If you spray your solution onto the plant, you are not doing anything that rain doesn't do, hence buffering is unnecessary. It would be different if you were working with explanted tissue, single cells or isolated organelles. In that case one would use a buffer that mimics the environment inside a plant. This could be as simple as mannitol for osmotic pressure and 10 mM Hepes or Tris for pH.

Btw, autoclaving is performed for sterilisation, but if you dissolve a non-sterile compound in sterilised water, the solution will be no longer sterile. Thus, sterilisation should be done after all substances have been dissolved, if the solutes do not survive autoclaving, use another technique like sterile-filtration. Does the solution have to be sterile at all? Rain water isn't sterile either.

I think you need to carefully rethink your experimental protocol.

Hello Jyoti,

Engelbert Buxbaum is absolutely right. Nothing to add to his suggestions!

Best wishes, Peter