Have you ever opened up a fruit and found seeds sprouting inside?
What causes seeds to germinate prematurely?
The premature germination of seeds inside fruits, called “vivipary”, is due to hormonal imbalance or a reduced level of abscisic acid (ABA). This can happen when the fruit is under environmental stress, overripe, deficient in potassium, overfertilized with nitrogen, and mutated genetically.
In this article, we will explore the reasons behind this rather uncommon phenomenon called “vivipary”, how to prevent it, and whether you can still plant the seeds.
What is vivipary?
The phenomenon of seeds that germinate prematurely inside fruits is called “vivipary”.
Normally, when seeds develop inside a fruit, they are kept dormant and premature germination is suppressed by maintaining a balance between the abscisic acid (ABA) hormone and the gibberellin hormone.
But, when this protective system weakens, a phenomenon called vivipary happens where seed dormancy would end and the seeds inside a fruit would sprout prematurely.
The reason why plant hormones can be out of balance can be due to different types of environmental stresses, including (1) environmental stress, (2) being overripe, (3) potassium deficiency, (4) over-fertilization with nitrogen, (5) genetic mutations.
What causes seeds to germinate prematurely?
1. Environmental stress
Vivipary can be caused by environmental stressors, such as water stress (drought or waterlogged conditions) and temperature stress, resulting in changes in hormonal levels.
Vivipary is more likely to occur in fruits that are grown in dry conditions.
Sprouting inside the fruit is an attempt to ensure seed survival for having a higher chance to germinate successfully under a moist environment.
That explains why vivipary is more common in wild plants than in domesticated plants. This is because domesticated plants are typically grown in more favorable conditions, such as in greenhouses or with irrigation.
Vivipary is also more likely to occur in fruits that are grown in warm climates.
A study of papayas in India shows that there are more instances of premature germination of seeds inside fruits during the warmer months compared to the colder months (Saran et al., 2014).
|Incidence of vivipary (%)|
2. Being overripe
When a fruit becomes overripe, the hormones that normally suppress germination is reduced, causing seeds to germinate prematurely.
According to a study by Demir & Ellis (1993), a delay in the harvest of tomato and pepper beyond 80 days could cause overripening of fruits and result in 2 to 5 percent of seeds germinating prematurely.
The reason is that overripe fruits contain a lot of moisture which is optimal for seeds to germinate inside the fruit.
Also, a gene becomes silenced in overripe fruits, causing reduced production of the protective hormone of ABA acid and thus premature sprouting of seeds inside the fruit (Yao et al., 2020).
3. Potassium deficiency
A deficiency in Potassium can also cause seeds to germinate prematurely inside fruits.
One of the important functions of Potassium for plants is the production of abscisic acid (ABA) which can suppress the premature germination of seeds.
A study has shown that low levels of potassium would lead to a reduction of the ABA hormone and premature germination of seeds inside tomatoes (Ochi et al., 2013). And giving plants a fertilizer high in potassium (12.0 mmol/L) could result in a significant reduction in the occurrence of vivipary.
Another study on bell pepper plants also found a higher occurrence of vivipary with plants cultivated in substrates deficient in potassium (3 mmol/L) compared to those cultivated in substrates with higher potassium levels (6 mmol/L) (Marrush et al., 1998).
|Potassium content in the substrate||Fruit with sprouted seeds (vivipary)|
4. Over-fertilization with Nitrogen
Over fertilization of nitrogen can also lead to vivipary.
Nitrates serve to regulate ABA levels in plants. A high nitrate level leads to a reduction of ABA levels, preventing the maintenance of dormancy and stimulating seed germination.
Trees and maize exposed to high levels of Nitrogen in the late stages of fruit development have been found to have a much higher rate of vivipary (Farwell et al., 1991; Wood, 2012).
Another study on melon seeds also shows that plants grown in a high dosage of nitrate nitrogen had a lower ABA content in the juice inside the fruit, resulting in higher occurrence of vivipary (Ochi et al., 2013).
5. Genetic mutation
Vivipary can also happen due to genetic mutations, although it is quite rare.
Some varieties of corn, soybean, and tomatoes are found to be genetically mutated so they are unable to produce ABA. Nearly all their seeds germinate prematurely on the cob or inside the pods. The genetic mutation also affects the growth of viviparous seedlings.
Can seeds sprout inside all kinds of fruits?
Vivipary has been discovered in many commercial cultivars such as tomato, Chinese cabbage, bell pepper, chili pepper, apples, pears, avocado, eggplant, some strains of maize, wheat, barley, rye, coconut, beans, papaya, pecan, some citrus such as grapefruit.
Vivipary has also been discovered in wild plants such as mangroves and several species of cacti.
What prevents seeds from sprouting inside fruit?
Vivipary is naturally suppressed by a hormone called abscisic acid.
Abscisic acid is present in all seed-bearing fruits inhibits the germination urge of the seeds and keeps them dormant. Once the fruit or parent plant dies, or the seeds are released by animal feeding, the hormone’s influence begins to fade, and the seeds begin to travel along a path toward germination as soon as suitable conditions with temperature and moisture arise.
Other methods of suppressing vivipary are found in the way that fruits mature.
Some fruits, like bananas, avocados, and tomatoes, continue to ripen after they are picked. This is because they produce a chemical called ethylene as they ripen preventing the seeds from germinating inside the fruit.
Other fruits, like apples and pears, form a hard shell around their seeds as they mature. This makes it difficult for the seed to break out and sprout inside the fruit.
So, while vivipary can be caused by a number of different things, there are also several ways that plants prevent it from happening.
Can I plant a sprouting fruit?
Not all fruits that sprout seeds will produce viable plants. In fact, most of them won’t.
But if you have a fruit that is sprouting seeds, it is best to plant the entire fruit. This will give the seedlings the best chance of survival.
You can plant the fruit in a pot or in the ground, but make sure to keep it well-watered. The soil should also be loose and well-draining.
Is it safe to eat a sprouting fruit?
It is generally safe to eat sprouting fruits but they spoil very quickly and may have a lower nutrient content and a shorter shelf life.
First, there is nothing toxic in fruits that sprouted prematurely. The seeds sprout because of a low hormonal level of ABA which is not toxic.
However, once the seeds start to germinate, there is a quick drop in nutrients, as they begin to break down carbohydrates, proteins and fats stored in the seeds.
Also, the fruit may spoil easily because the nutrients will break down in simple sugars, amino acids and fatty acids, which spoil easily in storage.
Sprouting fruits generally have a shorter shelf life than non-sprouting fruits because seeds that have germinated are vulnerable to fungal and insect invasion.
If you want to eat a sprouting fruit, make sure to wash the fruit thoroughly and be aware of any signs of rot.
The bottom line
Finding seeds sprouting prematurely inside fruits is relatively uncommon, but it can occur in a variety of plants, including tomatoes, cucumbers, melons, and squash. This can happen under certain conditions, such as when the fruit is damaged, is faced by environmental stressors or when there is a lack of oxygen.
There are several benefits to vivipary for plants. First, it ensures that the seedlings are protected from predators and other environmental threats. Second, it allows the plants to disperse their seeds more widely. And third, it gives the plants a head start on growth by providing them with a ready source of nutrients.
There are some potential drawbacks to vivipary as well. One is that the seedlings may not receive enough oxygen, which can stunt their growth. Another is that the seedlings may compete with each other for resources, which can result in lower survival rates. Finally, vivipary can be disruptive to the plant’s reproductive cycle if it occurs too frequently.
Despite these potential drawbacks, vivipary remains an important part of the plant reproduction cycle. And while it might seem strange to us, it’s actually a perfectly natural phenomenon.
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