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Polyamines have been linked with many diverse functions. In order to understand the exact functions of polyamine, we have to go back and try to determine the initial function of polyamines. After that we can proceed to the other functions that polyamines obtained during evolution. The previous theory assumes that buffering and balancing the ion balance in the plant cell is the basic function of the polyamines. This is the starting point of the theory that in the end will give a possible answer on how a plant can adjust to a changing environment during its growth cycle, how and why polyamine induce flowering and how dormancy works. According to the theory presented, this is only possible if a plant has feelings. But what are feelings? What are the prerequisites for having feelings? Does the plant poses the mechanism to fulfil these prerequisites? And if the plant has feelings, is a plant an optimist or a pessimist? Can a plant forgive and forget? Should we pay attention to the feelings of plants, or do we already pay attention to the feelings of plants without knowing it? Can and do we play with the feelings of plants? Polyamines play a key role in a plants life and the importance of this is underestimated. The theory presented here tries to explains the function of polyamines by looking at the origin of the different functions. The ideas are based on facts reported in literature and developed by using the logic of evolution.

Before you read this hypothesis/theory, you have to read the two other theories on which it is build upon, namely “Plant hormones: ideal metabolic marker molecules” and “Plant hormones: functions revised”. Both can be found on www.plantevolution.info.

Before we can examine if a plant has feelings, we have to define feelings. What are feelings? To feel means to notice a difference, signal this difference and react upon this difference. The first theory “plant hormones: ideal metabolic marker molecules” linked a change in the metabolism of the plant with the production of a plant hormone. The capability to react upon change by the production of plant hormones is however not enough. To feel also assumes that a distinction can be made between good and bad. The different plant hormones can be divided in two groups based upon the origin of the process that initiated the production of these plant hormones and the response these plant hormones evoke in the plant. There is the group of positive growth regulators, namely auxin, cytokinin, gibberellins and brasinosteroids. The group of negative growth regulators, linked to inhibition of the growth, comprises absisic acid, ethylene, jasmonic acid, salicylic acid and polyamines. In relation to the positive growth regulators, a distinction has to be made between the regulators of normal growth of the plant and regulators that signal extra growth potential. How good a plant is growing and feeling is reflected the best by the gibberellins. The group of negative growth regulators comprises mostly signals that only reflect one type of stress. Only polyamines bypass this problem as they change under every type of stress a plant can experience. The polyamine content of the plant therefore gives the best estimate of the negative status of the plant.

During the course of evolution, a plant growth regulator became plant grow regulator because the plant started to react upon a rice of the concentration of that particular molecule. This means that during evolution the plant learned how to react on a signal at the same time as the signal molecule became a signal. The birth of a new plant hormone always started with a new gene that coded for a receptor that reacted on the signal molecule and invoke a response in de plant cells. A new gene also means that the reaction of the plant on a change in the concentration of the new plant hormone is inscribed in the DNA. From now on the plant “knows” how to react. The plant obtained many other new genes during the course of evolution when new signals were adopted or new secondary functions were connected to existing signal molecules. The modern plant has all the reactions upon signal molecules inscribed in its genes. This knowledge allows the plant to react to the ever changing environment in which the plant lives.

Coordinated Until know the previous theories assumed a direct link between the environment and the plant. A direct action-reaction mechanism without consideration of the past. This is however not what can be observed in nature. The reaction of the plant will always depend on the history of that plant. This observation assumes that plants have a memory. Having a memory is also one of the prerequisites for having feelings. The question now is: how does the memory of plants work? If we assume that gibberellins represent good feelings and polyamine bad feelings, than the amount of these molecules reflects the overall status of the plant. However, when a plant cell divides, the gibberellins and polyamines are not duplicated. Therefore, cell division always equals a reduction of the concentration of both compounds. That is, if no new gibberellins or polyamine are produced which again lead to an increase of the concentration of these compounds. The last is only possible if the plant again experiences something good or bad. The amount of gibberellins and polyamines can therefore not serve for the memory of the plant. Similar reasoning can be done for proteins in the cells. Moreover, they have a fast turnover rate and are therefore a less suitable candidate for storing memory. Memory must be something which can be inherited and does not disappear during cell growth or cell multiplication. The inheritable information of a plant lays in the genetic information coded in its DNA. Although DNA is the ideal candidate to store and transfer information, the genetic code normally does not change that easily. During evolution, the plant found/developed a solution that bypasses the problem of an unchangeable genetic code. This solution is inheritable DNA-methylation. DNA-methylation does not alter the genetic code, but may influence the transcription of the genetic code. By doing so, the gene expression can be altered, meaning that the plant will behave differently after the DNA has been methylated. It can be assumed that this mechanism of influencing gene expression was already present before the evolutionary selection process of plant memory began. The genesis of plant memory only asked for one extra enzyme. Namely an enzyme that copied the methylation pattern of the nucleic acids of genetic code during DNA replication. This elegant solution does not only make the information heritable, but also links the storage of memory directly to the expression of the genes.

The next question is: when does methylation take place? To answer this question, we have to know if the nature of plants is optimistic or pessimistic. When looking at modern plants, it is clear that all plants start optimistic. Seedlings are fast growing and keep on being so until stress occurs. This is logical as the plant must compete with other seedlings. A cautious growing seedling will lose the competition for light and will therefore not survive. When looking at the shoot formation of trees in spring, a similar tendency is observed. The leafs on the bottom of the shoot, disregarding the rosette leaves, are always bigger then the leaves on the top of the shoot. It is however not so that the biggest leaf is the first leaf of the shoot. Often the biggest leaves are situated just after the first leaves. The reason why these leaves are bigger must be sought in the better growth conditions that occurred during the development of these leaves. More optimal growth conditions equal the formation of gibberellins that enhance the growth. From the observations of the shoot leaves it is however clear that the enhanced growth only lasts as long the optimal growth conditions last. Once stress occurs during the growth of the shoot, the size of the leaves decreases and leaves will never grow as big during that growth season as the first leaves of the shoot. This is excluding regrowth which sometimes occurs. (The mechanism behind regrowth will be discussed later in this article.) The same thing accounts for seedlings. Once experiencing stress, the plant will never become as big as a plant that never experienced stress during its lifetime. When overlooking the growth of the shoot and the seedling, it can be concluded that plants do only keep remembering stress situation. The influence of optimal growing environmental conditions is very limited in time. In the beginning of this article, it was postulated that sensing bad things that happened to the plant are signalled the best by polyamines. Polyamines are produced from arginine. The first polyamine that is formed is putrescine. Putrescine is know to induce DNA methylation. Putrescine is therefore the compound that induces memory in the plant. Until now, gibberelins and brassenosteroids have not been linked in the same way with DNA methylation. Once the concentration of these hormones goes down, also the positive effect on the growth will decrease. The concentration of planthormones, gibberellins, brassenosteroids can be looked at short term memory of good things that happened to the plants. The concentration of the polyamines can be looked at in a similar way, namely short term memory in this case from bad things that occurred recently. On the long term, only through DNA methylation a plant can remember its past. Putrescine is the compound that initiates DNA methylation and only situation that coincided a rise in putrescine will therefore be remembered by the plant. This means a plant only keeps track of bad things that happened to him.

The question when to flower and the relation with plant hormones, more precisely polyamines, was discussed in the proceeding theory “Building a plant: plant hormone functions revised” (www.plantevolution.be). In this theory, the question when to reproduce was linked to the occurrence of stress, signalled by polyamines. A plant needs to estimate the necessity to reproduce. This means balancing the competitive advantage of keep on growing versus the choice to replicate to assure survival of the plant species on the long term. In the previous theory it was already mentioned that this choice can not be based upon one type of stress. This is the reason why polyamines, which rise under every type of stress, are the best metabolic marker for measuring overall stress. The plant will however not flower every time it experiences stress. A certain stress threshold must be reached before it is worthwhile to reproduce. There are different types of polyamines present in a cell. Not all of these polyamines are produced in the same quantities when stress occurs. The first polyamine that is produced from argenine is putrescine. Two other important polyamines in plants are spermidine and spermine. Spermidine is derived from putrescine and spermine from spermidine. A rise of the putrescine concentration is the first reaction of the plant cell upon stress. If the stress is more severe or it stays for a longer period, also the concentration of the two other important polyamines will rise. Flowering based upon putrescine will lead to earlier flowering then necessary, as not all stress is live threatening. A rise in the concentration of spermidine or spermine is therefore a better candidate for signalling the time to reproduce. Research has shown that spermidine is linked to the induction of flowering. The logic used above explains why spermidine was the best molecule to signal the time to flower. This is however not the complete story of flowering. The concentration of polyamine in a plant cell only gives the status of the plant cell on that time point and the near past. A decision when to flower only based on a rise of the spermidine concentration is still a bad decision.

In the previous section, the polyamine putrescine was linked to the memory of the plant. If we assume that the role of putrescine in plant memory was already established before spermidine started to signal for flowering, then it is almost certain that plant memory also plays a role in flowering. Putrescine induces methylation of DNA. A plant will react differently after DNA methylation. DNA methylation will alter gene expression. If a gene would only respond upon spermidine if this gene is methylated, then the signal for flowering would comprise also the memory of the plant. In this case the decision to flower is not only based on the current status of plant, but also takes into account the history of the plant. The selection of such a signal clearly has evolutionary advantages. This type of signalling is also possible if the role of putresine in plant memory was established after the role of spermidine in flowering. In this case however the DNA composition had to evolve in such a way that DNA methylation takes place in those genes responsible for the induction of flowering. The end result is the same and does not depend on the question which function was linked first to the polyamines. Spermidine indicates severe stress and induces flowering only when the plant already experienced stress before that time point. A certain amount of stress must have occurred that resulted in an increase of putrescine and concordantly DNA methylation. Spermidine will only induce flowering when certain genes are methylated, or when certain genes reached a certain methylation level.

To my opinion, the mechanism explained above is the basic signalling active in all flowering plants. Later on during evolution, the flowering signalling got more refined and diverse. Adjustments were made which were beneficial to the plants in question. For example, some plants linked flowering also to the length of the day and/or night time because this had evolutionairy advantages for these plants. The theory presented above furthermore explains why flowering does not only depend on the presence of a plant hormone that signals for necessity to flower. According to the theory presented here, the plant hormone that induces flowering does exist, but it will only induce flowering when other factors/requirements are fulfilled. Decision making on when to flower is a based upon a signalling mechanism that gives the best estimate of the status of the plant, taking into account the whole live cycle of the plant.

Evolution Until know, we have assumed that at a certain time the plant has to make a choice between vegetative growth and reproduction. This simple view does account for non perennial plants. The situation becomes more complex in perennial plants. A perennial plant needs to keep on growing in order to compete. However, according to the theory presented above, the DNA of the plant becomes methylated which slows down growth, and later the plant stops growing when flowering is induced. This is however not the case in perennial plants. They will stop growing for a while, for example during winter time, but after that start to regrowth. Following the logic of the theory above, this is only possible when the DNA is demethylated. Only then the plant can regrow. In non-perennial plants, demethylation normally takes place during the production of gametophytes. During meiosis, DNA demethylation takes place, demethylating most of the plants DNA. (The part of the DNA that is not demethylated, equals the memory that will be inherited by the following generation. More information on this topic can be found when looking for info on epigenetics in plants) Perenial plants do not undergo meiosis before regrowth occurs. In order to evolve from a non-perennial to a perennial it was therefore necessary that evolution selected a signal that could be linked with demethylation. This signal is spermine. Spermine is produced from spermidine. It will only be found in larger quantities when severe stress occurs. The question now is: Why was spermine selected during the course of evolution as the ideal signal for inducing demethylation? For this we have to go back to the time point when the plant decided to flower. The decision to flower was made because flowering was a better strategy to survive than keep on growing. This decision is based upon spermidine and the degree of DNA methylation. When flower induction starts, vegetative growth stops. Normally the plant will die after flowering due to unfavourable growth conditions after flowering. It is however possible that in some cases the plant kept on living (not growing!!) and survived the bad growth conditions that took place. If this plant would find a solution to restart growing, then it would have evolutionary benefits as it is already bigger then its competitors. In order to guarantee the success of this new regrowth strategy, the plant had need of a signal that could trigger the regrowth at the right time. Similar to the evolutionary origin of the other plant hormones, the best metabolic marker for signalling regrowth will be selected. The best metabolic marker for triggering regrowth will be the molecule that gives the best estimate of the waiting period proceeding regrowth. This waiting period is characterised by non optimal growing conditions. This can be rightfully assumed because the decision to flower was made upon an increase of spermidine and high levels of DNA methylation, which reflected the occurrence of severe stress and the necessity to reproduce. The selection process that takes place selecting the signal molecule for measuring the waiting period must be a molecule that can signal both the length of the waiting period as well as the end of severe stress occurring during this waiting period. Only in that case regrowth will be a successful strategy. Again there is the need to measure the status of the plant. As mentioned before, the molecules that give the best estimates of the status of the cells are the polyamines. The next question will be: which of polyamines is the best candidate for signalling the possibility for regrowth? Putrescine is already linked to the promotion of DNA methylation. This makes it an unlikely candidate for becoming the signal molecule for regrowth. The signal molecule for regrowth will be linked with DNA demethylation. Two other candidates are spermidine and spermine. The stress that the plant experiences during the waiting period is more severe or more prolonged then the stress the plant experienced before flowering. If this would not be the case, then this would mean that the plant started to flower to early because there was still time/opportunity for vegetative growth. More severe stress means that not only the levels of putrescine and spermidine will rise, but also a large increase of spermine is possible. Spermine is the better marker molecule for severe stress. This makes it also the best molecule to play a role in the mechanism initiating regrowth. Linking DNA demethylation to an increase of spermine is a mechanism that links the measurement of the length of the stress period to the reset of the plants memory. After the memory of the plant has been reset, regrowth can occur. Because a rise of spermine never occurs without a rise of putrescine, one can assume that at the same time point when DNA demethylation occurs, also DNA methylation takes place. Actual DNA demethylation can only occur if the DNA demethylation is more active then DNA methylation. A second possibility is that spermine or the DNA demethylation proces inhibits DNA methylation. The competition between DNA methylation and demethylation has an advantage which benefited spermine to become the signal molecule resetting the plants memory. This advantage is that only at the end of the stress period DNA demethylation can take the upper hand from DNA methylation. Total DNA demethylation is only possible if also DNA methylation stops. This makes that the plant only has totally unmethylated DNA at the end of the stress period. All this made spermine the best possible candidate to reset the plants memory.

There is one aspect of polyamines that has not been adressed until now in this article, namely: polyamine also directly interact with DNA. It is almost certain that this feature of polyamine plays a role in the influence that the polyamines have on the gene expression. Putrescine, spermidine and spermine interact differently with DNA. This difference is exploited during the course of evolution, influencing the composition of DNA. A difference in composition of nucleic acids in DNA can result in a difference in gene expression when different polyamines are present. All this does not change anything of the hypothesis presented above.

In the paragraphs above, a theory was presented that showed that plant know, sense and remember good and bad. This means that the plant fulfils all the prerequisites needed to feel. If this is true, we should be able to evaluate the plants nature. Evaluating the nature of the plant equals evaluating the gibberellines and polyamine production during the plants live time. These markers give a good indication on the good and the bad times of the plant. Furthermore, DNA methylation must be looked upon, reflecting the memory of the plant. Only then, the reaction and behaviour of the plant can be fully understood.

The plant starts with unmethylated DNA, this means a blanc memory. This makes that it has a very competitive nature at the beginning. The plants compete for light, water and nutrition. The climatic conditions will determine how competitive the plant will be and if it stays competitive. Under optimal growth conditions, the competitive nature of the plant will be temporary enhanced. The concentration of the gibberellins rises under these conditions, initiating extra growth potential. This extra growth potential will however only last as long as the concentration of gibberellins are high. This is the first fact that proves that the plant is not only competitive but also cautious. The cautious nature of the plant is even more proven by the fact that plants remember only stress situations. The cautiousness due to stress will begin when the putrescine concentration rises for the first time and DNA methylation is induced by the elevated putrescine concentration. DNA methylation influences gene expression resulting in a plant that will never be as competitive as it was in the beginning. It keeps remembering that stress occurred. Being cautious means that he knows that growing/competing without limits is not without danger. If a plant would be incautious, then this could endanger the survival of the species on the long term. Growing without being able to produce seeds for the next generation due to a lack of energy is what the plant wants to prevent by inducing memory.

The hypothesis does not only enable a psychic analysis of the plant, but also assumes that one is able to measure the actual 'mental' status of the plant. If one measures polyamine and gibberelline concentration and the level of DNA methylation, then a good estimate can be made not only of the condition of the plant but also of how a plant will react upon certain environmental changes. For example, a plant in cautious state due to methylated DNA will react differently then a competitive plant with only unmethylated DNA. The same accounts for plants with a high and low gibberellin or polyamine concentration.

Vernalization is the acquisition of a plant's ability to flower or germinate in the spring by exposure to the prolonged cold of winter. Cold temperatures result in the disfunctioning of the plant membranes. When temperatures drop, the fluidity of the membrane goes down. This increases the chance of water loss. Membrane leakage is much more pronounced under very low temperatures then it is under high temperatures that induce drought stress. This means that also under low temperatures the concentration of polyamines will rise. This rise will be more pronounced and prolonged then it is in the case of drought stress during summer. The concentration of spermine will therefore be the highest during winter and/or the spermine concentration will last longer at a high concentration. Vernalization is just another case of dormancy and can be fully explained by the theory presented above.

During the growth season, regrowth can occur. Regrowth is when the plant stopped to grow during the season due to bad environmental conditions, but then resumed growing later on. When regrowth occurs, the plant does not only start to regrow but also forms again bigger leaves then it did before it stopped growing. The new leaves are however not as big as the once produced at the beginning of the growth season. Regrowth occurs when optimal growth conditions, occur after a period of stress. Due to the stress the concentration of putrescine increased, DNA got methylated and the plant became cautious and decided to stop growing. If the amount of stress experienced by the plant was very high, also the concentration of spermine rose. If directly after this stress period rain falls and the temperature and light becomes again optimal to grow, regrowth is possible. Optimal growth condition will lower stress and therefore also the production and concentration of polyamines. At that timepoint, regrowht can occur because the DNA demethylation activity in the cell induced by spermine can possibly sometimes become higher then the activity of DNA methylation induced by putrescine. During a normal growth season, regrowth would normally not occur because normally after a stress period that induced the growth stop, the growth conditions are far from optimal. This means that normally there is not a quick decrease in the polyamine production of the polyamines after the grow stop. The conditions that induce regrowth are however different and lead to a drastic decrease of the production of polyamines. This allows DNA demethylation induced by spermine to take the upper hand over DNA methylation. Regrowth is an exceptional case of the breaking of dormancy that also can be explained by the theory presented above.

Second flowering that can occur on trees is a special case of regrowth. If the shoot growth stopped with a flower bud, regrowth will appear as a flower. All that accounts for regrowth, also accounts for second flowering.

Some of the ideas in this theory are new, others are not. Good ideas were taken over, other ideas were adjusted and new ideas were added. The originality of the theory lays in the use of evolutionary logic to explain the origin of the functions that polyamines required in the plant. Furthermore, the importance of the polyamines was highly underestimated in proceeding theories on the function of polyamines. The central role in plant memory, flowering, dormancy and regrowth is given in this theory to the polyamines. The assumption that polyamines signalling forms the basis of all these processes and only later other factors started to influence these processes, is a new viewpoint. According to me, it is also the first time that an explanation for dormancy is given based on the interaction between putrescine and spermine. The effect of putrescine and spermine on DNA methylation was already described, but never was the link made that the interaction between those compounds could fulfil and explain the release from dormancy. Not new, although not excepted by all, is the assumption that there is no difference in the mechanism between different types of dormancy. With the theory presented above, new arguments are given that could prove the similarity between the different types of dormancy.

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