Dear Ricardo, i would like to present you this paper published in one of the most important journals in Brazil. It has something about what you ar asking, but in field conditions. We've studied the behavior of Brachiaria decumbens (a forage grass) established in a silvopastoral system, i.e, under different light conditions. I hope this helps you.

http://agris.fao.org/agris-search/search/display.do?f=2011/XS/XS1021.xml;XS2010T00081 or http://www.scielo.br/pdf/sa/v67n5/v67n5a14.pdf (here you can get the pdf.) This paper is also in my publications (my home)

Look for hormones effects in plant tissue culture.

The ratio of auxins to cytokinins has a great impact in the ratio of roots/shoots. I don't know which concentrations are you using for your micropropagation, you can check that. If you don't want the results you are getting, perhaps adjust the levels of growth regulators

Sugars and hormones in the rooting medium might promote root over shoot growth.

Root to shoot ratio in natural conditions depends upon photosynthate avialable, however in culture it is very much depends upon concentration of plant growth hormone and ration of CK to Auxin used in the experiment.

I would consider to measure waterstress first. Reason is that roots and shoots at large react opposite to water stress. roots grow more (search a larger volume for water), and shoots grow less (avoid wilting in the abscence of sufficient water supply). Experimentally, this can be tested by increasing the negative water potential (eg. increasing PEG 6000 concentration applied to filter paper). in general the cell need to increase its turgor pressure to enable a volume expansion step and hence elongation of the cells. Roots can actively accumulate ions parallel with the radial water uptake and hereby maintain an osmotic gradient for water uptake. Shoot growth is dependent on the water provided by the roots to increase its turgor pressure and promote growth.

I presume the enhanced root growth in culture is mainly due to concentration of auxin and sugar- the role of water stress on the root growth has to be studied to confirm

I think that balance of the endogenous hormones is main cause for this reason

My answer is based on theory and not experiment. Roots need carbohydrates usually supplied by shoots to grow in an autotrophic situation. In heterotrophic situation as in vitro culture, roots could gain carbohydrates easily from medium and grow more than shoots that are now dependent on them. Reducing the carbon source concentration may help in addition to full light conditions to help them go towards becoming autotrophic and more shoot growth. using a cytokinin in medium may be beneficial as well because it could arrest root growth while enhance shoot growth when transported to shoots by roots, just a guess

I think the Roots need carbohydrates usually supplied by shoots to grow in an autotrophic situation on xilem. as in vitro culture, roots could gain carbohydrates easily from medium and grow more than shoots that are now dependent on them. Reducing the carbon source concentration may help in addition to full light conditions to help them go towards becoming autotrophic and more shoot growth. using a cytokinin in medium may be beneficial as well because it could arrest root growth while enhance shoot growth when transported to shoots by roots.

I also think it is to do with the plant hormones, you can see related articles, there has been examples where people have cultured shoot tips in vitro and have observed growth of roots without even adding any growth hormone in the basic growth media but required to add a IAA to initiate shoot. So to have more shoot density you need more IAA.

Normally in tissue culture we prefer to let the shoot proliferate and the induce them to produce roots. But it depends, in some instances like banana both can take place together. C source come from the sugar added in the media normally the basal MS

I am not a tissue culturist. Except small practicality course done. There could be ecology that is also playing a role. A adverse-like to overcome of something that is beyond use. A kind of limiting factors to be created for optimum growth of shoot/root.

Can we consider of that particular plants how behave in natural soil conditions can be kept as a thumb rule.

I feel anything excess/lack of it be it hormone/nutrients of one or the other creates excess root growth in anticipation of exudations/utilizations as biomass or in searc of.

All depends on balance of hormones in the medium of cultivation. You can look at it in classical works of Murasiges and Skuug. When there is a lot of auxines in the environment many roots. When there is a lot of cytokinin much shoots. Hydrocarbons play a significant role in regulation of a physiological condition of plants. It is known that some oligosaccharides can influence on balance of phytohormones by means of strengthening of synthesis of these or those hormones. Respectively you also receive, again depending on concentration of sugars authentically high root or shoot regeneration.

That depend on - kind of growth hormones - light distribution on root and shoot zoon in incubator - carbon source and its concentrate - plant you are wok on

and don't forget also light source. Different types of light source can affect plant growth, particularly shoot growth (or aerial parts).

The group at INRA in Lusignan used to work a lot with tall fescue when I did an internship there in the late 90s (see link). Additionally you might find some information with Prof Schnyder and Prof Schmidhalter from Technische Universität München. What plant are you working on? To my knowledge in a plant systemroot growth generally preceeds shoot growth. The partitioning (blalance) is regulated by hormones which can be induced by nutrient availability, especially Nitrogen.

http://www.poitou-charentes.inra.fr/poitoucharentes/ses_unites/prairies_et_plantes_fourrageres/ecophysiologie_des_plantes_fourrageres/publications

The culture is fully depends on the medium i.e. glucose concentration around the extracellular medium, growth harmones, AA and different types of light

I also endorse M. Hess. Few points also to be taken into account while concluding the root behaviuor in culture medium. In natural condition root comes first, i.e. potential of a cell. This initiation is considered to be due to auxins, thereafter cytokinin s comes in for further differentiation leads to shoot formation( cocktail of hormones may be, as no one has gauged other hormone produced once cell differentiation & growth begins), essentially required for inclusive growth of normal plant. Of course, at beginning of the process root is a great sink , nutrient supplied from the medium used , hence fast and more growth, but after attaining certain stage , no root growth . rather shoot growth will take over depending on genus/species. Now, why root growth is first & more is because plant tend to establish it. and accordingly partitioning of dry matter occur .

The responses being received by response regulator will also play role in the varied responses, i.e root/ shoot growth

Thanks all of you for the inputs. I´ll try to make a resume and answer to some questions. I´m working with walnut, a hybrid for wood production. Of course, hormonal balance play a fundamental role. I had found some reprints that make some ligth on. Under normal conditions there is a close relationship between shoot and root growth, once root needs glucose and hormones made up in the top of plants for growth as well as shoot needs to its normal development minerals intake by roots . In vitro, carbon source normally has to be supplied in the culture medium, hence, it´s expected that in some momment microcuttings have to compete for it; before this point if there is suitable conditions for rooting, microshoots form roots, but if it´s not they feel free to enhance to size of shoots.

In my experience the carbon source is important to develop root from shoots..all plants are not responsible to promote the root from auxin. The carbon source like sucrose, glucose, dextrose, maltose concentration are induce the root production depends on the plant growth and characterization. The auxin with carbon source can induce the callus on shoot, so you can promote the root induction by carbon sources without supplementation of plant growth regulators.

I haven't read the comments. perhaps some one has already mentioned that. "Root - shoot ratio" is an important concept in tree physiology and forestry. There are couple of good articles on internet regarding this topic.

Can you sent me the title of papers? Thanks

I am not expert in this topic but if you search "Root shoot ratio" in a scientific article database, you will surely come across dozens of articles. for example: "Effects of mineral nutrient deficiencies on leaf development, visual symptoms and shoot–root ratio of Spathiphyllum"

Rice in general is transplanted in puddle soil. It helps in mainly two ways. Root growth restricted, results more biomass accumulation in shoot. Under puddle condition concentration of nutrients is greater in a small area. Optimum root biomass utilizes the Nutrient in an efficient manner. Both plant and man invest on root according to the need.

perhaps some one has already mentioned that. "Root - shoot ratio" is an important concept in tree physiology and forestry.

Roots get water and mineral from soil, this matter very imporant for fotosynthesis...

So roots primarly for biochemystry at plant

Dear Ricardo, i would like to present you this paper published in one of the most important journals in Brazil. It has something about what you ar asking, but in field conditions. We've studied the behavior of Brachiaria decumbens (a forage grass) established in a silvopastoral system, i.e, under different light conditions. I hope this helps you.

http://agris.fao.org/agris-search/search/display.do?f=2011/XS/XS1021.xml;XS2010T00081 or http://www.scielo.br/pdf/sa/v67n5/v67n5a14.pdf (here you can get the pdf.) This paper is also in my publications (my home)

Thanks for the information Marcelo

i just read Rodney Kahn's discussion on walnut and it reminded me that as an undergraduate I did some work on a black walnut range-wide provenance test. if I remember right, black walnut was unusual in that release from winter dormancy (bud break) was due to changes in photoperiod instead of an accumulation in chilling hours that is almost ubiquitous in other tree species that experience true winter dormancy, as opposed to simple quiescence. In many species root growth and above-ground growth are episodic. For instance, in trees a spurt in root growth typically preceedes bud break in the spring and roots continue growing longer into the autumn than above-ground growth. Also, with respect to the root:shoot ratio, it is typically not isometric. That is, it changes as plants get bigger. Variation in root shoot balance is best assessed by comparing plants of simliar size using allometric analysis.

Rodney and Kurt, first, I would like to thanks your comments. I don´t have any feedback about the behaviour of my vitroplants under greenhouse conditions, yet: right now, after read your comments, I'm feeling quiet. My walnuts growth really fast during acclimation, mainly root system, under long days (not less than 16 h light) and temperatures ranging from 16 (better above 20) to 32º C: from the beginning of acclimation to the moment in which roots fulfil a pot with 1 L of volume elapse only 9 weeks (once our protocol was defined to acclimate rooted microshoots they are potted first during 6 weeks in a 200 cm3 pot of capacity). In my experience when vitroplants have a weak root system they have difficulties to face the winter, even under greenhouse conditions; anyway when spring begin mostly of them are able to resume the growth: I´ll keep in mind Promalin for the next season. In all cases, I’m having a nice experience when vitroplant after 8 week into the greenhouse have passed to nurseries to reorganize their seasonal cycle and finally to be planted during the late winter or early spring, just before the sprouting. Thanks again.

Ricardo: Do you produce walnuts all months of the year? or is there a cutoff for planting out in the field in the spring? Do you prefer to keep producing microplants year round? The trick is for plants produced over winter, whether they go through dormancy properly, so that they flush in the spring. Plants acclimated in the spring seem to not flush. Perhaps the sequence is to grow roots, dormancy, then flush.