I will add to this thread in the coming days, I will post many references and studies for usage of PGRs like brassinosteroids (natural and analogs), triacontanol, auxins, SAR (Systemic Acquired Resistance) inducers, cytokinins (natural and analogs), gibberellins, etc.
I will also post online stores where you can order PGRs and how to calculate the ppm of PGRs for application. When we apply PGRs we are doing so "exogenously" (from the outside); aka "exogenous application".
Two terms that will often be used are "source" and "sink" tissue. Source tissue is where the PGRs are made by the plant, and sink tissue is where the PGRs are translocated to, (sometimes they are not translocated). For example, the rooting hormones IBA and NAA are formed in source tissue (leafs, usually young ones) and trasnlocated to sink tissue (roots, or "basal" end for cuttings without roots).
A.) For now, here is a good head start for people new to the topic:
"Plant hormone receptors: perception is everything"B.) And here is something basic I wrote the other day about my usage of some other PGR's I use:
Brenda Chow and Peter McCourt
Genes & Dev. 2006. vol. 20: pp. 1998-2008
Increases rate of photosynthesis, growth rate and yield. I use it at up to 10 ppm, but after testing lower ppm found lower is better. I am using 0.1 ppm now for testing. Apply every 2 weeks into pre-flower and early budset.
2. Brassinosteroid (as brassinolide or 24-homobrassinolide or 24-epibrassinolide):
Increases rate of photosynthesis, phototropism (light tracking), stress resistance, yield, growth, etc., etc. I found if applying in pre-flower can make plants stretch if over applied; I am testing not applying during pre-flowering. I use it at 0.05 ppm, but 0.01 ppm is also good (lower is better if the same result is found), co-apply with triacontanol.
3. Jasmonates (as methyl ester of jasomic acid [MeJA], aka methyl jasomate, jasomonic acid [JA] or methyl dihydrojasmonate [MDHJ]):
MeJA increases glandular trichome density (over X leaf area) and number (total trichs); as well as being evidenced to increase terpenoid content. Salicylic acid (i.e. Advanced Nutrients 'Scorpion', or the analog aspirin) that is used to induce SAR (Systemic Acquired Resistance), hinders trichome density and number
and has "negative cross-talk" to jasmonates, i.e. it hinders some jasmonate actions.
There is some evidence that brassinosteroids and jasmonic acid also have negative cross-talk, thus I apply methyl jasmonic acid alone (i.e., methyl easter of jasomic acid), and only in pre-flowering. I apply it as 100 ppm, but 50 ppm is also good and I am testing at lower ppm soon, e.g., 10 ppm and 25 ppm (lower is better if the same result is found).
4. Gibberellic acid (as GA3):
It makes plants stretch/grow, but that's not why I use it, when co-applied with jasmonates they work in synergy to increase trich density and number. However, this can really make plants stretch so use with caution. This can really make plants stretch so I won't suggest ppm right now, I need to do more testing with methyl jasmonates during pre-flowing and flowering...