RastaLee
Member
In order for a seed to germinate, many conditions must be met. Firstly a seed must be viable. If a seed is viable it require a suitable environment with proper levels of moisture, suitable temperatures, oxygen, fertile soil, and proper pH levels to name a few. However, as many of us have experienced, some viable (living) seeds will NOT germinate, even when given the perfect conditions. In the field of botany, this phenomenon is known as physiological seed dormancy (will be referred to as PSD from here on out). In plain language, PSD is like a hibernation stage that occurs after seed maturation but before germination.
After the seeds of a mother plant mature, they respond to environmental cues that signal the end of the growing season is near and begin PSD (hibernation). If the seed did not enter this dormancy phase, it would attempt to grow as soon as it reached maturity in the flower of the mother plant. As everyone knows, seeds in the wild do not germinate in the Fall Season because they would soon die during the coming winter months. So it is advantageous for seeds temporarily inhibit the process of germination because it increases their chances of survival and eventual hopes of maturing to breed. Different species of plants use different mechanisms remain in PSD. In botany, PSD can be broken down into two broad categories: Embryo Imposed Dormancy and Seed Coat Imposed Dormancy.
There are many variants to Embryo Imposed dormancy, but the most common and best understood mechanism involves the hormone Abscisic acid (referred to ABA from here on out). The mechanism by which ABA works is pretty complicated without a background in genetics and biology, (inhibits promoter region of genes in plant DNA that would otherwise result in transcription and translation of growth promoting factors as well as enzyme inhibitors that act on the ABA as well as ABAs promoter region) but simply put, ABA is hormone that is produced by plants that potently INHIBITS germination and growth. In a mature plant, ABA is produced in large quantities in response to root disturbance/damage, large and rapid changes in temperature, as well as many other stressful stimuli.(Ever wonder the real mechanism behind transplant shock or why temperature drops greater than 15F-30F stunt plant growth? The answer is ABA)
In contrast to mature plant, in seeds ABA is mainly produced in the cotyledons (1[SUP]st[/SUP] set of immature leaves) of an embryo and is secreted inside the seed at a very slow and constant rate. This will inhibit germination. A sharp decrease in ABA levels disrupts PSD, triggers embryo growth, and thus allows germination. There are many ways by which ABA levels can be decreased. The most understood methods include: Chilling, Phytochrome stimulation, and After-ripening.
Chilling is another way to decreases levels of ABA. Chilling disrupting the enzymes that catalyze the reaction that make ABA. This occurs in nature during the cold temperatures of winter. Seeds that have fallen to the ground are covered by snow or cold soil for 2-4 months and disrupt the production of ABA. This can simulated through a process in botany known as stratification. Seeds are placed in MOISTENED medium or paper towel and kept in a REFRIGERATOR to simulate winter and disrupts the production of ABA. (Do not use the freezer, your run the risk of tissue damage once temperatures fall below 32F. Temperatures between 34F-40F work best. 3-14 days usually works for cannabis, but some seeds may require longer. The longer they are in cold, the more likely levels of ABA will decrease to allow germination).The seeds are then removed from the refrigerator after sufficient time has passed and then planted with optimal conditions.
Phytochrome stimulation is another method of decreasing levels of ABA. Phytocromes are the main light sensing pigments found in plant tissues. In some species of plants, their seeds require light to penetrate through the seed coat, which activate these phytochromes and trigger a complex cascade of events inactivate ABA within the seed. (This is why so many people argue that planted seeds dont need light, while other swear that light produces faster germination. The real truth is, a person that has had seeds that were exposed to a source of light intense enough to have the phytochromes activated already DO NOT need any more light after its planted under the soil because the levels of ABA have been decreased. If the light was not intense enough, then it is plausible that additional intense light even while under a thin layer of soil will activate these phytochromes).
After-ripening happens when a seed dries out (water content below 10%), either from old age or dehydration in the sun. (If a seed company sends you brand new seeds that have not had sufficient time to age or dehydrate, the chances of germination are somewhat decreased without using chilling or phytochrome stimulation. Another false misconception amongst growers, is that if a seed company send you seeds that are old, it decreases the chances of germination. It is true that seeds older than 4-6 years decrease the likelihood of germination, but most of us buy from reputable seed companies that send fresh seeds that are restocked at least once every 3 years. So scientifically speaking, seeds older than 6 months actually have INCREASED chance of germination.) To conclude Embryo Imposed dormancy, one the main factor that controls PSD is ABA! The levels of ABA can be decreased by after-ripening, chilling, or phytochrome stimulation. Now, to discuss the last topic, Seed-Coat Imposed Dormancy.
Seed Coat Imposed Dormancy also occurs by different methods but Ill keep this section short because most people know about this. These methods can broadly be categorized as mechanical constraints or chemical constraints. Examples of mechanical constrains include, thick seed coats or waxy coverings. These constraints prevent the uptake of water into embryo, the expansion of the embryo, the passage of oxygen through the coat to the embryo, or the passage of light to the embryo (phytochrome activation). In nature, seeds are subjected to severe environmental conditions. They roll over rocks, sand, and dirt when the wind blows; travel down small streams and rivers when it rains, and are sometimes eaten by animals, eventually pass throughing their digestive tract. All of these physically abusive possibilities would eventually wear through a seed coat. So we can easily see its advantageous to have a thick seed coat to protect the delicate embryo. In botany, these processes can be mimicked through a process called Scarification. Seeds coats are gently rubbed against an Emory board or fine grit sand paper to thin out a seed coat. This allows the better passage of oxygen and water to the embryo. You must be careful not to damage the embryo!!!
Examples of chemical constraints include, a seed coat that produces ABA (which was explained above), or a seed coat that does not allow the passage of ABA out. This is why soaking seeds in water before germination can be advantageous. The water can soften up a seed coat that too thick, and it can wash away/dilute the perceived concentration of ABA. As ,mentioned before, I purposely didnt go into too much detail here because most people know about soaking seeds in water and scarification. I just included it here to give a scientifically explanation as to exactly HOW these methods work. It still all boils down to ABA.
I brought up these topics before in a previous post with links to books and websites, but I decided to put it all into one place for others to read. If this helps people out, I can go into more details on plant physiology. I have a really extensive background in biology, chemistry, organic chemistry, genetics, physics, botany, pharmacology, medicine and science in general. So if you have questions feel free to ask. Ill probably be posting more info on plant physiology in the future if I find anything useful related to cannabis. Peace and much love!!
RastaLee
After the seeds of a mother plant mature, they respond to environmental cues that signal the end of the growing season is near and begin PSD (hibernation). If the seed did not enter this dormancy phase, it would attempt to grow as soon as it reached maturity in the flower of the mother plant. As everyone knows, seeds in the wild do not germinate in the Fall Season because they would soon die during the coming winter months. So it is advantageous for seeds temporarily inhibit the process of germination because it increases their chances of survival and eventual hopes of maturing to breed. Different species of plants use different mechanisms remain in PSD. In botany, PSD can be broken down into two broad categories: Embryo Imposed Dormancy and Seed Coat Imposed Dormancy.
There are many variants to Embryo Imposed dormancy, but the most common and best understood mechanism involves the hormone Abscisic acid (referred to ABA from here on out). The mechanism by which ABA works is pretty complicated without a background in genetics and biology, (inhibits promoter region of genes in plant DNA that would otherwise result in transcription and translation of growth promoting factors as well as enzyme inhibitors that act on the ABA as well as ABAs promoter region) but simply put, ABA is hormone that is produced by plants that potently INHIBITS germination and growth. In a mature plant, ABA is produced in large quantities in response to root disturbance/damage, large and rapid changes in temperature, as well as many other stressful stimuli.(Ever wonder the real mechanism behind transplant shock or why temperature drops greater than 15F-30F stunt plant growth? The answer is ABA)
In contrast to mature plant, in seeds ABA is mainly produced in the cotyledons (1[SUP]st[/SUP] set of immature leaves) of an embryo and is secreted inside the seed at a very slow and constant rate. This will inhibit germination. A sharp decrease in ABA levels disrupts PSD, triggers embryo growth, and thus allows germination. There are many ways by which ABA levels can be decreased. The most understood methods include: Chilling, Phytochrome stimulation, and After-ripening.
Chilling is another way to decreases levels of ABA. Chilling disrupting the enzymes that catalyze the reaction that make ABA. This occurs in nature during the cold temperatures of winter. Seeds that have fallen to the ground are covered by snow or cold soil for 2-4 months and disrupt the production of ABA. This can simulated through a process in botany known as stratification. Seeds are placed in MOISTENED medium or paper towel and kept in a REFRIGERATOR to simulate winter and disrupts the production of ABA. (Do not use the freezer, your run the risk of tissue damage once temperatures fall below 32F. Temperatures between 34F-40F work best. 3-14 days usually works for cannabis, but some seeds may require longer. The longer they are in cold, the more likely levels of ABA will decrease to allow germination).The seeds are then removed from the refrigerator after sufficient time has passed and then planted with optimal conditions.
Phytochrome stimulation is another method of decreasing levels of ABA. Phytocromes are the main light sensing pigments found in plant tissues. In some species of plants, their seeds require light to penetrate through the seed coat, which activate these phytochromes and trigger a complex cascade of events inactivate ABA within the seed. (This is why so many people argue that planted seeds dont need light, while other swear that light produces faster germination. The real truth is, a person that has had seeds that were exposed to a source of light intense enough to have the phytochromes activated already DO NOT need any more light after its planted under the soil because the levels of ABA have been decreased. If the light was not intense enough, then it is plausible that additional intense light even while under a thin layer of soil will activate these phytochromes).
After-ripening happens when a seed dries out (water content below 10%), either from old age or dehydration in the sun. (If a seed company sends you brand new seeds that have not had sufficient time to age or dehydrate, the chances of germination are somewhat decreased without using chilling or phytochrome stimulation. Another false misconception amongst growers, is that if a seed company send you seeds that are old, it decreases the chances of germination. It is true that seeds older than 4-6 years decrease the likelihood of germination, but most of us buy from reputable seed companies that send fresh seeds that are restocked at least once every 3 years. So scientifically speaking, seeds older than 6 months actually have INCREASED chance of germination.) To conclude Embryo Imposed dormancy, one the main factor that controls PSD is ABA! The levels of ABA can be decreased by after-ripening, chilling, or phytochrome stimulation. Now, to discuss the last topic, Seed-Coat Imposed Dormancy.
Seed Coat Imposed Dormancy also occurs by different methods but Ill keep this section short because most people know about this. These methods can broadly be categorized as mechanical constraints or chemical constraints. Examples of mechanical constrains include, thick seed coats or waxy coverings. These constraints prevent the uptake of water into embryo, the expansion of the embryo, the passage of oxygen through the coat to the embryo, or the passage of light to the embryo (phytochrome activation). In nature, seeds are subjected to severe environmental conditions. They roll over rocks, sand, and dirt when the wind blows; travel down small streams and rivers when it rains, and are sometimes eaten by animals, eventually pass throughing their digestive tract. All of these physically abusive possibilities would eventually wear through a seed coat. So we can easily see its advantageous to have a thick seed coat to protect the delicate embryo. In botany, these processes can be mimicked through a process called Scarification. Seeds coats are gently rubbed against an Emory board or fine grit sand paper to thin out a seed coat. This allows the better passage of oxygen and water to the embryo. You must be careful not to damage the embryo!!!
Examples of chemical constraints include, a seed coat that produces ABA (which was explained above), or a seed coat that does not allow the passage of ABA out. This is why soaking seeds in water before germination can be advantageous. The water can soften up a seed coat that too thick, and it can wash away/dilute the perceived concentration of ABA. As ,mentioned before, I purposely didnt go into too much detail here because most people know about soaking seeds in water and scarification. I just included it here to give a scientifically explanation as to exactly HOW these methods work. It still all boils down to ABA.
I brought up these topics before in a previous post with links to books and websites, but I decided to put it all into one place for others to read. If this helps people out, I can go into more details on plant physiology. I have a really extensive background in biology, chemistry, organic chemistry, genetics, physics, botany, pharmacology, medicine and science in general. So if you have questions feel free to ask. Ill probably be posting more info on plant physiology in the future if I find anything useful related to cannabis. Peace and much love!!
RastaLee
LMAO.
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