There's a big difference between feelings like dogs and feelings like humans! And another big difference between feelings like dogs and feelings like sheep.
If specific species of plants start showing for example pain when they see other plants suffer, and affection for other plants and their human carers, some people would stop eating those plants. They would become characters in kids' stories. People would start keeping those plants as pets. That would be the real way those plants would stop being eaten - no-one will want to eat potatoes after Sally's potato wags its tail at them. Ultimately, lots of people do eat dogs, so we can't really expect everyone to stop eating these plants.
If it's all plants, then we'd be in real trouble. All our livestock eat primarily plants. We'd start investing much more heavily in algae, plankton, yeast etc. (it will become a righteous act to serve Vegemite!), and also fish farming. Some people would pay a small premium for non-sensitive foods. People would probably increase their vegetable consumption once there were enough advertising campaigns about how much corn is factory-farmed to produce one kilo of beef.
Where people still farmed plants, there would be efforts to grow them more humanely, with low pollutants, more careful machinery and more spacing between rows so that the plants are not needlessly crushed by machinery, plants only grown in appropriate climates, etc. People would pay more for these humanely grown plants, the same way people pay more for free range eggs.