Righand your plant is showing signs of Magnesium deficiency and/or Potassium deficiency. Both of these cause the yellowing of the leaves between the veins. Potassium deficiency also causes they dry brittle edges on the leaves. I would water them with Epsom salts, 1 tablespoon to the gallon and a good dose of a high potassium fertilizer.
Look here for the symptoms
http://www.haifa-group.com/files/Gui...ato/Tomato.pdf