Negative feedback is a reaction that causes a decrease in a particular function as a response to a certain stimulus, it tends to stabilize the system.
Once a plant begins to experience water stress and starts wilting, abscisic acid (ABA) would start to accumulate in the leaves and force the stomata to close. The closing of the stomata would reduce transpiration and prevent further water loss. ABA would then affect second messengers, such as calcium ions, and cause potassium channels to open, causing a decrease in potassium ions. The accompanying osmotic loss of water would reduce guard cells turgor and lead to the closing of stomatal pores. ABA could also serve as an early warning system.
This is similar to human's blood glucose regulation because the blood glucose metabolism uses insulin which is used to increase glucose levels. ABA's effect in plants is similar to glucagon's effect in humans. When there is an excess of glucose within the blood, glucagon would be triggered to perform glucogenesis in order to lower the levels of glucose.
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