help with hormones

[Stone]

I have been using some ''plant starter'' on some seedlings as an experiment.
It contains Indol acetic and Naphthalene acetic acid in low amounts.
It seems to promote root initiation in some plants (but hard to substatiate without a proper trial)
Some seedlings seem to have stalled in their growth. (new leaf stopped growing or smaller). Could this be due to the above hormone causing inhibition of leaf? If so, can I use Gibberellins to counter it? If not, then what should I use and how much?

Thanks

 

[cnycharles]

iba and naa do induce root growth in lots of plants, can't remember if iaa is different form of iba

there is a product used to 'cause' elongation of plants, can't remember as it is late but i'll think of it. commonly used on annuals to give them a jump though too much and they can stretch and/or be brittle

* - it's called fascination

 

[naoki]

Mike, are you sure it is IAA, which is the natural auxins? Most of synthetic auxins are IBA and NAA as Charles said. But this is a minor point because IBA and IAA seems to be similar in function.

The counteracting hormones to auxins is considered to be cytokinins:BAP is frequently available and used. Auxins and cytokinins are naturally used to balance the shoot:root ratio in plants (well it is a bit more complicated than this, but it is good enough for us).

However, I'm not sure if auxins will cause inhibition of leaf. The classic effect of auxins is suppression of lateral bud development (so reduce branching), which is apical dominance. I'm not sure if this applies to sympodial plants, though. But, when people apply cytokinins to Cattleya eyes, it can cause the eyes to wake us. This suggest that auxins are involved in suppression of new growths (lateral buds).

You are talking about leaf creation and expansion of paphs (not creation of new growths), right? Auxins are actually involved near the shoot apical meristem to determine the initiation "pattern" of leaves (phyllotaxis is determined by auxins excreted from shoot apical meristem in several plants). So the gradient of auxins near the shoot apical meristem determines which cells will become leaf in the future. From this, I would speculate that it is unlikely that auxins would reduce the production of leaves.

One thing related to this is that both IAA and IBA are highly sensitive to light. So they may have less effect to shoot where they are exposed to light.

Gibberellic acid (GA) could cause initiation of flowers in some Paphs. It is also involved in elongation of stem (and seed germination), so this might be what you are thinking of, Charles? GA3 is the commonly used gibberelin.

If you still want to try BAP (or GA), I have a couple of papers who used these for orchids, so I can look up the concentration they used.

 

[Ray]

Mike, how much are you using?

I know from first-hand experience that overdosing synthetic auxins (0.1% IBA & 0.05% NAA, applied at about 3ml/L at every watering for a month) will lead to (reversible) flower deformation in phalaenopsis, and I have been given anecdotal evidence that it can "stunt vegetative growth", but I did not see that.

I'm not sure of the mechanism, though, as once the auxins stimulate root tip growth, the roots release cytokinins, which should stimulate shoot growth.


Ray Barkalow
firstrays.com

 

[gonewild]

IAA is a root inducing hormone. It is the best choice when attempting to promote root growth by foliar applications. But it can mess up the plant tissue when in high concentrations.

IBA and NAA do have a negative effect on vegetative growth when they are applied to foliage. The affect on vegetative growth is minimal when they are applied to the stem portion of the plant. The chemicals have the greatest effect on the area of the plant where it is applied to, so applying it to the end of a rootless stem tends to remote rapid root formation from the cells on the stem. Then the chemicals are applied to foliage or upper parts of the stem the same affect happens to the cells on the upper part of the plant, foliage cells start to convert to form roots and vegetative growth is interrupted...... basically it confuses the plant. There has been plenty of research done of the effects.

 

[naoki]

I know from first-hand experience that overdosing synthetic auxins (0.1% IBA & 0.05% NAA, applied at about 3ml/L at every watering for a month) will lead to (reversible) flower deformation in phalaenopsis.

It didn't "click" before, but this makes sense. Flowers are just modified leaves. So the development mechanisms is somewhat similar to leaves. Since auxins are involved in determining which cells become leaf primodia near the apical meristem, it makes sense that the shape of flowers get messed up (the cells which aren't supposed to become petals becomes petals etc).

I couldn't find a simple explanation of phyllotaxis and auxins (most of them are too technical, and I can't understand them), but here is relatively easy ones:

http://mob.wmmrc.nl/auxin/modelling/auxin-morphogenetic-trigger-example-phyllotaxis
http://www.google.com/url?sa=t&rct=...mID4CA&usg=AFQjCNEmhGhfdyD2_5aeNG3Cjr_8EpiU1w

if you are interested in the reason why auxins screw up flower formation.

 

[Stone]

Thanks all for the replies. I don't know much about the subject and it is really only a suspicion that it may be occuring. However it is not on all plants treated only some. I just don't have any other explanation. Plants that where growing well (slowly but well) just decided to stop. Eg a nice little concolor seedling was becoming established after a no grow period. It put out 2 normal leaves and the third just started and stalled completely. Nothing was changed.
This is the product description:http://www.multicrop.com.au/pdfs/Multicrop-Plant-Starter.pdf
Both hormones are auxins. I have used them for about 3 months or so every 3 or 4 weeks at the rate of 2.5 ml/L. I suspect that it may be too often? If you stimulate the plant to initiate roots, do you need to give it a period to go through the root/shoot cycle? I'm used to fast growing plants (shrubs trees etc) where results are very quick to show themselves but maybe I need to give slow growers much more time between treatments?

A quote from Plant Propagation by Hartman and Kester says: ''Application of synthetic auxins at high concentrations can inhibit bud development, sometimes to the point at which no shoot growth will take place even though root formation has been adequate''
Maybe applying too often has the same result?

Naoki, Yes I am talking leaf growth not new side shoots. I have also tried a ''kieki paste'' specially formulated for paphs on an old venustum growth on it's last legs and to my surprize it actually worked! But that's another story.
And yes I'm interested in looking at the BAP paper for the concentrations used! Im very interested if I can kick start these again. It would answer many questions if I can!
I have stopped using the PS for now until I know more.

 

[Stone]

I'm not sure of the mechanism, though, as once the auxins stimulate root tip growth, the roots release cytokinins, which should stimulate shoot growth.

That's what I thought. But if you appy it when the plant is producing cytokinins maybe you are srewing thing right up? So if that is the case then it all comes down to correct timing and so what's that

 

[naoki]

Mike, you are correct; an appropriate cytokinin:auxin ratio is important in making the callus of tissue culture to differentiate correctly. And this same principle applies to the adult (what Ray has mentioned). I have thought that the adjustment of shoot:root ratio is primary coming from suppression or release of the side buds. But I may be wrong about this, and cytokinin may work to increase the overall size (e.g more leaf or larger leaf).

Here is a starting point for the concentration. According to this paper:
Namibar et al. 2012. Effect of 6-Benzylaminopurine on flowering of a Dendrobium orchid. Australian J. of Crop Science 6(2):225-231
they used foliar scary of BAP at 100-300 mg/L (=ppm). 10ml per plant, sprayed in the dusk once per week for the first month, then once every two weeks after that (up to 6 months). They were focused on flowering, and 200ppm seems to be the best.

Last year I tried coconut water (some contains cytokinin) from grocery store for a Catt. eldorado which was declining after importation. It didn't work for this plant.

In most hormones, the response curve has a parabolic shape. So effect may increase till a certain concentration, but if it goes beyond the peak response, the response become weaker and weaker. So getting the appropriate dosage is tricky.

I haven't read the following:
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-3040.1997.d01-72.x/abstract
But the abstract mentions something which you might think interesting. "While urea and NH4+ (vs. NO3) shifted this (cytokinin:auxin) ratio (in the leaf) in favour of cytokinins, thus apparently inhibiting root development in both species." The study isn't applying cytokin. It changed the ratio of N-sources, and looked at the endogenous level of hormones in the leaves of bromeliad. I think these bromeliads are sympodial. So it implies that spraying BAP on your Paphs (sympodial) may work. I think you already use NH4, which could contribute to more shoot (instead of root) growth. But different species seem to have drastically different response to NH4:NO3, so this may not apply to paphs.

 

[Stone]

Mike, you are correct; an appropriate cytokinin:auxin ratio is important in making the callus of tissue culture to differentiate correctly. And this same principle applies to the adult (what Ray has mentioned). I have thought that the adjustment of shoot:root ratio is primary coming from suppression or release of the side buds. But I may be wrong about this, and cytokinin may work to increase the overall size (e.g more leaf or larger leaf).

Here is a starting point for the concentration. According to this paper:
Namibar et al. 2012. Effect of 6-Benzylaminopurine on flowering of a Dendrobium orchid. Australian J. of Crop Science 6(2):225-231
they used foliar scary of BAP at 100-300 mg/L (=ppm). 10ml per plant, sprayed in the dusk once per week for the first month, then once every two weeks after that (up to 6 months). They were focused on flowering, and 200ppm seems to be the best.

Last year I tried coconut water (some contains cytokinin) from grocery store for a Catt. eldorado which was declining after importation. It didn't work for this plant.

In most hormones, the response curve has a parabolic shape. So effect may increase till a certain concentration, but if it goes beyond the peak response, the response become weaker and weaker. So getting the appropriate dosage is tricky.

I haven't read the following:
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-3040.1997.d01-72.x/abstract
But the abstract mentions something which you might think interesting. "While urea and NH4+ (vs. NO3) shifted this (cytokinin:auxin) ratio (in the leaf) in favour of cytokinins, thus apparently inhibiting root development in both species." The study isn't applying cytokin. It changed the ratio of N-sources, and looked at the endogenous level of hormones in the leaves of bromeliad. I think these bromeliads are sympodial. So it implies that spraying BAP on your Paphs (sympodial) may work. I think you already use NH4, which could contribute to more shoot (instead of root) growth. But different species seem to have drastically different response to NH4:NO3, so this may not apply to paphs.

Thanks naoki. I will read that. I was aware that nitrate fed plants generally have a higher root/shoot ratio than ammonium fed and I use nitrate at about 3/4 of the N with the remainder NH4 and urea.