One major thesis of materialism is that consciousness emerges from activity of the brain (or sometimes the central nervous system). Therefore, it would be evidence against materialism if plants and single-celled creatures exhibited consciousness since they have neither a brain or central nervous system.  Although we can not ask a plant if it is consciousness it turns out that plants do exhibit consciousness like behaviour.  For example, plants react to stimuli in much the same ways animals do and they are also able to process information [4] [5].  Furthermore, it has also been shown that single-cell mold can learn from and anticipate events and shows signs of intelligence  [6] [7] [8] . 

In fact, plants have all the same senses as humans, and then some. In addition to hearing, taste, for example, they can sense gravity, the presence of water, or even feel that an obstruction is in the way of its roots, before coming into contact with it. Plant roots will shift direction, he says, to avoid obstacles.  In addition, plants respond to anesthetics. "You can put a plant out with a human anesthetic. ... And not only that, plants produce their own compounds that are anesthetic to us." [11]  In addition plants seem to remember stresses and events.They do have the ability to respond to 15 to 20 environmental variables [11].

Below is a documentary (52 minutes) looking at some of the latest ideas and research on the sentience of plants.