I think all plant parts like root, stem, leaves and also fruits are important for Halophytes study.

I suggest to work on xylem sap since it translocates all the metabolites etc

All parts are important. But you should also remember that whole organ analyses for ions and other components hide really big differences between tissues, cells, and even cellular compartmnets

i am also totally agree with both the comments. As per research first i have to try whole the plant part then after specific

But its difficult to prepare extract from whole plant ? Is there any some easy technique ?

Depends what you want to analyse. If you just want Na, K and Cl then a water extraction is fine. If you want other elements then you may need an acid digest of some description. And organic components all have their own extraction procedures. There is no one technique that will get you everything!

In my point of view whole the plant is necessary, and for extraction it's depend on which components you want, sent them to me and i give you the protocoles.

as per my knowledge, its depend on your study, which type of study u want to carry out with that particular extracts, for ex. if you want to study the antimicrobial activity then you need to extracts the different solvent extracts with increasing polarity, i.e., hexane, petroleum ether, ethyle acetate, chloroform, acetone, methanol, ethanol and aqueous. commonly extraction process is by hot extraction using Soxhlet, in case of cold extraction- just weigh known amount of the same powder, leaf, stem, root, seeds, or whole plant you can select, in conical flask, then keep it on shaker for 8-10 days constantly with daily observation then filter it and dry it to get the extracts and weigh it. then continue with different parameter using this extracts,

I think both root and leaf are important, if ionic movement is to be studied in respect of Na,K and Cl-. For preparation of leaf organics, one can use either EtOH or MeOH

In my view, to study halophytes, as others mentioned it depends on your objective.Any how you concentrate on leaves mainly because the photosynthates are produced in leaves. Due to salt ,the immediate effect is on leaves only.Usually actively growing leaves will be taken for analysis.Methods you can follow differently.

Dear Jagruti, I would start with leaves, taking samples in the morning, noon and evening. Each period, will give you different readings. As second step root sample again in the same order. Combining the two readings, you can draw conclusions.