u need to solubulize ur tomato sample into SDS (10% solution) by heating it at 80 C for 1hr, then u need to determine the protein content of the solubulized protein (tomato sample) after centrifuging it....

then u can use the supernatant for runing a SDS page Gel.

Without tris buffer and beta mercaptoethanol ?

Just grind with NaCl up 0.9% (w/w) and mix for 2 h or so. Adjust pH to 4 and centrifugate around 3000 rpm. Supernatant contains protein enough for electrophoretic analysis.

You need to prepare your sample as follows::

27 ml of 5% (w/v) SDS solution were added to the sample (3 g). The mixture was then homogenised using a homogeniser at a speed of 13,500 rpm for 2 min. The homogenate was incubated at 85 ºC for 1 h to dissolve total protein. The samples were centrifuged at 3500 × g for 20 min to remove undissolved debris.

Now For solubulising your sample, you dont need to use tris-buffer and Beta mercaptoethanol.

Once u get the supernatant, then you need to determine the protein content of the supernatant by Buiret or Lowry method. After that you have to dissolve the known quantity of supernatant into the sample buffer. Then you can follow a general procedure for running a SDS PAGE gel.

Good Luck