I have a question about a polyamine called spermidine. Does anyone knows how many days/weeks/months spermidine is stable in a plant tissue culture that is in a light enviorment with a temperature of 23 degrees Celsius?
Metabolism of spermidine in the cell and its importance
Spermidine is polyamine that could be found in all living creatures. It plays numerous biological roles through interaction with different cellular molecules. Cell growth, development and death are tightly associated with spermidine and two additional polyamines: spermine and putrescine. Their production and metabolic faith are regulated on a DNA level, through controlled expression of enzymes responsible for their synthesis and degradation.
Spermidine is synthesized from putrescine. Reaction is catalyzed by spermidine synthase. Alternatively, S-adenosylmethionine decarboxylase will convert S-adenosyl-L-methionine into S-adenosyl-L-methioninamine that will be converted into spermidine by spermidine synthase. S-methyl-5'-thioadenosine is another product of the aminopropyltransferase reaction and it will be converted into L-methionine.
When it comes to degradation, spermine oxidase can convert spermine into spermidine. Spermidine will be degraded by spermidine N-acetyl transpherase into N-acetylspermidine. N-acetyl spermidine oxidase will convert N-acetylspermidine into putrescine. This degradation pathway is typical for mammalian cells. Rate-limiting step in this degradation is production of N-acetylated derivative. It will be oxidized in the peroxisomes. Formed hydrogen peroxide will be eliminated by peroxisomal catalase. In normal, healthy organism, N-acetylated derivatives will be converted and eliminated from the cell in the form of putrescine. However, that reaction could be skipped. Cancerous tissue could contain large amount of unconverted N-acetyl derivatives implying that altered polyamine metabolism could be tightly associated with carcinogenesis. Various scientists are focused on this discovery and they expect to find some valuable information that could be useful in the future fight against cancer.
Why cells produce spermidine?
Spermidine proved to play important protective role against the environmental stresses. When spermidine synthase gene from Cucurbita ficifolia (type of squash) was introduced into Arabidopsis (experimental plant from the Brassicaceae family) via virus, amount of produced spermidine and effect on overall plant wellbeing were closely examined. Transgenic plant starts to produce and accumulate large amount of spermidine in the leaves when exposed to the negative environmental conditions such as chilling, freezing, salinity, hyperosmosis and drought. It also showed increased tolerability against paraquat toxicity. When transgenic and wild type plant were exposed to low temperature, transgenic plants showed increased expression of several genes for transcription factors associated with protection and responsiveness to stress. Those were DREB and rd29A. This experiment showed that spermidine acts as a stress signaling molecule that accelerates protein machinery responsible for protection against stress.
Other organisms also benefit from spermidine. Most important characteristic of spermidine is its ability to prolong lifespan in yeast and animal species. Spermidine increases autophagy and elimination of old (potentially harmful) organelles and their content from the cell, which is essential for the cell survival. Experiment with Drosophila exposed to oxidative stress revealed spermidine's mechanism of action. Paraquat is a neurotoxin that induces targeted oxidative damage. Flies of both sexes were exposed to paraquat and fed by spermidine afterwards. Survival rate in the spermidine fed group was higher compared to untreated group, but only females from the spermidine group managed to survive. That suggests that spermidine effect is associated with sex-specific paraquat resistance. For some reason, female flies are favored. When smaller dose of paraquat was applied, locomotion of flies was impaired. This time, spermidine in diet improved mobility of both males and females and enhance recovery from paraquat intoxication. Other agent that induces oxidative stress is hydrogen peroxide. Unlike paraquate, it induces general oxidative damage via superoxide anion radicals. When hydrogen peroxide was applied at lower doses, spermidine managed to save the cells and prolong lifespan of the flies. When it was applied in high dose, neither sex nor dose of spermidine couldn't save the flies. Researchers suspected that in both type of experiments, enhanced or disturbed mechanism of autophagy resulted in survival or death of the flies, respectively. Autophagy-related gene 7 knockout flies (atg7–/–) can't express protein essential for autophagy of damaged cellular structures. When atg7–/– flies were exposed to paraquat and tested for survival and locomotion ability, spermidine couldn’t save flies’ life and it couldn't improve their locomotion. When hydrogen peroxide was added, lack of autophagy related gene in combination with high dose of spermidine even accelerated death of male flies. All these experimental facts suggest that spermidine triggers cellular signaling cascade associated with autophagy as most important mechanism for cellular survival during oxidative stress.
Hope this helps.