Every living being has to defend themselves in order to survive against predators. Animals defend themselves by attacking the predators or running away from them which isn’t possible in the case of plants as they are fixed to the ground. So, how do they defend themselves?
Plants get attacked constantly from microscopic fungi and bacteria to herbivores that devour plants for their diet. But plants don’t give up without a fight. They have internal and external defence.
The external forces start with the bark of trees that is full of lignin. Lignin is an organic polymer deposited in the cell walls of plants that make them woody and tough to chew and restricts pathogens from causing diseases. Leaves are covered in a layer of wax that repels insects and microbes. Some plants have thorns and prickles to defend themselves from animals and sharp hair-like structures on leaves to deal with smaller pests. Some plant species like pineapples, spinach, and kiwi have microscopic needle-shaped crystals that can cause tiny wounds inside the mouth of animals; these wounds become pores for toxins to enter.
Apart from chemical irritants and toxins released by plants that cause pain and inflammation when touched, plants can also guard themselves to stop predators from causing too much damage.
Plants don’t have a separate immune system rather every cell has the ability to detect and defend against predators and invaders. When plants detect a threat they signal their immune system to prevent pathogens from making their way inside, the wax thickens and cell walls get stronger. Guard cells seal the pores and if insects are devouring a part of the plant, those cells destroy themselves to stop the infection. Various toxins that are tailor-made for specific threats are released to fight off a predator.
When an area of a plant gets attacked they release hormones, airborne compounds, or electrical signals and alert other regions. Some species of plants receive these signals and help the one under attack by releasing insect repellent and prepare themselves to fight against microbes and insects by stocking compounds.