Based on our understanding of biology, a prerequisite for sentience is a central nervous system. Plants have really amazing abilities to pass chemical signals, but they lack any mechanics that would allow them to internalize the signals they receive. For example, I wouldn’t say that my doorbell is sentient just because it can warn me when someone is at my door. Importantly, animals are different from plants in their ability to internalize pain, fear, sadness, etc. This is why animal ethics and welfare are considered important discussions, and why it’s damaging to invoke plant sentience to distract from that discussion.