Howitz and Sinclair state in a brilliant manner: “Our xenohormesis hypothesis proposes that animals and fungi (heterotrophs) have evolved the ability to sense signaling and stress-induced molecules from other species, and that they are under selective pressure to do so. In essence, xenohormesis refers to inter-species hormesis, such that an animal or fungal species uses chemical cues from other species about the status of its environment or food supply to mount a preemptive defense response that increases its chances of survival” Can anybody provide examples in which this hypothesis is unlikely?
I would suggest one: the symbiosis between flavonoid molecules and root nodule bactreia in nitrogen fixation (rhizobium). Thank you...
Dr Joven:
"Can anybody provide examples in which this hypothesis is unlikely? By this specific question are we assuming that their hypothesis is universally likely? At the same token, what are the arguments that their hypothesis is likely, except the ones from their papers? The senior author, with two different coauthors, has embodied the same conjunctures in two journal articles, one in "Cell", the other in "American Journal of Pharmacology and Toxicology", both in n 2008, and parallel manuscripts.
Is executing a preemptive defense response the physiological function of ancient molecules such as flavonoids? Is xenohormesis the teleological function of flavonoids in vascular plants? The number of flavonoid structures known in vascular plants is 8,150 (the number as of the year 2010). “Polyphenols such as resveratrol and quercetin, which are produced by stressed plants, activate sirtuin (silence information regulator) enzymes ...” – Bauer and Sinclair (2008). Really, are these just produced by “stressed” plants? One could say that of resveratrol to some extent; it is a phytoalexin. It is good to learn that onions and apples and tea are products of stress!
Flavonoids may have existed in nature for over one billion years (Swain, 1975) and thus have interacted with evolving organisms over the eons. Clearly, the flavonoids possess some important purposes in nature, having survived in vascular plants throughout evolution (Swain, 1975). The very long association of plant flavonoids with various animal species and other organisms throughout evolution may account for the extraordinaryrange of biochemical and pharmacological activities of these chemicals in mammalian and other biological systems.
Swain T (1975) Evolution of flavonoid compounds, in The Flavonoids (Harborne JB, Mabry TJ and Mabry H eds) pp 109–1129, Chapman and Hall, Ltd., London.
“Resveratrol and curcumin, for example, bear little structural resemblance to one another yet both show potent anti-cancer and anti-inflammatory effects, block angiogenesis…” Howitz and Sinclair. Really? .Little structural resemblance?
“ …xenohormesis refers to inter-species hormesis, such that an animal or fungal species uses chemical cues from other species …”. Cue? Is it only a slight or indirect pointing to a solution then?
The senior author of the paper (see the current question above), Sinclair, has had a major focus on the stilbene, trans- resveratrol, and published its effects on sirtuin (silence information regulator, Sir2) activation. He was the chief executive of the biopharmaceutical company concerned with trans-resveratrol and its congeners (including synthetic molecules). The plasma concentrations of resveratrol in humans are very low, even though the compound seems to be well absorbed. The authors claim that the bioavailability of resveratrol (and flavonoids) can be greatly increased by synergistic and other factors.
The term, “phytoalexins” was defined some years ago as follows: they are low molecular weight, antimicrobial compounds that are both synthesized by and accumulated in plants after exposure to microorganisms.
The flavonoids are biosynthesized from the aromatic amino acids L- phenylalanine and L-tyrosine, together with acetate units (mevalonate pathway of lipid biosynthesis). Flavonoid precursors are at the convergence of two ancient pathways (aromatic amino acids and lipids). The flavonoid biosynthetic pathway (the phenylpropanoid pathway) is part of the aromatic amino acid biosynthetic pathway; precursors of flavonoids molecules condense with acetate units formed from the mevalonate pathway of lipid synthesis.; flavonols (examples comprise quercetin and myricetin) are important intermediates here. The enzymes of the pathway are constitutive, and are conserved for millions of years.
Consider the above in relation to the following:
“Polyphenols such as resveratrol and quercetin, which are produced by stressed plants, activate sirtuin (silence information regulator) enzymes ...” – Bauer and Sinclair (2008).
Just as a small question in Response. Do you think that plants will Change their substances, if humankind gets exstinct? Clear, Nobody will be there to check it.
The Problem with xenohormesis is that you either have to Chose an anthropocentric Point of view (you leave the fields of at least Evolutionary Biology), or you would end up in a conflict (the clues of which species are Chosen and why).
While small children have the right to think that everything happens because of them being there, it might be more advisable for adults to not do so.
Metabolic pathways and enzyme systems catalyzing the generation of polyphenolic flavonoid molecules such as quercetin and luteolin by the two crucial, ancient pathways have been conserved for millions of years, and these molecules are not merely produced in response to stressful factors.
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