolerance," where they enter a state of extreme dryness, essentially putting their metabolism on hold conserving energy, which allows them to withstand harsh conditions like extreme temperatures and low moisture for extended periods, particularly when buried in environments like permafrost; this is especially true for seeds from certain Arctic plants like the Silene stenophylla (narrow-leafed campion) which have been found to germinate after thousands of years.

The key to their extreme longevity lies in the permafrost. They were found inside the frozen burrow of an Arctic ground squirrel. The state of the burrow suggests that everything froze quite rapidly. As such, the seeds remained in a state of suspended animation for 32,000 years. This is not the first time viable plant materials have been recovered from Pleistocene permafrost. Spores, mosses, as well as seeds of other flowering plants have been rejuvenated to some degree in the past but none of these were grown to maturity.

Using micropropagation techniques coupled with tissue cultures, researchers were able to grow and flower the 32,000 year old seeds. What they discovered was that these seeds belonged to a plant that can still be found in the Arctic today. It is a small species in the family Caryophyllaceae called Silene stenophylla. However, there were some interesting differences.

As it turns out, the seeds taken from the burrow proved to be a phenotype quite distinct from extant S. stenophylla populations. For instance, their flowers were thinner and less dissected than extant populations. Also, whereas the flowers of extant populations are all bisexual, individuals grown from the ancient seeds first produced only female flowers followed by fewer bisexual flowers towards the end of their blooming period.Though there are many possible reasons for this, it certainly hints at the different environmental parameters faced by this species through time. What's more, such findings allow us a unique window into the world of seed dormancy. Researchers are now looking at such cases to better inform how we can preserve seeds for longer periods of time.

Footnotes:

1. https://www.indefenseofplants.com/blog/2015/11/4/germinating-a-seed...

2. https://www.nytimes.com/2008/06/17/science/17obseed.html#:~:text=Sc....

3. Shen-Miller; Mudgett, M. B.; William Schopf, J.; Clarke, S.; Berger, R. (1995). "Exceptional seed longevity and robust growth: Ancient sacred lotus.... American Journal of Botany. 82 (11): 1367–1380. doi:10.2307/2445863. JSTOR 2445863.

4. Katie Hunt (3 October 2024), Lost biblical plant with medicinal properties resurrected from 1,000-year-old seed, retrieved 4 October 2024

5. https://www.toppr.com/ask/question/this-is-an-example-of-a-very-old...

6. https://www.nationalgeographic.com/science/article/120221-oldest-se...

* https://en.wikipedia.org/wiki/Oldest_viable_seed

** https://en.wikipedia.org/wiki/Seed_dormancy

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