A change in sensitivity indicates that the concentration of hormone necessary to initiate a response is altered. Here, the term sensitivity refers to the response of a tissue or organ to a hormone. In contrast, fruit ripening involves changes in sensitivity of the organ over time. For example, during organ abscission adjacent cells respond differentially to hormonal signals. Hormone sensitivity can, in turn, be regulated both spatially and temporally. Regulation can also occur at the level of perception or signal transduction. Regulation can occur at the level of synthesis, transport, uptake, and turnover of the hormone. Plants have many ways in which to modulate hormonal responses. Hormones are the signals that integrate internal developmental and external environmental inputs and translate them into appropriate responses. And in many cases, they determine the point at which it will die. They modulate how fast and in what direction an organ grows.

Phytohormones are responsible for integrating many aspects of plant growth and development.

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