I have compared clones raised from both coconut water and synthetic PGRs. When I checked the fidelity of the hardened plants where I used coconut water as the additive it gave a lesser degree of variability than the clones raised from synthetic PGR mediated micro propagated plants. What can be the possible reason?
By "lesser dsegree of variability" what do you mean - physical changes in the growth and development of the hardened off seedlings/regenerants or have you a measure of the genetic variation within the clones?
We are actively studying the casues of somatic variation in grapevine and in particular the role that transposable elements play in altering the genome both genetically (through the introduction of new transposon insertions) and epigenetically (through alteration in the silencing state of the existing transposons and transcriptional acitvation of the existing elements in response to biotic and abiotic stress).
Like many others we have found that a range of biotic and abiotic stressors are capable of activating TEs. However the level of activation and those elements that area able to be activated are dependant on the tissue and developmental stage of the tissue you are using. In our case we have found that treatment of grapevine somatic embryos with a range of stressors activates a number of TEs.
Part of what is happening here is that the cis-regulatory elements that drive the transcriptional activity of the TEs often contain a range of stress-sensitive core sequences. The nature of the stress response pathways is that the plants response to these stressors is communicated through alteralions in PGRs. Consequently TE activation and in particular in embryonic cell culutres (where often the epigenetic landscape is much different to other tissues and often lessened leading to the potential activation of TEs) can be stimullated by application of PGRs that mimick a plant stress response. High levels of PGRs required to stimulate organogeneisis may also lead to a tissue stress.....however the process of tissue organisation as part of organogenesis may also allow stimulation of TE activity.
The consequences of increased TE activity may be the stimulation of new TE insertions and resultant mutagenic activity. Additionally existing elements and in particular the retrotransposable element classes will not only be stimulated to produce a transcript of the TE but can often also transcribe the flanking DNA. This is likely in a nuber of cases to either activate genes flanking the TE or attract the attention of the silencing machinery leading to either post transcriptional silencing of the RNA or methylation of both the TE and flanking DNA. This is in essence a epigenetic response and we hypothesise may lead to a number of new phenotypes in regenerated plants....some may be transient and yet others may be more permenent depending on the nature of the silencing that is attracted to particular TE loci and the DNA flanking their insertion sites.
Getting back to your question about what may be driving the differential response in terms of variability....potentially the synthetic PGRs you apply are moreeffective at stimulating a stress-like response than the PGRs within the coconut extracts - As we see that different treatments over different time courses etc can have quite marked affects on TE activity. Generally we see greater physical variation in plants raised from SE cultures treated to hyperstimulate TE activity as compared to those treatments that show lesser activation of TEs.
Hope this helps.....it is a facinating area of science
In my previous experience in plant genetic resources conservation, our lab minimize the number of subcultures to control somatic variations in the micropropagated germplasm materials. In your situation, I am not sure if the variation you observed is during the first cycle of culture. Coconut water contains several phytohormones such as auxins and cytokinins. So it would be difficult to pinpoint among these components of coconut water contributed to the fidelity of your genetic material.
Natural cytokinins and other plant growth phytohormones found in the green coconut water are general better for plant tissue culture and giving rise to lesser incidences of of somaclonal variation. We think that it is the type of plant growth phytohormone that changes alot of stuff:
https://www.researchgate.net/publication/40768354_The_chemical_composition_and_biological_properties_of_coconut_%28Cocos_nucifera_L.%29_water?ev=prf_pub
Article The Chemical Composition and Biological Properties of Coconu...
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