you can add   PEG   (6000-8000) to you containing nutrient solution and  using  a semi-permeable membrane to separate roots 

As Maher Souguir says, one simple method to induce water stress in hydroponic culture is the use of PEG8000 (Polyethilenglycol 8000). Take a look to this paper: http://www.sciencedirect.com/science/article/pii/S0176161710004852

where PEG8000 is used to induce drought stress in eucalyptus plants.

I hope this will help you.

http://www.sciencedirect.com/science/article/pii/S0176161710004852

use polyethyleneglycol PEG

Dear all, thank you very much for your contribution.

With kind regards,

Just think of PEG 

PEG is ok but under hydroponic growth media perhaps sorbitol 100 mM is also a nice way to induce drought. In our lab we have performed some experiments with this compound and the results were consistent. Good luck!

PEG works but there are some limitations and drawbacks associated with using PEG.  Suggestions for using PEG and caveats are described here: http://www.plantstress.com/methods/peg.htm

The most important issue is distinguishing between water stress and the (unwanted) direct effects of PEG.  One approach, for which there are examples in the literature, is using dialysis membranes to disentangle effects of water stress from those of PEG.

you can use flat pots and a treatment basin with non penetratic solute, by. varying immersion duration you could mimick some water stress. all this is very unnatural and osmotic treatments are routine in germination tests, but there is room for experience

Thanks everybody for putting your suggestions in favor of PEG but in order to maintain the required  water potential for some period (2- 10 days)  how to apply PEG, either alone or in combination with Hoagland Solution or Preparing Hoagland in PEG solution.

Use PEG 6000 or 8000

with small plants you may try to use flat vessels and a treatment tank with known PEG osmotic pressure. A control tank would give the opportunity of going back to non stress condition . PEG 6000 cincentrazion should range near 15%, and  running water vessel between treatment s is suggested. Manipulation would be difficult  but some tomato seedling can support all this if the vessel hag got a frame for holding the shoot..

Hello,

I worked on this a PhD student 50 years ago!

At the risk of repetition and being egotistical you might like to read :

Lawlor DW (1969)  Plant Growth in Polyethylene Glycol Solutions in Relation to the Osmotic Potential of the Root Medium and the Leaf Water Balance  J. Exp. Bot. 20 (4): 895

Lawlor Dw (1970) ABSORPTION OF POLYETHYLENE GLYCOLS BY PLANTS AND THEIR EFFECTS ON PLANT GROWTH.  New Phytologist

DOI: 10.1111/j.1469-8137.1970.tb02446.x

Both are available on Research Gate

Regards

David Lawlor

Dear Kiflemariam,

I would like to endorse you a paper that might be of your interest. Hope it helps you!

http://www.sciencedirect.com/science/article/pii/S0176161710004852

I would really want to know if increasing the duration when the nutrient solution is pumped could serve as an alternative for drought induction other than the use of the PEG.