Industrial zones are where your citizens work in the city. These provide lots of Pollution so make sure you have Parks in your city to lower the amount. These also lower Land Values all around them except for Power Plants, which they benefit from. Also, parks don't have land value so they remain unaffected by Industrial Plots.
Land Value goes from -4 to +4, see this page's categories for more.
Note that Industrial and Power Plants are NOT the same. Power Plants increase Industrial land values and Industrial thrives from it, but they are totally different.