Final answer:
In plant biology, reactive oxygen species (ROS) mediate the hypersensitive response, playing a critical role in plant defense by acting as antipathogenic and signaling compounds, while plant hormones like salicylic acid contribute to systemic acquired resistance.
Step-by-step explanation:
The mediators of hypersensitive response in plants are mainly attributed to the production of reactive oxygen species (ROS). These are highly reactive peroxides and oxygen-containing radicals that serve as signaling molecules to trigger defense mechanisms, including the programmed cell death known as hypersensitive response (HR). Plant hormones and other signaling molecules, such as salicylic acid, further amplify the defense response, but the initial trigger is provided by ROS. It has been well documented that ROS play a crucial role in plant defense strategies by acting as antipathogenic and signaling compounds, facilitating plant immunity.
Type II hypersensitivities, however, relate to the immune system in animals and are characterized by an immune response involving specific antibodies that target cells for destruction. In the context of plant biology and the HR that occurs in plants, ROS are considered the primary mediators of this localized cell death, which is critical for inhibiting pathogen spread and contributing to systemic acquired resistance (SAR).